1 2014 12 jaes

Journal of Applied Engineering Science 11(2013)4

I M P R E S S U M

J O U R N A L O F A P P L I E D E N G I N E E R I N G S C I E N C E (J A E S)

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Publisher

Institute for Research and Design in Commerce and Industry - IIPP; www.iipp.rsFor publisher: Prof. dr Branko VasićCopublisher

Faculty of Mechanical Engineering – Belgrade University; www.mas.bg.ac.rsFor copublisher: Prof. dr Milorad Milovančević

Faculty of Transport and Traffic Engineering – Belgrade University; www.sf.bg.ac.rsFor copublisher: Prof. dr Branimir Stanić

Editor in Chief

Prof. dr Jovan TodorovićFaculty of Mechanical Engineering, Belgrade;Assistant Editor

Dr Predrag Uskoković, IIPPEditorial Board

Prof. dr Gradimir Danon, Faculty of Forestry, Belgrade;

Doc. dr Dušan Milutinović, Institute for Transport and Traffic CIP, Belgrade;

Mr Đorđe Milosavljević, CPI - Process Engineering Center, Belgrade;

Prof. dr Miodrag Zec, Faculty of Philosophy, Belgrade;

Prof. dr Nenad Đajić,Mining and Geology Faculty, Belgrade;

Prof. dr Vlastimir Dedović, Faculty of Transport and Traffic Engeneering, Belgrade;

Prof. dr Mirko Vujošević,Faculty of organizational sciences, Belgrade;

Prof. dr Vladimir Popović,Faculty of Mechanical Engineering, Belgrade;

Prof. dr Vesna Spasojević Brkić,Faculty of Mechanical Engineering, Belgrade;Prof. dr Dragan Aleksendrić,Faculty of Mechanical Engineering, Belgrade.

ISSN 1451-4117 UDC 33

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Prof. dr Vukan Vučić,University of Pennsylvania, USA;Prof. dr Robert Bjeković, Hochschule Ravensburg-Weingarten, Germany;Prof. dr Jozef Aronov, Research Institute for Certification JSC, Russia;Prof. dr Jezdimir Knežević, MIRCE Akademy, England;Dr Nebojša Kovačević, Geotechnical consulting group, England;Adam Zielinski, Solaris Bus & Coach, Poland;Prof. dr Miloš Knežević, Faculty for Civil Engineering, Montenegro;MSc Siniša Vidović, Energy Testing & Balance Inc, USA;Dr Zdravko Milovanović,Faculty of Mechanical Engineering, Banja Luka.

Publishing Council

Prof. dr Milorad Milovančević,Faculty of Mechanical Engineering, Belgrade;

Milutin Ignjatović,Institute for Transport and Traffic CIP, Belgrade; Dragan Belić,Transport Company “Lasta”, Belgrade;Dr Deda Đelović, Port of Bar, Bar;Dr Drago Šerović, Adriatic Shipyard, Bijela;Cvijo Babić,Belgrade Waterworks and Sewerage, Belgrade;Nenad Jankov, Power Plant Kostolac B, Kostolac;Miroslav Vuković, Mercator Business System, Belgrade;Dušan Đurašević, Euro Sumar, Belgrade.

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Printed by: Sigrastar, BelgradeDesigned and prepress: IIPP

Institute for research and design in commerce & industry, Belgrade. All rights reserved. Journal of Applied Engineering Science 12(2014)1

C O N T E N T S

Vera Murgul

FEATURES OF ENERGY EFFICIENT UPGRADE OF HISTORIC BUILDINGS (ILLUS-TRATED WITH THE EXAMPLE OF SAINT-PETERSBURG

1 - 10

Dr Nevenka Pavličić,Dr Mladen Perazić, Dr Dragan Đurić-Jocić, Dr Miloš Knežević

ENGINEERING EDUCATION IN THE FIELD OF CIVIL ENGINEERING11 - 18

Viktor Pukhkal

EXPERIMENTAL ESTIMATE OF THE HEATING APPLIANCES HEAT FLOW PARAMETERS

19 - 22

Nenad Fric, Dr Dragan Buđevac, Dr Zlatko Marković, Jelena Dobrić, Dr Jovan Isaković

HUCK BOBTAIL FASTENING SYSTEM - NEW SOLUTION FOR HIGH-STRENGHT LOCKBOLTS

23 - 28

Dr Victor Vasilievich Elistartov, Dr Miloš Knežević, Roman Denisov, Michael Konishchev

PROBLEMS OF CONSTRUCTING WIND-DIESEL POWER PLANTS IN HARSH CLIMATIC CONDITIONS

29 - 36

Darya Nemova, Vera Murgul, Viktor Pukhkal, Alex Golik, Eugene Chizhov, Nikolay Vatin

RECONSTRUCTION OF ADMINISTRATIVE BUILDINGS OF THE 70’S: THE POSSIBILITY OF ENERGY MODERNIZATION

37- 44

Dr Luisa María Gil Martín, Dr Enrique Hernández Montes

OPTIMAL CROSS-SECTIONAL DESIGN FOR MINIMUM EMBODIED ENERGY 45 - 50

Dr Miroslav Premrov, Boštjan Ber, Dr Andrej Štrukelj

RACKING RESISTANCE OF PREFABRICATED TIMBER-GLASS WALL ELEMENTS51 - 56

Anka Starčev Ćurčin, Dr Đorđe Lađinović, Aleksandra Radujković, Andrija Rašeta

CAPACITY DESIGN OF RC MULTI-STOREY FRAME ACCORDING TO EN 1998-157 - 62

Marijana Lazarevska, Milivoje Milanović, Dr Miloš Knežević, Dr Meri Cvetkovska, Ana Trombeva Gavrilovska, Dr Todorka Samadzioska

AN ARTIFICIAL NEURAL NETWORK PREDICTION MODEL FOR FIRE RESISTANCE OF COMPOSITE COLUMNS

63 - 68

Dr Ivana Štimac Grandić

INFLUENCE OF SAMPLING INTERVAL ON DEFLECTION - INFLUENCE - LINE BASED DAMAGE DETECTION IN BEAMS

69 - 74

Dr Marko Pavlović, Dr Milan Spremić, Dr Zlatko Marković, Dr Dragan Buđevac, Dr Milan VeljkovićRECENT RESEARCH OF SHEAR CONNECTION IN PREFABRICATED

STEEL - CONCRETE COMPOSITE BEAMS75 - 80

Dr Cristina Campian, Alina Haupt-Karp, Maria Pop, Dr Nicolae Chira, Gabriel Urian, Dr Paul Pernes

BEHAVIOUR OF FULLY ENCASED STEEL-CONCRETE COMPOSITE COLUMNS SUBJECTED TO MONOTONIC AND CYCLIC LOADING

81 - 88


C O N T E N T S

Prof. dr Miloš Knežević

Sincerely yours,Prof. dr Miloš Knežević

Dean of the Civil Engineering Faculty in Podgorica President of the GNP 2014 organisation committee

XXI century will be the century of engineers.

Fifth time in Zabljak, traditionally held on conference Construction - Sci-

ence and Practice, with desire to share scientific and technical achieve-

ments - one that we materialized in expanse, as well as those who are

waiting for better times. Horizonte GNP, this time makes 271 work re-

viewed and selected for publication, signed by 511 authors from up to 20

countries around the world. As before, this time was organized a larger

number of round tables covering discussions about current issues. One

of them is education in construction because education of engineers is

about investment in the future, especially in XXI century which will be the

E D I T O R I A L

89 - 93Dr Marijana Serdar, Ana Baričević, Dr Dubravka Bjegović, Dr Stjepan Lakušić

POSSIBILITIES OF USE OF PRODUCTS FROM WASTE TYRE RECYCLING IN CONRETE INDUSTRY

95 - 99Maja Jevrić, Dr Branislav Popkonstantinović

BUILT ENVIRONMENT FRACTALITY AS A CRITERION OF SPACE MANAGEMENET

100 EVENTS REVIEW

101 - 102 ANNOUNCEMENT OF EVENTS

103 BOOK RECOMMENDATION

105 - 112 EDITORIAL AND ABSTRACTS IN SERBIAN LANGUAGE

century of engineers. Without achieved quality in education no one can provide appropriate answer

about time that is upon us, and that requires serious approaches to education. Therefore, conclusion

is necessity of continuing education throughout life that has its deep roots and good practise in engi-

neering at the most respected European technical universities. GNP, as well as each our business,

wouldn’t be as quality without participation of those who transfer knowledge and skills. Therefore,

with us in Zabljak were students and recently graduated engineers with their presentations and vi-

sions. Hopefully, in time that is upon us, we will combine our efforts and culture in construction and

we will build structures for next generations to be proud of. We thank the members of the Scientific

Committee and authors, especially the sponsors and friends who have supported us and helped us

in organization and maintaining Conference GNP 2014. Without their help, this could not be real-

Paper number: 12(2014)1, 268, 1 - 10

FEATURES OF ENERGY EFFICIENT UPGRADE OF HISTORIC BUILDINGS (ILLUSTRATED WITH THE

EXAMPLE OF SAINT-PETERSBURG)Vera Murgul*National Research St.Petersburg State Polytechnical University, Russia

doi:10.5937/jaes12-5609

* National Research St.Petersburg State Polytechnical University, Polytechnicheskaya st., 195251, St.Petersburg, Russia; [email protected]

1

Original Scientific Paper

In most European countries, including Russia, the requirements for building heat insulation are in-creasingly stringent. Historic buildings have become “energy inefficient” in terms of walling thermal upgrading aimed at reduced energy consumption. However, unlike the mass series of buildings, the historic ones are of cultural and architectural value. The energy efficient upgrade must not result in the lost of their historical authenticity. The article questions the applicability of existing standards for the thermal insulation of historic buildings, in particular, the “pros” and “cons” of walling thermal insu-lation. It discusses the need to preserve the exterior of the buildings that are monuments of history and culture as well as the historically-formed construction system. It puts forward the idea of improv-ing the quality of indoor climate in residential buildings instead of energy savings at all costs.Key words: Energy efficiency, Historic buildings, Reconstruction, Upgrading, Thermal insulation, Heat insulation

INTRODUCTION

Improved energy efficiency of historic buildings

is one of the most urgent problems of construc-

tion science nowadays. Lower energy consump-

tion and energy saving technologies make it pos-

sible to comply with the standards of sustainable

development of the society and provide comfort

to every household [03, 12]. Energy consump-

tion of the municipal sector accounts for about

40 % of the total amount. So, reduced energy

consumption is the main goal of energy-efficient

renovation of old buildings. Besides, energy ef-

ficient upgrading of old buildings will improve the

indoor climate, reduce the cost of electricity and

heat, decrease carbon dioxide emissions, in-

crease present value of the building and improve

its condition and durability [08, 14, 33]. The con-

clusion is made on the basis of calculations and

analysis that approach should be selective when

it comes to historic buildings.

LITERATURE REVIEW

The concept of «Sustainable Buildings» includes

several major interrelated notions: a comfortable

indoor climate, maximum use of renewable ener-

gy, energy efficiency of the elements of the build-

ing as a whole [23]. Methods to achieve climate

comfort in low energy buildings in the areas with

the cold climate were described in many works,

in particular in Y. A. Tabunshchikov, M. M. Bro-

dach, P. Sormunen, H. Ehhort, J. Reiss, R. Hell-

wig, M. Morelli, H. Tommerup, L. D. Boguslavs-

kiy, V. K. Savin, V. A. Yezerskiy, P. V. Monastyrev

[5, 16, 17, 26, 27, 29, 30].

V. Fayst, I. Gabrieel, H. Ladener, D. Haas-Arndt,

Burkhard S. Darup, Heinz P. Janssen, H. Rehku-

gler, T. Rombach, J. Reiß, H. Erhorn, M. Reiber

made the great contribution in buildings recon-

struction methods based on the energy-efficient

home [04, 06, 08, 09, 11, 21, 22].

St. Petersburg has a great number of unique his-

toric buildings. The research aims to raise ener-

gy efficiency of historic buildings which includes

taking traditional measures to reduce energy

consumption as well as reconciling the inter-

ests of cultural heritage protection with ongoing

activities aimed at improving energy efficiency.

Another aim of the research is to analyze the his-

torically-formed construction system in terms of

its energy and environmental qualities.

METHOD, CALCULATIONS, RESULTS

For St. Petersburg, the normalized value of

heat consumption in residential buildings lies in

the range of 55 kW\h to 118 kWh\m2 per 1 m2

(SNiP 23-02), compared to the target value of


Vera Murgul - Features of energy eficient upgrade of historic buildings (illustrated with the example of Saint-Petersburg)

2 , 268

heat consumption in Germany which is EnEV

2009 and lies in the range of 30 to 70 kWh per

year per 1m2 of living space. The location of

St.Petersburg more to the north should be taken

into consideration [08]. One of the fundamental

differences between the Russian standard for

thermal protection and the national standards in

most European countries is the consideration of

the construction region in Russia. There is a no-

tion of “degree-day heating season” as there are

several climatic zones in Russia.

Russian Standard SNIP 23-02 “Design of build-

ing heat insulation” sets the requirements for:

Reduced total thermal resistance of building

envelopes;

1)

Inner surface temperature of the enclosing

wall and prevention of condensation on the

inner surface of the enclosing wall;

Specific consumption of heat energy for

heating buildings.

The requirements for building heat insulation

protection are considered fulfilled if the require-

ments of positions 1 and 2 or positions 2 and 3

are satisfied at the same time.

The set of measures to raise energy savings in

buildings can be represented as a sum of en-

ergy conservation and energy generation based

on renewable energy. Of the whole complex of

measures energy efficiency provides the great-

est effect at the lowest cost [18].

2)

3)

Energy efficiency in buildings

The concept of “passive house”

Optimization of energy con-

sumption

En

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Table 1: Energy efficiency in buildings

The special challenge is to develop the set of en-

ergy-saving measures for historic buildings, tak-

ing into account the uniqueness of the historically-

formed construction system, as well as the need

for the protection of cultural heritage objects.

The apartment house, a typical pre-industrial

building of St. Petersburg, was chosen as an

object of the study. This is a three-four-storey

house built with the purpose of renting apart-

ments. Each apartment usually occupied the

whole floor.

Based on the analysis of archival drawings and

technical documentation a typical structural di-

agram of an apartment building was identified.

The author also carried out a visual inspection of

buildings and took control measurements of the

main geometrical parameters.

The results of the study showed that the historic

buildings of St. Petersburg are characterized by

changing with height wall thickness. Minimum

thickness of the outer wall on the top floor was

2.5 bricks or 0.72 m, and 4 bricks (1.15 m) on



3, 268

lower floors. The peculiar “eternal” skeleton of

the building is made of massive brick walls and

basement vaults, with the floor and roof struc-

ture implying the possibility of periodic bulkhead.

Even in the 19th century most of the buildings

went through the reconstruction with the super-

structure floor. The historic brick was solid and

had dimensions of 280 mm x 140 mm x 70 mm,

sand-lime mortar was used for laying bricks

(Figure 1) [10].

Figure 1: The exterior of the bricks manufactured:a) at the end of the 18th century, b) at the beginning of the 19th century, c) at the end of the 19th century

The quality assessment of the heat insulation of

the outer walls of historical buildings is conduct-

ed by thermal imaging method. Using the ther-

mography, the hidden defects in the brickwork

and the extreme humidity spots in the walls can

be detected. [23, 24]. The original design condi-

tions obtained for St. Petersburg on the basis of

standards SNIP 23-01, SNIP 23-02 and SP 23-

101 are shown in Table 2.

Table 2: Design conditions

City - Saint Petersburg Symbol Units Value

Design ambient air temperature text

ºС -26

Design interior temperature tint

ºС -1,8

Duration of the heating season zht

сут. 220

Design interior temperature tint

ºС 20

Operating conditions of walling Type B (high humidity)

Relative humidity inside the building φ % 55

Degree-day heating season Dd

°C day 4796

Coefficient taking into account the dependence of the enclosing structure position in relation to ambient air n = 1

Normalized temperature difference between the interior temperature and the temperature of enclosing structure inner surface

∆tn

ºС not more than 4

Heat transfer coefficient of the enclosing structure inner surface α

intW/m2 °C 8,7

Heat transfer coefficient of the enclosing structure outer surface α

extW/m2 °C 23

Dew point interior temperature for the cold season t

dºС 10,7

Normalized heat transfer resistance of enclosing structure R

reqm2 • C/W 3,0786

Required thermal resistance of enclosing structure according to hygiene requirements R= n (t

int - t

ext)/ α

int ∆t

n

R m2 • C/W 1,3218


uniformity factor r:

Ro • r Rreq,

Ro = 1/ αint

+ (R1 + R2 + ...+ Rn)+1/ αext

,

The requirement for design temperature differ-

ence ∆t0 between the interior temperature and

temperature of enclosing structure inner sur-

face:

∆t0 ≤ ∆t

n

∆t0=n (t

int – t

ext)/ R

o • α

int

The requirement for minimum temperature in all

areas of inner surface of exterior walls int, °С in

relation to dew point interior temperature td (with-

out condensate formation).

int td

int = tint

– [n(tint

– text

)]/(Ro• α

int)

The results of normalized parameters calcula-

tion for the historic buildings wall with 2.5 bricks

thickness are shown in Table 3.

4 , 268

Required values of reduced thermal resistance

of other structures of residential buildings in rela-

tion to climatic conditions in St. Petersburg:

roofs and ceilings above passages

4.60 (m2 • C/W);

attic ceilings, above unheated cellars and

basements - 4.06 (m2 • C/W);

ground floor - 4.50 (m2 • C/W);

windows, balcony doors, shop and stained

glass windows - 0.51 (m2 • C/W);

lamps with vertical glazing-0.37 (m2 • C/W);

Modern standards stipulate the following re-

quirements:

Requirement for design heat transfer resistance

Ro, (m2 • C/W) of enclosing structure, without

heat transfer performance uniformity factor, is

determined by the formula:

Ro R

req,

taking into account heat transfer performance

-

-

-

-

-

Table 2: The results of normalized parameters calculation for the wall thickness of 2.5 bricks

№ oflayer

Material δi, m λi, W / (m • °С) Ri, (m2* ºC)/W Normal value

1Interior plaster - lime-sand mortar

0,02 0,81 0,0247

2

Brickwork 2.5 with ordinary clay brick density 1800

kg/m3

0,72 0,81 0,8888

3Stuccowork -

sand-lime mortar0,03 0,81 0,0370

∑δi = 0,77 ∑ Ri = 0,9505

1/αв

0,1149

1/αн

0,0435

Thermal resistance of enclosing structure “on coats” Ro (m2*ºC)/ W 1,1089 3,0786

Temperature of the inner surface, int, ºС 15,23 10,7

Temperature drop t0

4,77 4≤

Table 4: The results of normalized parameters calculation

Thickness of the wall, in bricksNormal value

4 3,5 3 2,5

Thermal resistance of enclosing structure “on coats”, Ro (m2*ºC)/W

1,6399 1,4670 1,2818 1,1089 3,0786

Temperature of the inner surface, int, ºС 16,78 16,40 15,87 15,23 10,7

Temperature difference ∆t0

3,22 3,60 4,13 4,77 ≤ 4

The calculation results for other wall thicknesses

are shown in Table 4.

The heat transfer performance uniformity factor if

taken into account will increase the gap between

the required value of the design thermal resis-

tance of enclosing walls and the actual values

obtained as a result of this calculation, as the

calculated value of reduced thermal resistance

Ro

r “on the façade”, with the window openings,

is always less than the calculated heat transfer


Journal of Applied Engineering Science 12(2014)1, 268 5

resistance of the wall Ro “on coats” without win-

dow openings (heat transfer performance unifor-mity factor r < 1). The heat transfer performance uniformity factor r for apartment buildings brick walls should not be less than 0.74, with the wall thickness of 510 mm, 0.69 with wall thickness of 640 mm and 0.64 with the wall thickness of 780 mm, respectively. As for the other two indicators, our calculations showed that condensation is not formed even at a minimum thickness of the brickwork of all mentioned above. A slight devia-tion from normal temperature difference between the interior temperature and the temperature of the enclosing structure inner surface is not criti-cal for the comfortable indoor climate.

So, we can make a conclusion that even thick walls of historic buildings do not meet mod-ern standards. It should also be mentioned that the historically-formed construction system has passed two century test of building operation, and it would be unwise to abandon it completely.

It should be noted that walling thermal require-ments in Russia have been changed many times. A specific heating characteristic of brick apart-ment buildings of different years of construction, erected in accordance with the current standards of building heat insulation can be given as an ex-ample (Figure 2).

Figure 2:The relation between the specific characteristics of the building heating and the gross building volume: 1 - built before 1930; 2 - built in 1930 – 1958; 3 - built in 1958 - 1995.

qо=Q/[V

g(t

int-t

ext)], W/(m3 0C),

qо – the specific characteristic of the building

heating; W/(m3 0C) [07]; Q - heat flow of the

building heating system, W; Vg - gross building

volume, m3; tint - averaged over all quarters in-

terior temperature, 0C; text - design ambient air

temperature for the cold season, 0C [15].

As it follows from the data shown in Figure 2, the

buildings erected before 1930 have the lowest

thermal loads, with the requirements for building

heat insulation at that period being quite low.

Since 1st September, 1995 buildings have been

designed with increasingly high requirements for

building heat insulation. Thus, the required ther-

mal resistance for exterior walls was:

Till 1st September, 1995 - 0,843 (m2 • C/W);

From 1st September, 1995 to 1st January,

2000,671 (m2 • C/W);

From 1st January, 2000 - 2,945 (m2 • C/W);

From 1st October, 2003 - 3,079 (m2 • C/W)

To meet the building heat insulation require-

ments until 1995 it was enough to have 510 mm

thickness of brickwork (2 bricks). Now, in order

to achieve standard resistance heat of enclosing

walls, corresponding to the value of 3.079 m2•0C/

W it is necessary to have a uniform 1.69 m thick-

ness of brickwork (a ceramic void brick with 1300

kg/m3 density on cement-sand mortar is taken

for the calculation; thermal conductivity =0,58

W/(m•°C). The required thickness of brickwork

-

-

-

-



should be enhanced taking into account the heat transfer performance uniformity factor.Thus, we can conclude that according to current design building heat insulation standards in Rus-sian, brickwork can not be regarded as an en-closing structure.A graph showing the relation between the en-closing structure thermal resistance R

o and heat

flow q passing through the building envelope is determined by the formula:

q= (tint

- text

)/R0, W/ m2,

R0 - thermal resistance to uniform brickwork

structure (without heat-conducting inclusions), m2•°С / Watt (Figure. 3).

Figure 3: Graph of the relation between the enclosing structure thermal resistance Ro and heat flow q passing through the building envelope.

The relation has the hyperbolic shape. Typical thickness of the envelope walls (570-1150 mm) of historic buildings with matching values of the thermal resistance to the heat transfer (from 1.1 to 1.64) (m² ºC)/W (on the graph the area is highlighted with a blue rectangular) provides protection on the peak of the hyperbola. Further increase in the thickness of the brickwork would lead to a slight reduction of the heat flow. Such a conclusion favours the historically established thickness of the envelope walls.

It would be advisable to insulate only those con-structions whose thermal resistance is lower than 1.32 m²•ºC/W, which is a sanitation require-ment. On figure 4 the relevant area is highlighted with a red rectangular.Nevertheless, thermal insulation is essential. The priority is given to the external thermal in-sulation.However, the main disadvantage of such insula-tion is that it affects the historic appearance of a building.

Figure 4: Energy efficiency upgrade of the historic building in Nürnberg. The building before the upgrade and after. Ludwig-Feuerbach-Straße 75, 90489 Nürnberg, Germany

6


, 268


Even if the building is not on the statutory List of Buildings of Special Architectural or Historic Inter-est, this insulation leads to the loss of the visual historic environment [13, 32].

Figure 4 shows the older building before and after energy efficiency upgrading. Thermal insulation of the façade affected negatively the original historic appearance of the building [28].

It is unacceptable to lose the historic appearance of buildings because of regular changes in regu-lations for thermal protection of buildings.In St.Petersburg the activity to conserve buildings of Special Architectural or Historic Interest com-bines techniques which are applied to construc-tions, environment and city planning. The overall city appearance, squares and streets of the his-toric centre are nationally protected along with the other heritage objects [19].

The buildings listed as of Special Architectural or Historic Interest are exempted from the Russian standards for thermal wall insulation. However, the decision about every building should be ap-proved by governmental authorities. The same situation is in Finland and Norway [27]. Conser-vation of the traditional Russian wooden architec-tural monuments meets smoother requirements for thermal insulation. Nevertheless, there are a great number of traditionally constructed build-ings which are not on the Protection List, but they are the ones which creates the visual concept of the historic buildings.

In spite of the priority of external thermal insula-tion for historic buildings, it can be more effective to use internal thermal insulation. The main ob-stacle of the internal thermal insulation - moisture condensation - can be removed by forming a va-pour barrier [01, 7, 25].

Another obstacle of the internal thermal insulation is a possible contact of the effective insulator, with an inappropriate compliance with environmental standards, with the internal building environment. An excessive attention to the energy efficiency has clouded a more crucial problem - provision of healthy microclimate inside the building.

Most older buildings in St. Petersburg are pro-tected as objects of Special Architectural or His-toric Interest. Every building has its own particular components under protections. In most cases it is prohibited to alter decorative façades, but it is al-lowed to alter internal layouts in compliance with the Governmental Office which protects the cul-tural heritage objects [19].

However, if the decision about the thermal insu-lation is made, the internal façade can be insu-lated externally. Hereby the decorative façade shall be insulated from inside.

DISCUSSION

Weighing up all “pros” and “cons” for thermal in-sulation of historic buildings façades, it is neces-sary to draw attention to the loss of brickwork qualities as an envelope construction. The main quality of the brickwork is significant thermal in-ertia which allows to smooth temperature peaks inside the building.

Solar heat at the day time and slow heat emis-sion into the inside space of the building dur-ing evening and night prevented buildings from overheating in summer time.

The problem of summer protection from over-

heating is not as crucial for St. Petersburg as the problem of thermal insulation. Historic build-ings have massive walls, which means consid-erable thermal inertia. The window area is not large. This prevents the living space from over-heating and keeps it cool at the dark time and in summer. This results from accumulating proper-ties and considerable thermal inertia of the mas-sive stone walls. In winter houses equipped with furnaces are heated only once or twice a day. The massive walls perform like heat accumu-lators. Thermal inertia of stone walls minimize cold bridging from doors and windows by mak-ing them insignificant. Internal insulation would break this energy interaction.

The historically established construction system is worth more careful attention. The study of its unique properties encourages to work out a complex of energy saving activities specially for historic buildings. The main construction fabric - sand-lime brick - is notably durable and environ-mentally friendly. Vapour-permeable sand-lime solutions and plasters contributed to maintaining healthy microclimate in dwellings.

External thermal insulation causes an uncon-ditional energy loss because of impossibility to accumulate the solar energy by massive brick walls.

The usage of passive solar systems to increase energy efficiency is not greatly effective. A spe-cial placement of translucent and non-transpar-ent building elements allows to control sun radia-tion flows and heat flows in dwellings. However, thermal energy accumulation requires massive

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Journal of Applied Engineering Science 12(2014)1 , 2688

construction elements. Thus the external ther-mal insulation obstructs the environment influ-ence. In this case solar heating can never keep the thermal balance of the building [20].

Brick envelope is the most durable fabric. More-over, this multilayer structure does not need re-pair and is not subject to damages. The service life of thermal insulation is long, 15-25 years. The increase in the resistance to heat transfer will undoubtedly cut heating costs, but at the same time it will lead to the costs of insulation production, installation, maintenance and dis-posal. Therefore the economic profit from the thermal insulation installation is slight.

Besides, thermal shield properties of the insula-tion construction will mostly depend on the qual-ity of installation, lack of excessive moisture in the construction during its usage.The damp layer of insulation is affected by numerous tempera-ture shifts over 0ºC, which reduces its service life [31].

Buildings with insulated walls suffer the highest heat losses from the uncontrollable ventilation. In order to reduce the heat losses it is necessary to draught-proof buildings and install controllable heat recovery ventilation.

Draught-proofing is one of the main principles in the Passive House concept and energy effi-ciency design and construction. The purpose of draught-proofing is the elimination of uncontrol-lable thermal energy leaks [06, 30, 02].

The changes in Russian regulations about air permeability for windows have been switch-ing to draught-proofing since 70s, last century. Requirements of air permeability for windows changed in the following way:

1971 - 18 kg/ (m²•h);

1979 - 10 kg/ (m²•h);

1998 - 5 kg/ (m²•h).

The natural ventilation system of multi-storey buildings is still traditionally based on air infiltra-tion through cracks and gaps of windows. There-fore we can conclude that imposing tougher re-quirements of air permeability for windows has been the first step to draught-proofing, which has led to worsening microclimate with inappropriate air interchange [29].

In newly designed energy efficiency buildings draught-proofing is combined with the instal-lation of controllable heat recovery ventilation. In older buildings energy efficiency reconstruc-

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tion is usually started by occupants who replace their old windows, providing natural ventilation, with new draught-proofed ones. Hereby air in-terchange reduces, microclimate worsens and damp rises. In these conditions, if the tempera-ture of the internal surface of the outer walls is not high enough, moisture can condense on this internal surface.

It is essential to switch from energy saving at all cost to microclimate improvement. One cannot save energy by risking life and health. The prior-ity target of the contemporary construction is to form the appropriate climate in living spaces. Mi-croclimate parameters are of energy nature and include: inside temperature, temperature of in-ternal surface in envelope constructions, inside air quality (which also has energy content, as it is determined by ventilation air interchange) [29].

Microclimate improvement in living spaces, steady development of the society through the review of production fundamentals and energy consumption are different ways to the same goal. This goal is to provide healthy nation today and quality life for future generations.

Energy consumption of a building depends on both thermal and technological properties of en-velope constructions and performance of heating and ventilation systems. Therefore it is necessary to focus on the reduction of energy consumption in these systems. Depreciation of equipment in-comparably overtakes the service life of building constructions. This is the thing worth focusing. Relatively frequent changes of regulations for heat saving properties of envelope constructions reflect high growth rates of heating and climati-sation technologies. Engineering equipment of a building is an integral part which can be upgrad-ed without considerable financial expenses. The upgrade does not interfere with the constructive building structure and does not damage the vi-sual historic environment.

CONCLUSION

The outcome of the research allows to make the following conclusions:

1) Energy efficiency upgrade of buildings re-quires a complex approach. The building is tra-ditionally considered as a single energy system. The same systematic approach must be used to energy upgrade.

2) Insulation of envelope constructions, such as envelope walls, tend to be considered as one of


Journal of Applied Engineering Science 12(2014)1 9

the main activities to increase energy efficiency in existing buildings. However, if it comes to his-toric buildings that the insulation of walls can be avoided, it is better to avoid it. The fact is that the loss of visual historic environment is incompara-ble in its importance with slight saving of energy resources.

In order to achieve the given standards it is bet-ter to focus on optimization of engineering equip-ment and production of energy in the building enclosure on the basis of renewable sources (solar or geothermal). In this case it is neces-sary to make calculations not by the given resis-tance to heat transfer in the building envelope constructions, but by an index of thermal energy consumption for heating a building.

3) It is feasible to protect not only the visual ap-pearance of historic buildings, but historically es-tablished construction system.

4) It is necessary to assess the economic im-portance of planned activities aimed at insulat-ing the envelope constructions in historic build-ings, i.e. comparison of investments into energy saving and cost of saved energy. In addition, it makes sense to calculate the reduction of CO2 emissions resulted from the above-mentioned activities.

5) It is necessary to switch from energy saving at all cost to microclimate improvement. One can-not save energy by risking life and health.

SUMMARY

The dwelling sector consumes 40% energy and

undoubtedly has to cut this consumption. How-

ever, the potential loss of the historic authenticity

in St.Petersburg historic buildings resulting from

the energy efficiency upgrade is as important as

energy saving.

Therefore when it comes to historic buildings,

it is better to focus not on thermal insulation of

the envelope of walls, but on energy production

based on renewable sources.

It makes sense to protect not only the visual his-

toric environment , but historic construction sys-

tem, which is unique, environmentally optimal

and tested by century-long working experience.

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Review Paper

Paper number: 12(2014)1, 269, 11 - 18 doi:10.5937/jaes12-5633

* University of Podgorica, Faculty of Civil Engineering, Cetinjski put bb, 81000 Podgorica, Montenegro; [email protected]

ENGINEERING EDUCATION IN THE FIELD OF CIVIL ENGINEERING

Dr Nevenka Pavličić*Faculty of Civil Engeneering, University of Montenegro, Montenegro

Dr Mladen Perazić Montenegro Business School, Mediterranean University, Montenegro

Dr Dragana Đurić-JocićFaculty of Media and Communication, Singidunum University, Serbia

Dr Miloš KneževićFaculty of Civil Engeneering, University of Montenegro, Montenegro

INTRODUCTION

The processes of globalisation, economic and political integrations, growth and development of multinational companies inevitably require changes to the business operations manage-ment, development of new skills and knowledge as well as the necessity to embrace the lifelong learning concept. These processes offer cer-tain advantages such as the use of new tech-nologies and open competition which reflects on personal development. Nevertheless, there are certain constraints in terms of unfavourable de-mographic and age structure of population in the European countries and Montenegro therein. A burden of legacy is seen in the inherited nega-tive selection of human resources, transitional phenomena which requires the employees to be more adaptable, legal and institutional frame-work not adjusted to reflect new business prac-tice, improper ownership transformations and socio-political impacts on the development of economy.

Faced with the challenge of growing demand for employees with the occupation-specific compe-tencies on one side and with a limited capacity and resources available for improvement of the quality of education on the other side, the educa-tional systems in many countries have reached

a turning point. An increasing importance of knowledge and innovation for economic growth, a growing dependence on technology and an increased demand for both traditional and new skills indicate that the globalisation is not only a tool and/or instrument for production but also a requirement for a change to the education sys-tem. Researches indicate that basic skills should be enhanced to include information, communi-cation and language competencies. According to Kulic and Despotovic, the learning society be-comes a prevailing vision and ideal. It is a social evolution based on lifelong education and learn-ing [08]. Ovesni deems that the need for longlife education has lead to differentiation among the existing and creation of new institutions, which consequently resulted in diversification in the adult education system at global level. [04]

According to P.Gazivoda, education endeavours should also continue after the school-age period so to enable distribution of knowledge and specif-ic types of education which will be more demand-ed by individuals and societies. Whole life repre-sents a continuous learning process, according to S. Milic.[09] From the aspect of economy, im-portance of the learning is considered in modern economic literature, with acknowledgement of the importance of higher investment in human re-sources. Changes in specific sectors have an

Economic growth is of a crucial importance to the prosperity of a society and its members and such growth is based on a good quality and competent labour. Educated and skilled human resources are one of the key factors to influence the positioning of a national economy in the international com-munity. A properly regulated educational system and availability of education, as well as the “learning society” culture appear to be a generator of economic, cultural and general social progress.Key words: Education, Engineers, Civil engineering, Human resources, Employment Agency of Montenegro


-diate effect on the workforce demand and de-mand for specific type of knowledge. The chang-es in employment which involve higher employ-ment in knowledge sectors and growing use of information and communication technology ap-pear in line with development of the knowledge economy. Such changes are obvious in the de-veloping countries, and have resulted in struc-tural changes in the workforce demand, thus having long-term effects on the education and vocational training systems.

Construction sector has a strategic role in the development of Montenegro, yet a striking scar-city in human resources is observed in this very sector. This is proved by the fact that most of the work permits for expatriate staff have been issued for the job profiles within this sector, with the scarcity indentified at all levels of education. According to the data of the Employment Agen-cy of Montenegro, in recent years the highest scarcity has been recorded in the supply of the following job profiles: carpenter, brick mason, steel-bender, construction equipment operator, tile slabber, insulator, geodetic technician, civil works and building construction technician, geo-detic, architecture and civil engineer.

ECONOMIC FUNCTION OF EDUCATION IN EUROPE

More developed countries of EU advocate the idea of human potential being priority and key development resource, the quality of which primarily depends on adequate education and training. The quality of education and train-ing is expected to contribute to the growth of national economy, development of human re-sources, sustainable national development and general well-being of individuals. For this rea-son, countries with market economy promote education and human resource development as a strategic objective. These countries are committed to a systemic and at national level planned development of education and train-ing which highly benefits to economic growth, social progress and cultural development of general society as well as to the personal de-velopment of the members of society.

In the 21st century, impact of globalisation on the society, institutions and individuals has brought to changes in the educational strategies in the more developed countries in Europe. This mat-ter has been a subject of numerous studies and

researches which are based on different view-points - economic, political and cultural. Accord-ing to Prof D. M. Savicevic PhD, the globalisa-tion represents a new challenge to the education and learning and any neglecting or ignoring of the globalisation phenomena would not be fruit-ful to the concept of scientific thinking. [02]

What is typical for the research of the Euro-pean integration processes, in particular with a view to establishing and functioning of Eu-ropean Union, is the fact that more and more areas occur in which the EU member countries are ready to give jurisdiction to a supranational union and its institutions.[03] One of these ar-eas refers to the issue of education. Coopera-tion in the field of education in EU is governed by Article 149 and Article 150, Chapter XI of the Treaty on European Union. [10] According to the mentioned articles, Member States are responsible for the content of teaching and the organisation of education systems and their cultural and linguistic diversity.

In the Lisbon Strategy [07] adopted by the Eu-ropean Council in 2000, EU set itself a goal to become the most competitive and dynamic knowledge-based economy in the world capa-ble of sustainable economic growth with more and better jobs and greater social cohesion. The overall strategy is aimed at competitive-ness, stimulation of research and innovations in the EU economy. The Member States are called on to prepare certain documents such as the executive program for information so-ciety as a basic method for coordinated plan-ning and establishing of the information so-ciety. Marc Luyckx Ghisy [05] states that this decision is a business goal couched in the language of social inclusivity and sustainabil-ity. Its importance lay in its recognition that knowledge was becoming an important source of wealth. It was forward looking because in-stead of speaking of technologies, Europe’s political leaders spoke of a knowledge society. Also crucial for the future, they also linked com-petitiveness and sustainability. And in pushing for social inclusion they recognised the impor-tance of capitalising on the rising new logic of knowledge management. In a single statement, the Lisbon Summit meeting set the stage for a win-win scenario in the European Union for the first decade of the 21st century. [06]

Dr Nevenka Pavličić - Engineering education in the field

of civil engineering

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EDUCATION IN MONTENEGRO

A strategic goal of the educational system in Montenegro is to provide a quality education for all individuals by reflecting the demand of the la-bour market and to lay sound basis for further education and vocational training. Since its start in 2000, the implementation of the education re-form has brought many changes to the structure and organisation of the educational system.

The reform has been implemented in compli-ance with the EU trends and demand of the economic system which is constantly changing due to the development and daily progress in science and technology. For this reason, orien-tation to the lifelong learning has become ever more important. The lifelong learning is aimed at perfecting of the existing knowledge and skills and acquiring new knowledge so as to facilitate transition to new technologies and improve the position of an individual in the labour market.The educational system in Montenegro consists of: 21 public and 13 private preschool education institutions, 163 primary schools, 47 secondary schools (gymnasiums, professional schools and combined schools) and one private Gymnasium, 3 resource centres, 67 licensed providers of adult education.

Education is such area that needs constant im-provement taking into consideration the PISA test results of our students and employers’ per-formance assessments, position of our universi-ties in the world university rankings. Results of the research performed under the project “Evaluation of the Education Reform in Montenegro”, aimed at consideration and as-sessment of the level and quality of implemen-tation of the reform activities in primary schools and gymnasiums are the following:

Implementation of the reform agenda in the educational system in Montenegro proved to be necessary and resulted only in posi-tive changes,Reform of the educational system in Mon-tenegro significantly improved the quality of such system, A prevailing positive attitude towards the education reform is observed,Curriculums are effective, with all relevant learning objectives defined and knowledge standards clearly specified, The examinees highly ranked the quality of textbooks,

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Teachers to the large extent have compe-tencies which are directly related to the implementation of the specific aims of the reform,

Monitoring and improvement of the quality of education is at the satisfying level,

Material resources needed for the achieve-ment of the reform objectives are mostly satisfying,

Montenegro has taken a huge step forward in the area of legal framework and educa-tion polices, created a system setting for a quality inclusive education of children with disabilities.

High quality of the educational system and vo-cational education as a part thereof is important both for an individual and the society. Quality vocational education represents base for an up-grade of professional knowledge, skills and com-petencies which are necessary for life and work of an individual. In compliance with the General Law on Education and Law on Vocational Edu-cation, the vocational education in Montenegro is provided as a lower degree vocational educa-tion in the duration of two years, middle degree vocational education lasting three or four years and higher degree vocational education lasting up to two years as post-middle degree voca-tional education. The vocational education also includes the craftsman’s exam. The objective of the vocational education reform is to provide a more efficient response to the labour market de-mand. Development of qualifications is based on the performance results in all areas of work and at all levels of difficulty. It is important to ensure throughput in the educational system, to provide personal, social and professional development of any individual, and to enable comparability of the qualifications obtained in Montenegro with the qualifications obtained in other countries etc.

Considering that the investing in education of pro-fessional staff is a profitable investment and the safest path to successful business, and with an aim to reduce the discrepancy between the educa-tional system and real demand within economy, the Governing Board of the Chamber of Commerce of Montenegro at its session held on 14 March 2013, passed a Decision on establishing the Scholarship fund for secondary professional school students educated according to the curricula for scarce oc-cupations. The Fund is financed by those legal

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entities which state demand for the scarce qualifi-cations and by various donors. The award of schol-arships and other measures of professional orien-tation of students from the very beginning of the formal education process are intended to stimulate the interest of students and influence their orienta-tion to the scarce occupations. Enhancing cooperation between the entrepre-neurs and educational institutions represents an important aspect of the improving the educational system in Montenegro.

Higher involvement of the employers in the edu-cational system would enable better interaction and numerous advantages to either party. Tak-ing into consideration the identified tendency of the employers towards a “ready-made staff”, by provision of conditions for student practice the following interests would be satisfied: the in-terests of educational institutions ,which would enable acquiring practical skills rather than only theoretical knowledge; the interests of pupils and students who would be prepared for effi-cient inclusion in the work process and the inter-ests of the employers who would benefit from a good quality and trained staff and labour. This was one of the reasons to start with the Pro-gram of higher vocational education. The same type of program is also planned for the school students.

Comparative analyses of the European educa-tional systems performed in the recent years have acknowledged Montenegro as an active participant in reforms, consequently in the ac-cession process of Montenegro to the EU, Chapter 26 - Education and Culture was the first one to be temporarily closed.

CIVIL ENGINEERING EDUCATIONAL QUALIFICATIONS IN MONTENEGRO

Thirty-seven out of forty-nine secondary schools in Montenegro are professional or combined secondary schools. Within the formal education-al system in Montenegro, educational qualifica-tions for civil engineering jobs are provided indi-rectly in 23 professional secondary schools and directly in only 5 professional secondary schools in Podgorica, Berane, Plav, Nisic and Herceg Novi.

High education system in Montenegro comprises five faculties which provide educational for the vocation of civil engineer, these being the part of the University of Montenegro:

Faculty of Civil Engineering,

Faculty of Architecture,

Geodesy,

Faculty of Electrical Engineering, and

Faculty of Mechanical Engineering.

The structure of the educational process within the University in Podgorica is aligned with the modern trends in Europe. These faculties, re-corded for an evident growth in number of the enrolled students, offer base and post-graduate studies in different area based on the following models:

bachelor studies (3 years);

postgraduate studies (3+1)

master studies (3+1+1)

The formal educational system provides educa-tion for staff and labour for the labour market, however the problem lays in a regional scarcity and low mobility of these occupational profiles. The reason for regional scarcity and low supply of these occupational profiles in the labour market lays primarily in hard physical work, hard work-ing conditions, low earnings, away-from-home employment, temporary employment, insufficient occupational safety. According to the data of the Employment Agency of Montenegro, almost 2/3 of the scarce labour in the construction sector re-fers to the III and IV degree of vocational educa-tion. The employers in central and south region of Montenegro are in need for the labour with these qualifications due to the expansion of construc-tion works in these regions.

There are some attempts to solve the problem of scarce labour with the said educational profiles through the adult educational system, by means of retraining and additional qualifications. Non-for-mal education is provided by large number of the licensed instructors or those who act as NGOs and provide short non-licensed training courses. The Law on the Adult Education states that the adults can evidence the acquired knowledge, skills and competencies though sitting for exams before the Examination Centre, regardless of the manner of its acquisition. This is governed in more detail by the Law on National Vocational Qualifications.

National Education Council is responsible for the standards of knowledge that are established and verified by exams in case of evidencing the knowl-edge, skills and competencies, according to the educational curricula, on the basis of which or parts thereof, the publicly valid education is achieved.

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Berane Professional secondary school Civil engineering technician

Herceg Novi Combined secondary school “Ivan Goran Kovacic” Construction technician

Niksic The first professional secondary school Civil engineering technician

Plav Combined secondary school “Beco Basic” Architectural technician

Podgorica High school of civil engineering and geodesy “Inz. Marko Radevic” Architectural technician

Podgorica High school of civil engineering and geodesy “Inz. Marko Radevic” Interior designer

Podgorica High school of civil engineering and geodesy “Inz. Marko Radevic” Civil engineering technician

Podgorica High school of civil engineering and geodesy “Inz. Marko Radevic” Civil works technician

Podgorica High school of civil engineering and geodesy “Inz. Marko Radevic” Construction technician

Podgorica High school of civil engineering and geodesy “Inz. Marko Radevic” Hydro-construction technician

Podgorica High school of civil engineering and geodesy “Inz. Marko Radevic” Construction installer

Podgorica High school of civil engineering and geodesy “Inz. Marko Radevic” Tile slabber

Podgorica High school of civil engineering and geodesy “Inz. Marko Radevic” Dry construction fitter

The process of regulation of the adult education system is underway. The activities are focused on networking of formal, non-formal and informal edu-cation. So far, 24 educational curricula have been adopted for the work area - construction and ge-

Table 1. Secondary schools - Department of Construction and Spatial Planning” – by municipalities

and schools 2011/2012. Source: Ministry of Education

odesy. The educational curricula for vocational training for jobs in the fileds of construction and ge-odesy are assigned with the Level 2 of complexity and have been approved by the Adult Education Council.

CHALLENGES IN THE ENGINEER EDUCATION IN THE WORLD OF GLOBAL CHANGES

Near future will introduce a new paradigm which assumes the competitive advantage based not only on knowledge but innovation and creativ-ity as well. Any change to the education re-quires new tools for the highly qualified staff. Our students are due to accept basic concepts and principles of the market, marketing competi-tion and managerial roles. In addition to techni-cal skills and competencies, our civil engineers should also acquire management skills and abili-ties. The civil engineers should be prepared for team management along with good engineering knowledge. They are expected to operationalize their business ideas through plans.

The Faculty of Civil Engineering - University of Montenegro has acknowledge the above men-tioned and consequently established a study

program named “Civil Engineering and Manage-ment” taking on example of many similar schools across Europe and USA. It is intended for the staff familiar with the construction technology, legal framework, economic disciplines and bus-ies psychology, in other words the staff for new age. In general terms, the needs of an employer contribute to the adjustment of the creative inno-vative ideas to the actually measured potential results. Requirements set in our projects are always multidisciplinary - to build a hydro power plant? Yes, but the question is under which conditions. In essence, we assume high responsibility for creation of construction legacy of our lives and creation of future for the next generations. There are many pending issues that need to be solved in future. Our language is universal language of the world and our work will be appreciated by foreign audience visiting this region.



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The future times require a serious approach to the education of civil engineers that need to be considered in a long ran and based on multiple criteria. Unfortunately, at this point we have to mention that the financial situation of the Uni-versity of Montenegro is rather embarrassing when compared to other European universities and requires necessary and urgent measures to provide financial sources for both teaching and research activities. Otherwise there can be no substantial changes to the education as to re-flect the European standards.

Without the achieved level of quality in the field of education no proper response can be made to the time ahead us, such time imposing a need for serious approach to education. Deficiency in the energy will cause the kWh to become the measure of all values in the next few years. At our Faculty we have recognised this issue as well and we have started with implementation of the study program concerning energy efficiency in buildings under the scope of the postgraduate studies.

Most of the faculties of civil engineering in Eu-rope, within their educational curricula include the studies of environmental protection with a view to the technological protection measures, aimed at preservation of eco-systems, which in-evitably involves the sustainable construction.Curricula and syllabuses need to be aligned with the most recent scientific achievements and continuously reviewed to reflect the actual state of economy.

ACTIVITIES OF THE EMPLOYMENT AGENCY OF MONTENEGRO IN THE CIVIL ENGINEERING CAREERS

Montenegro is faced with a high level of structur-al unemployment.The data of the Employment Agency of Montenegro indicate an evident need for adequate labour in terms of both number and quality. A scarcity is recorded in craftsmen oc-cupation in construction, tourism and catering, agriculture and other sectors as well. The Gov-ernment of Montenegro endeavors to incentivise this area by setting a legal framework, primarily the Law on Crafts, establishment of the Chamber of Crafts, passing a rulebook on the Craftsman’s Exam , yet the results of the invested efforts are not as expected. Therefore, the attempts have been made to overcame the large structural mis-match between the labour supply and demand

by means of various short-term training and re-training courses organised by competent and li-censed adult education institutions.

Some additional education and training and re-training activties are organised in an attempt to mitigate this problem, however organisation of any comprehensive training programe requires by far larger financial resources, compliance with the regulation of the educational system and more active involvement of the Examination Center so as to provide that nationally recognised certifi-cates do guarantee the quality of the instructor training courses. It should be highlihted that the previous experiences in practical training of the unemployed persons show that well prepared training programs or training courses have been also well accepted by the unepmployed persons and employers.

With an aim to reduce the unemployment rate, the Employment Agency of Montenegro, acting through licensed companies, organises different types of training. The analyses performed by the Employment Agency of Montenegro suggest that all atendees of training courses for known employer manage to find the employment, while 70 % of trainees find their employment after

completion of the training course. For the pur-

pose of implementation of more complex training

programs, regular educational institutions are

also engaged.

The Employment Agency of Montenegro is highly

active in the area of the adult training, through dif-

ferent types of retraining and additional training

courses. The Law defined the Employment Agency

of Montenegro as a legal person, with rights, duties

and respinsabilities assigned to it in compliance with

the Constitution of Montenegro, the Law and Articles

of Association of the Employment Agency. The Em-

plyment Agency provides public serrvice with a pur-

pose of meeting demand in the field of emplyment

witthin the territory of Montenegro. The Employment

Agency operates under jurisdiction of the Ministry of

Labour and Social Welfare 5as well as the Republic

Pension and Disabilaty Insurance Fund. [11]

Activities of the Emplyment Agency of Montenegro

in this area are reflected through the following pro-

grammes:

Preparation for employment

Programmes of professional occupations

training

Programmes for known employer

Programme for acquiring special knowledge

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4.



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LABOUR MARKET IN MONTENEGRO

The labour market is characterised by continu-ously a continuously larger labour supply than labour demand, which is evidenced by a high un-employment rate. The market is also character-ised by an imbalance and mismatch in the struc-ture of supply and demand in terms of education, qualifications or regional distribution. The labour in the labour market needs constant improvement of knowledge, additional qualifications and re-training so as to achieve higher probability of find-ing the employment. The market also featured by seasonal employment with high employment rate of foreign nationals which recorded a sharp drop in 2013 due to the reduced quota of work permits. In 2013 total number of announced vacancies in Montenegro was 33.328, out of which 86,97%

were temporary employments. The largest num-

ber of vacancies was announced in the accom-

modation and food services sector 25,68%, trade

17,23% and construction 13,33%.

According to the data of the Employment Agen-

cy, register of the unemployed recorded 33.980

unemployed persons as on 13 November 2013,

which is 12,35% more than the year before.

The unemployment rate was 14,65%. The larg-

est number of unemployed persons is recorded

among those with VII (10.414), IV (9.371) and III

(7.037) degree of qualifications.

Construction sector is of major significance for

the economic growth of the country i particular

due to its multiplicative effect on other economic

activities. In the forthcoming period an increase

in contribution to the national GDP is expected,

especially in the period of the planned significant

financial investments in capital projects and the

pending highway construction project.

The construction sector engages large number

of employees in Montenegro. The table below

shows share of the employees working in the

construction sector compared to the total num-

ber of employees.

Table: Number of employees in the sector of construction and spatial planning

Number of employees in the sector of construction and spatial planning

Statistical Office of

Montenegro –Statistical

Yearbook of Montenegro

2011

Total employees Women% women to total employ-

ees

2008 2009 2010 2008 2009 2010 2008 2009 2010

Total 166.221 174.152 161.742 73.469 77.225 76.757 44.2 44.3 47.5

Construction 8831 9997 7903 1377 1367 1570 15.6 13.7 19.9

Source: Statistical Office of Montenegro – Statistical Yearbook of Montenegro 2011

CONCLUSION

In recent years development of human resourc-

es has become a subject of numerous studies,

analyses ad changes across Europe. This for

certain comes as consequence of the emerging

information techniques and technologies, chang-

es in labour market conditions, demand trends

in the employment sector, changes in economy,

social and political setting. The analysts have

put an emphasis on establishment of such edu-

cation and training system which will facilitate

the learners to acquire those skills, knowledge

and competencies that will enable them to adjust

to the new labour conditions, new types of work

and different working environment in a better

and more flexible way.

In many European countries the change pro-

cesses in education are underway or have al-

ready started. Given that formal education sys-

tem is the most complex and most diversified

segment of the lifelong education concept, the

changes needed are also quite complex and as-

sume different targets.

Modern tendencies of the countries with market

economy indicate that education and develop-

ment of human resources, with a view to new

technologies, are top ranked priorities of the

national strategies for socio-economic scien-

tific and technological progress. Modern eco-

nomic activities rely on highly qualified human

resources who possess knowledge and skills

needed to use new technologies effectively. De-

veloped societies are committed to the creation

of a “knowledge society”. The effects of creativ-

ity are now more achieved through knowledge.

As the effects of education do not reflect only

on individuals but on the society as a whole, the

knowledge is becoming a key development fac-

tor. Therefore, investing in education is another



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way to invest in human capital. It is important that not only information and science elites but total labour of one national economy acquire and apply new knowledge and information. [01]

Acknowledging the importance of the knowl-edge and development of human resources for economic growth and strengthening of the com-petitive position of Montenegro, the Montene-grin institutions, social partners and interested parties are investing joint efforts to achieve this goal. Their cooperation ad joint activities should be further enhanced as the research suggests there is still room for improvement. The knowl-edge based economy is not only a new para-digm, but rather a new technology which offers extraordinary results in terms of development of the country.

Which way forward to select and research? With a view to work and research activities, it would be useful to take the following steps:

Make an absolute and relative increase in public fund allocations for education and development of human resources as recom-mended at roundtables and by initiatives of the education community;

Reconsider total public investments as well as the investments in key segments of the education and training system and to tar-get investments to the specific areas which need improvement, to reallocate the existing investments to the lifelong development of human resources and to form a new concept in financing of the private educational institu-tions;

Develop sectors that will deal with develop-ment of human resources and promotion of importance of the lifelong education within the existing institutional framework and economy;

Affirm professional orientation and counsel-ling as one of strategic priorities in integra-tion of education and economy.

Calculate long-term demand of the construc-tion sector for education of persons for all job profiles in the overall demand planning.

Adjust educational curricula to match the de-mand of the construction sector

Make scholarship schemes for pupils and students as a reliable way of increasing the number of interested persons in the market of special occupations.

1.

2.

3.

4.

5.

6.

7.

Increase activities of the retraining and train-ing programmes

Economic growth is of a crucial importance to the prosperity of a society and its members and such growth is based on a good quality and com-petent labour. The educated and qualified hu-man resources are one among key factors to in-fluence positioning of a national economy in the international community. A properly regulated educational system and accessibility of educa-tion, as well as the “learning society” culture ap-pear to be a generator of economic, cultural and general social progress.

REFERENCES

8.



According to professor Zeljko Mrnjavac: Does Labour Disappear in the Knowledge Based Economy?

Dusan M. Savicevic, Comparative andro-gagy, Institute for Pedagogy and Andragogy, Faculty of Philosophy, University of Belgrade, Belgrade 2003, p.25

Gordana Ilic Gasmi, EU reforms – institutional aspects, IGP Prometej Belgrade 2004, pr. 14

Kristinka Ovesni, Education of Adult Educators, (European Experiences). Belgrade: Institute for Pedagogy and Andragogy, Faculty of Philoso-phy, University of Belgrade, Belgrade 2001, p.13

Marc Luyckx Ghisy PhD, mathematician, philosopher and doctor of theology, Member of World Business Academy and Dean of Cotrzgli Business Academy.

Marc Luyckx Ghisy, Win-Win Strategy for the European Union in the Knowledge Society, Quantum 21 net. 2007, p. 1

Presidency Conclusions, Lisbon European Council, 23 and 24 March 2000

Radivoje Kulic - Miomir Despotovic, Introduction to Andragogy, Zenica, Dom stampe 2005, p.29

Sasa Milic Strategy of the adult interactive learning, Actual problems of adult educaton, Scientific Symposiums, Book 82, Montenegrin Academy of Sciences and Arts 2007, p.90

The Treaty of Lisbon amending the Treaty on European Union and Treaty establishing the European Community 2007/C 306/01

www.zzzcg.org

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EXPERIMENTAL ESTIMATE OF THE HEAT FLOW PARAMETERS OF HEATING APPLIANCES

Viktor Pukhkal* Faculty of Engineering Ecology and Municipal Facilities, St. Petersburg State University of Architecture and Civil Engineering, St. Petersburg, Russia

The knowledge of radiant and convective heat flows distribution from heating appliances is re-

quired for a development of an efficient heating systemsmaintainingnecessaryconditions in rooms

at the lowest energy requirements.The study method is developed and provided. The heating ap-

pliances of water heating system (convection heater and radiator) are studied. The results of heat-

ing appliances heat flow measurements are given. Radiant and convective components of heating

appliances heat flow are determined.

doi:10.5937/jaes12-5631 Paper number: 12(2014)1, 270, 19 - 22

Key words: Heating, Heating appliance, Radiant heat flow, Convective heat flow

* St. Petersburg State University of Architecture and Civil Engineering, Faculty of Engineering Ecology and Municipal Facilities,

Vtoraja Krasnoarmejskaja ul. 4, St. Petersburg, 190005, Russia; [email protected]

INTRODUCTION

Optimization of the heating system is an impor-tant component of complex of measures, direct-ed at reducing energy consumption in new and renovated buildings [01, 02, 04, 06, 07, 10].

Heating appliances are divided into three groups by prevalent type of heat emission [03, 08]:

convective - emitting by convection no less than 75% of total heat flow;

convective-radiant - emitting by convection

between 50 and 75% of total heat flow;

radiant - emitting by radiation no less than

50% of total heat flow.

Heating appliances heat flow is determined by

an experiment without separation of radiation

and convection heat components [09, 11, 12].

Main factors determining heat flow values are

the type and the design of the appliance, and

-

-

-

the temperature lift - the difference between av-

erage heat carrier temperature and surrounding

air temperature for the appliance.

The estimation and analysis of heated rooms mi-

croclimate and the efficiency of heating energy

requirements would be possible only if convec-

tive and radiant heating appliances heat flows

are determined by an experiment.

PROBLEM STATEMENT

The experimental estimation of the heat flow and

its convective and radiant components is per-

formed for two types of heating appliances:

„Atoll“-type convection heater (PKN 310)

manufactured by „Isoterm OJSC“ (Russia)

(Figure 1);

„Profil-Kompakt“-type panel radiator (FKO

22-03-09) manufactured by „Kermi“ (Germa-

ny) (Figure 2).

-

-

Figure 1: Wall convection heater „Atoll Pro“



The basic model of „Atoll“ convection heater is designed wall-mouted and end-capped with side connections and is shown on the Figure 1. The frontal panel is convex-shaped.

Heating convector’s heating unit is made of cop-per pipes of 15 mm outer diameter and 0.4 mm thickness, and aluminum plates of 0.22 mm thick-ness profiled by horizontal and vertical swages. The plates are set on the pipes. The height of the plates is 100 mm. The plates fin step is 6 mm. There are 2 horizontal tubes in the plates for each 50 mm in height. The fin thermal contact with pipes is ensured by mandrelling of the pipes by 0.5 mm. The panel radiator consists of two rows of convective finning with 100 mm in depth and 300 mm in height located between the plates and welded to each panel.The U-shaped vertical finning is made of steel of 0.5 mm thickness and is spot welded to panels from backside directly onto walls of vertical heat carrier ducts. This design increases heat pickup from the panels mostly by convection.

The radiator is designed by „X2“ technology (Fig-ure 2). The technology is based on sequential heat carrier binding: the heat carrier from the sup-ply pipe first enters the front panel; the back panel functions as the reflective barrier. In that case heat losses are decreased because of the emission on cladding surface behind the radiator.

a) general view

b) heat carrier movement diagram [12]

Figure 2: „Profil-Kompakt“-type radiator (FKO 22) by „Kermi“

METHOD

To determine heating appliances heat flow we used an experimental apparatus measuring fol-lowing parameters:

Heat carrier’s temperature at heating ap-pliance entrance, exit and room air tem-perature - by platinum thermometers Pt500 which are part of „Multical 602“ heat meter;

Heat carrier’s flow-by an ultrasound flowme-ter from „Multical 602“ heat meater;

Heating appliance surface temperature-by surface thermometer Testo 905-T2 and the infrared imager (ThermaCAM E45 camera manufactured by „FLIR“ and ThermaCAM QuickView software package for report preparing).

Heating appliance surface temperature was measured by surface thermometer Testo 905-T2 only in static conditions as fixed points for infra-red imager measures control. It was necessary due to inertia in surface type instruments.

The cladding structure’s temperature was not controlled. Before each experiment (before turn-ing the heater on) the room’s thermal background image was shot.

Total heating appliance’s heat flow was deter-mined by heat meater data:

-

-

-

(1)

where:

G - mass heat carrier flow rate, kg/s;

c- heat carrier specific heat per unit mass, J/(kg•°С);

t1- heat carrier temperature at appliance

entrance, °С;

t2- heat carrier temperature at appliance exit, °С.

Radiant heat flow from heating appliance’s heat-ed surface to internal cladding surfaces [5].

(2)

where:

E - emissivity factor of mutually irradiating bod-ies; E= 0.9 for convection heater casing surface;

C - radiation coefficient of black body; W/(m2ºС4);

φ - irradiancy coefficient demonstrating which part of black body emitted energy reaches heating appli-ance’s cladding casing; for heating appliances φ=1;

20 , 270

Viktor Pukhkal - Experimental estimate of the heat flow

parameters of heating appliances


F - heating appliance heat-releasing surface area, m2;

tm.s

- heating appliance heat-releasing surface average temperature, ºС;

ts.r

- irradiatedsurfaceaveragetemperature, ºС; for under the window mount of heating appliance it is assumed as internal air temperature, ºС.

Convective heat flow from heating appliance:

(3)

where: - radiant heat flow from heating appliance’s front panel and side surfaces (radiant heat flow from top and bottom surfaces can be ignored due to its insignificance), W;

- convective heat flow, W.

ANALYSIS AND DISCUSSION OF THE RESULTS

The heating appliances are tested in conditions com-monly accepted for tests in Russia [11, 12].Radiant heating flow is calculated by mean values of each surface temperature: front, side and back. The ex-amples of thermal images are shown on Figure 3.

a) convection heater

b) radiator

Figure 3: Heat appliance front panel’s thermal im-agesunder testing

The convection heater testing has determined that radiant part of total heat flow is 4% and

convective part is 96%, respectively. Thus, con-

vective heat flow is a primal component and is

generated by heating air between ribbed heating

elements in the convective column formed by the

heating unit and the front panel and the wall. For

the radiator radiant part of total heat flow is 27%,

convective part is 73%. The convective heat flow

is a primal component in total heat flow and by

prevalent heat emission type the radiator is ap-

proaching convective appliances.

For the radiator’s back panel radiant part of to-

tal heat flow is 12%. The radiator efficiency can

be improved if the radiator’s back panel radiant

heat flow, which falls on the external wall, will be

decreased.

CONCLUSION

The method for experimental estimation of

radiant and convective heat appliances heat

flows is developed.

The experimental estimation of radiant and

convective heat flows is performed:

For „Atoll“-type (PKN 310) convection heater

manufactured by „Isoterm OJSC“ (Russia):

radiant part of total heat flow is 4% and con-

vective part is 96%;

For „Profil-Kompakt“-type (FKO 22-03-09)

panel radiator manufactured by „Kermi“

(Germany): radiant part of total heat flow is

27%, convective part is 73%.

REFERENCES

Cvetkovska, M., Andreev, A., Trpevski, S.,

Knezevic, (2013), Parametric analysis of

the energy demand in buildings with Pas-

sive House Standard, Conference, Portugal

SB13 Contribution of sustainable building to

meet EU 20-20-20, pp. 303-311

Cvetkovska, M., Knezevic, M., Rogac, M.,

(2012), Thermal insulation effects on energy

efficiency of building structures, Civil and En-

vironmental Engineering UGM, No. XXI/2,

Vol. 5, pp. 1209-1215.

Krupnov B.A., Krupnov D.B. (2010): Heating

appliances manufactured in Russia and CIS

countries, Moscow: ASV Publishing House

Lazarevska, M., Trombeva-Gavriloska, A.,

Knezevic, M., Samardzioska, T., Cvetkovs-

ka, M., (2012): Neural network prognos-

1.

2.

-

-

1)

2)

3)

4)

21, 270




tic model for RC beams strengthened with CFRP strips, Journal of Applied Engineering Science, № 1 (10), pp. 27-30.

Mikheev M.A., Mikheeva I.M. (2010): Basics of heat transfer, BASTET Publishing House, Russia

Murgul, V., (2012) Povysheniye energoeffek-tivnosti rekonstruiruyemykh zhilykh zdaniy is-toricheskoy zastroyki Sankt-Peterburga, Arkh-itekton: izvestiya vuzov, № 4 (40) pp. 54-62

Samardzioska, T., Trombeva-Gavriloska, A., Cvetanovski, P., Popovski, D., Partikov, M., (2012): Strengthening and overbuilding of car service «Automakedonija» in Skopje, Makedonija, Journal of Applied Engineering Science, № 1 (10), pp. 53-58.

5)

6)

7)

Skanavi A.N., Makhov L.M. (2008): Heating, Moscow: ASV Publishing House

Tiator I. (2006): Heating systems, Moscow: Tekhnosfera

Vatin, N., Nemova, D., Rymkevich, P., Gor-shkov, A., (2012), Vliyaniye urovnya teplovoy zashchity ograzhdayushchikh konstruktsiy na velichinu poter teplovoy energii v zdanii, Inzhen-erno-stroitelnyy zhurnal. № 8 (34). pp. 4-14.

Vitaterm LLC (2007): Reference manual for „Atoll“, „Atoll Pro“, and „Rodos“ convection heaters, Moscow

Vitaterm LLC (2013): Reference manual for „Ker-mi Therm X2“ steel panel radiators, Moscow

8)

9)

10)

11)

12)



22 , 270



HUCK BOBTAIL FASTENING SYSTEM – NEW SOLUTION FOR HIGH-STRENGTH LOCKBOLTS


Professional Paper

Nenad Fric*Faculty of Civil Engeneering, University of Belgrade, Serbia

Dr Dragan Buđevac Faculty of Civil Engeneering, University of Belgrade, Serbia

Dr Zlatko MarkovićFaculty of Civil Engeneering, University of Belgrade, Serbia

Jelena DobrićFaculty of Civil Engeneering, University of Belgrade, Serbia

Dr Jovan IsakovićTehnikum Taurunum-College of Applied Engineering Studies in Belgrade, Serbia

Alcoa Fastening Systems, introduces the Huck BobTail, representing the most advanced fastening

technology to date. Recognized as the next-generation lockbolt, the Huck BobTail delivers 5 times

the fatigue strength of conventional nuts and bolts, and is engineered to provide the highest level

of strength, reliability, and vibration-resistant performance. Engineered to meet the challenges of a

wide range of assembly applications, BobTail offers high performance and easy, quick installation.

Key words: Huck BobTail bolts, High strength bolts, Lock bolts

HISTORY OF HUCK BOBTAIL BOLTS DEVELOPMENT

Lou Huck invented the original Huck fastener in 1944, creating a whole new category of fasteners: Lockbolts (commonly referred to as Huckbolts). Initially designed as an aerospace solution to an aerospace problem, Lockbolt technology quickly spread to the transportation and heavy-equip-ment industries. Huck developed the C50L fas-tener for large-diameter applications (1/2” and above) shortly thereafter. The C50L (Grade 5) continues to be the preferred fastener for rail-roads and railcar manufacturers (Figure 1a).

The next leap in fastener design came during 1990’s with the HuckSpin fastener. HuckSpin combined the exceptional design characteristics of basic Lockbolts with sophisticated tooling to create a fast (very fast), efficient joining system while eliminating the pintail waste of previous Huckbolts (Figure 1b).

After more than ten years of rigorous road test-ing on trucks and trailers Alcoa designed U-Spin (Figure 1c). U-Spin assemblies are installed in pairs in just 10-15 seconds, using the classic Huck “spin on, swage, spin off” installation pro-cess.

Figure 1: a) C50L Fastener, b) HuckSpin Fastener, c) U-Spin, d) Huck BobTail Bolt

a) b) c) d)

* Faculty of Civil Engineering, Bulevar kralja Aleksandra 73/i, 11000 Belgrade, Serbia;

[email protected]


Equalized clamp force is exerted on each leg during installation, resulting in a level-loaded joint. Because their installation results in perma-nent clamp, U-Spin U-Bolts eliminate the need for re-torquing [01]. For over seven years it is standard in Volvo vehicle’s.

Bobtail Fastening System is designed to replace existing C50L pull-type fasteners, combines rug-ged light weight installation tools with a precisely engineered fastener to deliver superior value and benefits for the railroad industry (Figure 1d).

It goes above and beyond anything Alcoa Fas-tening Systems has ever produced for the heavy-duty fastener market and will continue to be the standard “for the long haul”. Of course, it is very important that Huck BobTail bolts find their place in construction industry. Aware of this fact, Alcoa engineers designed bolts with larger diameters than it is used in auto industry. With bolts diameter up to 25,4mm (1”) and appropriate lightweight tooling, considering very fast installa-tion and all other advantages (such as controlled preloading), there is no doubt that Huck BobTail fastening system will find its place on construc-tion industry market.

HUCK BOBTAIL BOLTS, COLLARS AND INSTALLATION TOOLS

Huck BobTail lockbolt is two-piece fastener that consist of bolt and collar (Figure 2). There are two types of bolt heads: round and flanged heads. There are few more types but they are available only on the special request. As about bolt diameters, there are small diameter imperial bolts with diameters: 3/16” (4,8mm), ¼” (6,4mm), 5/16” (7,9mm) and 3/8” (9,5mm), large diameter imperial bolts with diameters: ½” (12,7mm), 5/8” (15,9mm), ¾” (19,1mm), 7/8” (22,2mm) and 1” (25,4mm), large diameter metric bolts with di-ameters: 12mm, 14mm, 16mm and 20mm. De-pending of type of the bolt head and diameter of the bolt there are bolts made in strength classes 5.8, 8.8 and 10.9. Every of these bolts have their collar with appropriate dimensions and strength. All bolts are made of medium carbon steel or al-loy steel while collars are made of low carbon steel which is very important due to installation process. Bolts can be anticorrosion protected by zinc plate, Geomet coatings and oil while all collars are zinc plate coated [02].

Figure 2: Huck BobTail Bolts consisting of bolt and collar

The effective diameter of the bolt is reduced, al-lowing the bolt to stretch more when installed. The fastener has less pre-load loss caused by any seating of the joint. The bolt has been de-signed to have the same diameter all the way

from head to tail to allow easier alignment of joints. The reduced shank diameter allows a larger under head fillet radius to spread the pre-load of the fastener. It also improves the perfor-mance if installed under an angle. Large bearing

, 27124

Nenad Fric - Huck bobtail fastening system - new solution for

high-strength lockbolts


flanged head and large bearing flanged collar eliminates need for hardened washers and adds strength to the joint. Huck BobTail bolts have extended rolled thread which allows determi-nation of minimal grip by stroke length of the toll. The extension of the thread rolled area is possible because the BobTail thread is 6 to 10 times stronger than conventional thread. There is no thread inside the collar, only the “fit-up” tub which allows spun of the collar on the bolt thread before installation. Every collar have installation indicators on its flange. On the end of the pin is so called pintail. Diameter and length of pintail are designed to enable normal operation of the installation tool wich use pull grooves on pintail during installation.

INSTALLATION EQUIPEMENT

There are many different types of installation sys-tems for the BobTail, dependent of fastener di-

ameter, application type and application access. To install BobTail the basic tooling requirement is: powerig – to supply power to hydraulic tools (Figure 3a), installation tool – either pneumatic or hydraulic (Figure 3b) and nose assembly – to match with the fastener and tool [03].

A quick change of nose assembly from the in-stallation nose to the cutter nose (Figure 3c) enables removal of BobTail fasteners using the same tooling system. BobTail cutter nose as-semblies are available in same sizes as avail-able bolt diameters. In the beginning, systems for bolt uninstallation was having problems with heat distortion and damage, sparks and spatter. Now, cutter nose assembly works as a side cut-ting collar cutter (like nut splitter) which showed best results in practise. Usage of collar cutter will enable bolt removal and will not demage oder components.

Figure 3: Equipement for installation of Huck BobTail Bolts: a) Powering b) Installation tools,

c) Collar cutter nose asembly

a) b) c)

INSTALLATION PROCEDURE AND ITS ADVANTAGES

The BobTail System delivers a lightening-quick installation cycle time for greater productivity – as fast as two seconds (based on a typical installa-tion of a 5/8” Grade 8 fastener). This quick cycle is due, in part, to the short time required to ap-ply the tool to the pin and initiate the installation cycle. Once the operator engages the trigger, the swage and eject sequence is programmed to complete the cycle without any additional worker input. Installation process is shown on Figure 4.

The pin is inserted into the prepared hole, and the collar is spun onto the pin by „fit-up“ tab (Fig-ure 4 a). The next step in this procedure is apply-ing installation tool to annular pull grooves. When the tool is activated (red light on nose asembly is turned on) (Figure 6a), a puller in the nose assembly draws the pin into the tool, causing the swaging anvil to press on the collar against joint, drawing up any sheet gap (Figure 4b). At a predetermined force, the anvil begins to swage the collar into the pin’s lock grooves. Continued swaging elongates the collar and pin, developing precise clamp (Figure 4c). When swaging of the

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collar into the pin lock grooves is complete, the tool ejects the fastener and releases the puller to complete the sequence (Figure 4d) [02]. The installation indicator in the collar flange indicates

the BobTail collar has been fully swaged on. A quick visual inspection of highly visible indicators is all that is required to ensure complete installa-tion (Figure 5).

Figure 4: a) Bolt prepared for installation, b) Bolt pintail drawn into the tool,

c) Swaging of the collar, d) End of installation process

Figure 5: Installation indicators on collar flange before and after installation

In the initial stages of the installation process, the tool engages and pulls on the tail of the fas-tener. The joint is pulled together before the an-vil portion of the nose assembly is forced down the collar. This progressively locks (swages) it into the grooves of the harder pin. The pin and swaged collar combine to form the installed fastener. The squeezing action reduces the di-ameter of the collar, increasing its length (due to a constant volume of the collar). This in turn stretches the pin, generating a clamp force over the joint [03].

Compared to existing lockbolts and tension con-trolled bolts [04], the BobTail is designed with a pin-tail which does not require a pin-break. The benefits are reduced waste and weight as well

as a clean installation with low installation noise (pin-break at the large diameter bolts causes very loud noise). The lack of a pin-break also ensures a higher corrosion resistance (there is no uncoated area on the bolt) when compared to standard lockbolts with pin-break. There is no initiation points of corrosion and no secondary operations on the bolt after installation.

Absence of a pin-break improved worker hearing safety. Instances of foreign object damage and loose pintail injuries are eliminated. Because BobTail tooling features a smooth, shock-free in-stallation sequence, repetitive stress injuries are eliminated, there are no jolts to the operator’s arms and hands and overall safety is increased.

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Figure 6: Installation procedure of Huck BobTail bolts diameter 20 mm: a) red light indicates that

the tool is activated b) close-up wiev

Huck Bobtail lock bolts are not subjected to tor-sion during installation, so they can safely be taken to higher preload values than convention-al bolts. Their installation is under direct tension only. Conventional bolts are under a combination of tension and torsion during installation.

Full metal-to-metal contact between collar wall and bolt threads (Figure 7) eliminates the gap

usually found between threads in conventional nuts and bolts (in that case contact is made only on 30-35% of pin and nut thread area). Softer

collar material flows between lock-gooves of

hardened pin. The gap can lead to loosening in

vibration-intensive conditions common to wind

turbines, wind towers, bridges etc.

Figure 7: Contact between pin and collar/nut thread

CONCLUSION

In addition to these advantages and disadvan-

tages of Huck BobTail lock bolts, their price is

also very important parameter. As usually, price

depends of quantity. Based on the available infor-

mation a comparative analysis of the bolt prices

is made (Table 1). On the one side, there is high

strength bolt according to DIN 6914 standard,

bolt diameter 20 mm, grade 10.9 and on the oth-

er side Huck BobTail bolt [5], diameter 20 mm,

grade 8 (due to lack of information on the price for

grade 10). Both with grip length 30 – 40 mm and

both prices based on quantity of 100 pcs. Fol-

lowing a rigorous testing programme, the Huck

BobTail lockbolt fastener from Alcoa Fastening

Systems has earned the prestigious German

national technical approval, otherwise known as

allgemeine bauaufsichtliche Zulassungen (abZ),

in year 2013 [06]. An Allgemeine bauaufsichtli-

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che Zulassungen (national technical approval) is granted to products and types of construction for which there are either no generally acknowl-edged rules of technology or DIN (Deutsches Institut Fur Normang e.V.) standards. Declared by DIBt as “maintenance free”, the 12, 14, 16, 20 mm and 1 inch diameter BobTail is now ap-proved to be used in both static and dynamic civil engineering applications. The DIBt test con-firmed that a BobTail is maintenance-free during the lifetime of the joint it is fastening, which is

not the case when using traditional nut and bolt products. As a result, it can be integrated into a range of applications with complete confidence by civil engineering designers.

As about disadvantages, beside the lack of stan-dards and design criteria, it is very significant that Huck BobTail lockbolts cannot be retightened. Because of that, it is very important for design-ers to know the exact value of pretension force after installation of the bolt, but also during the life time of the bolt.

Type of the Bolt Bolt [EUR/1pc] Collar/Nut [EUR/1pcs] Washers [EUR/2pc] Total [EUR/set]

Huck BobTail M20, Grade 8 1,86 1,17 - 3,03

Peiner M20, Grade 10.9 3,21 1,02 0,68 4,91

Table 1: The comparative analysis of bolt prices

There are many experimental researches with Huck BobTail lockbolts carried out during the last few years in order to remove any uncertainties of their application and enable definition of design criteria. One of these researches started in Jan-uary 2012 on Faculty of Civil Engineering Uni-versity of Belgrade and still going on. Main target of this research is to determine installed value of pretension force in high strength bolts and also loses of pretension force during the time, due to type and thickness of zinc silicate anticorrosion protection in friction areas. This experimental re-search covers two type of bolts: Huck BobTail and high strength bolts according to DIN 6914 standard. All bolts are grade 10.9 and diameter 20 mm in three different lengths. Samples con-sisting of three steel plates and three bolts are exposed to two different loads: pretension forces in high strength bolts and 2*106 cycles of dy-

namic load. Measurement of loses of pretension

force is carried out for 8 months and provided

valuable information which analyses follows in

the next period.

REFERENCES

BobTail, Huck’s next generation lockbolt, Al-

coa Fastening Systems, 2010, http://www.al-

coa.com/fastening_systems/commercial/cat-

alog/pdf/huck/en/AF1032%20BOBTAIL.pdf

http://bayfastening.distone.com/Search/212.

all/48/name/cna/

http://www.afsglobal.net/afs-news.php?article=1

http://bayfastening.distone.com/Search/212.

all/48/name/cna/

http://www.afsglobal.net/afs-news.php?article=1

Nenad Fric, Boris Gligić, Jelena Dobrić, Zlat-ko Marković: “Wind towers – design of fric-tion connection for assembling sections of tubular steel towers”, Journal of applied en-gineering science, 10(2012)1, 221, 49 - 52, doi:10.5937/jaes10-1670

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Dr Victor Vasiliovich Elistratov - Problems of constructing wind-diesel power plants

in harsh climatic conditions

29

PROBLEMS OF CONSTRUCTING WIND-DIESEL POWER PLANTS IN HARSH

CLIMATIC CONDITIONS



Dr Victor Vasilievich Elistratov*Institute of Civil Engineering,Saint-Petersburg State Polytechnical University, Saint-Petersburg, Russia

Dr Miloš Knežević Faculty of Civil Engeneering, University of Podgorica, Podgorica, Montenegro

Roman DenisovInstitute of Civil Engineering,Saint-Petersburg State Polytechnical University, Saint-Petersburg, Russia

Michael KonishchevInstitute of Civil Engineering,Saint-Petersburg State Polytechnical University, Saint-Petersburg, Russia

The energy supply of buildings on the basis of renewable energy is a topical problem of the modern

construction science. Wind power is the most modern and perspective direction in renewable energy

both in Russia and Serbia. In the northern regions of Russia, the increase of reliability and efficiency

of power supply is suggested to be solved by constructing wind-diesel power plants and optimizing

the composition of equipment, parameters and modes of operation. In the article, the major problems

faced during the process designing of wind-diesel power plants in harsh climatic conditions are con-

sidered. The complexity is associated with building and using wind turbines. There are the problems

of transport logistics, of the construction on the permafrost, the installation and adaptation of equip-

ment to harsh climatic conditions. In the article, the major issues increasing the reliability of operation

are described. A number of considered issues are analyzed and solutions are proposed regarding

the design documentation to construction of WDPP in the Yamal-Nenets Autonomous District. The

recommendations for choosing the basic equipment are described. The parameters of WDPP with

high penetration are optimized using the software package HOMER 2.81.

Key words: Energy-efficient technologies in building, Wind-diesel power plant, Wind turbine, Building,

Harsh climatic conditions

INTRODUCTION

By the present moment, the development of re-newable energy sources (RES) in Russia has been supported by the legal framework on the one hand and by the economic incentives for the development of renewable energy on the whole-sale market in the centralized generation on the other hand. It has also been reflected in the RF Government Decree № 449 of 28.05.2013 «On the mechanism of promoting the usage of renew-able energy in the wholesale market of electrical energy and power».

At the same time 65 % of Russian territory is located in the autonomous areas of electricity supply including those in the northern regions. It means that the development of renewable en-ergy is an urgent task in the regions of decentral-

ized energy supply. In the northern regions of the country, the basis of power production is diesel power plants (more than 3 million kW). Most of them outlived their useful life long time ago. They have a very high fuel consumption level for elec-tricity production and consequently they have a high (up to 1 €/kWh) cost of energy production. As a rule, the development of renewable energy and economic efficiency in the autonomous ar-eas can be achieved by saving long-range fuel. As it is shown in Figure 1, the regions of decen-tralized energy supply are located on the terri-tory with high wind potential (with an average wind speed of 5 m/s and specific capacitance of more than 400 W/m2 [04]). The world experi-ence of the United States (Alaska), Canada, Fin-land, Norway and Sweden and other countries with similar climatic conditions proves that the

* Institute of Civil Engineering, 2nd Red Army Street 190005 Saint-Petersburg, Russia

[email protected]


most efficient way is to create wind-diesel power plants (WDPP) in the northern regions.

The implementation of WDPP provides the fol-lowing effects [07]:

enhancing of energy security of remote regions of Russia by increasing self-sufficiency in local fuel and energy resources;

15-20% reduction in energy loss due to the transmission and distribution of energy and therefore improvement of reliability and reduction of costs of energy for the consumer;

-

-

reducing the amount of long-range fuel;

greening regional power by reducing harmful emissions into the environment and reducing the volume of importation of diesel fuel barrels to the North.

The construction and the operation of wind-die-sel power systems in northern conditions require solving a number of problems: economic effi-ciency, providing quality power supply, delivering and installing equipment, constructing on perma-frost, etc. Let us briefly analyze these problems and their solutions.

-

-

Figure 1: Value of specific capacitance of wind flow in Russia at 100 m

THE PROBLEM OF INCREASING THE EFFECTIVENESS OF NORTHERN WDPP

The increase of the reliability and efficiency of power supply is suggested to be solved by in-creasing the penetration of expensive long-range fuel through optimizing the composition of equip-ment, parameters and modes of operation. The classification by the penetration class of WDPP is shown in Table 1 [03, 15].

The functional schemes of WDPP can be divided into two management options:

Diesel driven generators (DDG) work in the grid constantly and monitor the load. Wind

1)

turbines (WT) work in parallel with DDG and reduce the load on DDG to a minimum level (to save the fuel);

DDG may be switched off during periods of heavy production by wind turbines which can operate in the coating of the load without DDG.

The first option does not impose any specific requirements for the management system and does not require any use of special means of regulation. As it can be seen from the table, systems with low or medium penetration can be operated in this management option of WDPP.

2)

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Penetration class Operating Characteristics

Penetration, % Penetration, %

Peak Instantaneous Annual Average

LowDiesel(s) run full-time

< 50 < 20No supervisory control system

MediumDiesel(s) run full-time

50 – 100 20 – 50Requires relatively simple control system

HighDiesel(s) may be shut down during high wind

100 – 400 50 – 150Requires sophisticated control system

Table 1: Penetration class of WDPP

The system with medium penetration has a more complex control system that increases its cost. Additional costs are mainly compensated by the reduction of diesel consumption and, thus, by the cost of the fuel component.

As a rule, WDPP with a high penetration is the second option. When operating such WDPP, DDG are switched off during the periods when energy generated at WPP is enough to cover the load that provides maximum fuel economy. How-ever, this scheme requires additional equipment to control the frequency and voltage in the case of autonomous operation of WPP (subsidiary diesel generators, uninterruptible power supply

devices, energy storage systems) as well as a sophisticated control system [14]. The introduc-tion of schemes with high penetration provides greater fuel savings but requires increased costs. Therefore the adoption of a specific scheme is justified by comparing the technical and eco-nomic options.

The features of construction of WDPP in harsh climatic conditions are the following: the pattern of investment in WDPP in the northern regions is significantly different from the construction of wind farms in the temperate latitudes especially in terms of increasing transportation and con-struction workload (Figure 2).

Figure 2: The structure of the investment in the project of WDPP

The diagram shows that the construction, instal-lation and transport costs in the total investment are more than 35%. Therefore, it is extremely important to optimize and minimize these com-ponents.

THE PROBLEM OF TRANSPORT LOGISTICS OF WIND TURBINE AND ITS COMPONENTS

The lack of well-developed road infrastructure is the most important issue in the construction of wind turbines in harsh climatic conditions, which requires a more careful study of logistics. The

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Journal of Applied Engineering Science 12(2014)1 32 , 272

transportation of long blades of wind turbines re-quires a special transport, however, this transport has significant turning radius (Figure 3). Under these conditions, the delivery of marker equip-ment is a challenge. The presence of the curved sections (for example, in the mountains) with a large number of slopes and relatively small turn-ing radius requires the usage of special equip-ment cranes and trailers on which the equipment

is transported to the place of its installation [04]. In the Far North, the problems of transportation are associated with high dispersion of territorial settlements and poor transport links. The trans-port period for many northern regions is only 2-3 months and is carried out on temporary, un-equipped routes. One of possible solutions to this situation can be a helicopter delivery and the installation of wind turbines.

Figure 3: The transportation of blades

THE PROBLEM OF THE CONSTRUCTION OF THE WIND TURBINES FOUNDATION ON THE PERMAFROST

As a rule, the construction in Northern regions is associated with the construction on the perma-frost. The permafrost is regarded as soil exist-ing continuously in the frozen state for several years. Currently, permafrost in Russia is about a quarter of land.

Figure 4: The pile foundation with a high grillage

When building the foundation of any construc-tion project based on permafrost conditions, including wind turbines, have to be created so that the permafrost remains in a consistent state are necessary to create. As a rule, the founda-tions of these objects have a high grillage and a pile foundation allowing the creation of a venti-lated foundation (Figure 4). At the moment three types of piles are used in the construction of wind turbines such as drilled piles, drilling down (using lime-sand mortar) piles and in-situ piles (the frame filled with reinforced concrete in situ) [6]. The thermo-syphon cooling methods of pile foundation of wind turbines are also applied to preserve the integrity of permafrost so that in-service permafrost base is not thawed.

THE INSTALLATION PROBLEM OF WIND TURBINE IN HARSH CLIMATIC CONDITIONS

WPP is a unique construction which in contrast with chimneys has a massive system “rotor - na-celle” located at a considerable height above the ground which creates considerable external forc-es and requires unique cranes with a large arm for mounting elements of a tower, a wind wheel, a nacelle etc. In regions with poorly developed transport infrastructure where it is very difficult to deliver a crane jack-up, wind turbines are used which, however, have small nomenclature espe-cially for northern conditions [01, 80, 09] (Fig. 5). In remote places, the assembly by the usage of a helicopter is possible.




Figure 5: The installation of jack-up wind turbine

THE PROBLEM OF ADAPTING EQUIPMENT TO HARSH CLIMATIC CONDITIONS

In areas where the temperature drops below -30 ˚C rime is often formed, thus, we should fight

with glaciations of the equipment which can lead

to malfunction of the equipment and the disrup-

tion in power supply to consumers. In connection

with this problem, there are various deteriorating

situations depending on the type of equipment

and facilities to deal with them.

For blades; glaciations cause downtime. If

the wind turbine is in operation, the increase

in mass of the blade due to an uneven build-

up of snow can cause its destruction and can

endanger the safety of the object. The meth-

ods of deicing include:

heating systems blades;

paint blades black and/or a special hydropho-

bic polymeric coating which has improved

adhesion to sticking [16];

strengthening of special tapes in hazardous

to stick;

ultrasonic treatment methods of blades which

are now under development and experimen-

a)

-

-

-

-

tation.

According to the research, heating systems re-

quire a large power consumption for own needs

(10%) and increase the risk of fire.

Main power equipment is located in the na-

celle of wind turbines, so it is advisable to

ensure the safe operation of heating the

most critical components (gearbox, genera-

tor, control boxes, bearings, blades turning

control system, etc.).

For towers of wind turbines cold-resistant

low-alloy steel types are used in operation

at low temperatures [10]. Nickel of all the al-

loying elements lowers in the most degree

cold brittleness of steel. Nickel and iron are

completely soluble in each other; they have

similar crystal structure of lattices. The dis-

semination can get towers from low-carbon

steels as weldability improves with reduced

carbon content. Stairs leading to the gondola

must be necessarily inside the tower.

Stationary equipment (DDG, additional DDG,

batteries, control panels) is advisable to use

a block-container layout of equipment for the

adaptation of northern conditions. In a block-

container, the equipment is located in a well-

ventilated, heated, insulated and sealed place.

In the factory, settings are made «flat-to-flat».

In Russia such containers are produced by

several plants including plants «Zvezda», LLC

«SpetsElectroSistemy» [17]. One example of

a container is shown in Figure 6.

b)

c)

d)

Figure 6: Scheme of block-container «Sever»

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Changes of rate speed of the wind wheel and the power of wind turbine occur in the operation of wind turbine at variable-speed wind. Therefore sudden changes in the quality of issued electric-ity to consumer can occur which should be con-sidered by a control system and to be allowed to fluctuate within acceptable limits [12]. When designing WDPP, it is important to pay attention to the equipment belonging to the energy com-plex. Considering the fact that the northern re-gions are the regions of independent power sup-ply it is recommended to choose gearless wind turbines with synchronous generators with per-manent magnets (PMSG) and a full-scale power converter (Figure 7) [09]. The lack of gear signifi-cantly improves the reliability of the system to it allows wind wheel to work with variable speed. The work at low speeds ensures optimum power generation at low wind speeds. The application of full-scale power converter creates a galvanic isolation frequency in the circuit and increases the manageability of power quality at the end user by controlling the semiconductor elements.

Figure 7: Scheme of wind turbine with PMSG

A number of considered issues has been ana-lyzed and solutions are proposed in the design documentation construction WDPP in the Ya-mal-Nenets Autonomous District [02, 05]. The

object is located at 67˚ north latitude. Creation of

WDPP is suggested to be due to the extension

of two wind turbines to the existing DDG (two

DDG 256 kW) and the use of additional equip-

ment for special northern execution. There are

selected wind turbines Northwind 100 Arctic

(100 kW) from Northern Power Systems, USA.

These units feature high reliability thanks to

the maximum simplification of the structure and

reducing the number of moving parts by elimi-

nating the usage of gear using low-speed syn-

chronous generator with permanent magnets.

Distinctive features of the model NPS 100 Arctic

are able to function in a temperature range from

-40°C to +50°C and high humidity and the pres-

ence of special passive protection against icing

of blades in the form of a hydrophobic polymer

coating black. Nacelle of wind turbine is heated

to ensure the safety and comfort of personnel

during periods of repair or maintenance and ac-

cess to nacelle is possible by stairs located in-

side a tower. The tower of wind turbine consists

of three parts so it is the complexity of a design

flaw in the assembly for which one need to use a

crane with a large arm.

Calculations were performed using the software

package «HOMER 2.81» for optimization of the

equipment and modes of WDPP in v. Yar-Sale.

Operating window with example calculations is

shown in Figure 8. Software package allows to

simulate the composition of equipment, consid-

ering the wind speed, the oscillations of the load

curve, determining the fuel consumption for dif-

ferent schemes, as well as the cost of investment

for the options under consideration.

Figure 8: Operating window of HOMER

Calculations were performed for three options

schemes of the equipment:

With low penetration (DDG + 2 WT);

With medium penetration (DDG + 2 WT + add DDG);

1)

2)

With high penetration (DDG + 2 WT + add

DDG + batteries).

To select and justify the power of additional

equipment and energy storage systems authors

3)



Journal of Applied Engineering Science 12(2014)1 35, 272

propose efficiency functional F that generally represents the proportion of differential substitu-tion K

z power P (battery capacity C):

Additional DDG is selected in the power range from 6.5 to 105 kW and a block from 12 to 120

(1)

capacity batteries 200 A∙h. An additional diesel

generator capacity of 64 kW and a block of 24

batteries are selected from the Evaluation of the

function of the efficiency and feasibility study.

The scheme of the selected parameters and

equipment WDPP is shown in Figure 9.

Figure 9: Scheme of WDPP with high penetration

Scheme DDG

WDPP with level penetration



low medium high

Penetration, % 0 23 44 53

Fuel consumption, l/year 300,301240,814

(- 59,186)164,570

(- 135,731)136,881

(- 163,420)

Effect of introduction WDPP, K euro/year

0 60 90 108

Table 2. Techno-economic comparison of options schemes

Share of displace diesel fuel cost and estimated

effects from the introduction of each of the three

options are calculated in the software package

Homer. The main conclusions are summarized

in Table 2.




CONCLUSION

The urgency of building of WDPP in areas of independent power supply in harsh climatic conditions is substantiated, existing problems of construction WDPP are described and so-lutions to these problems are presented.

As the example of solutions to the problems listed above, the project of WDPP in Yar-Sale is considered.

As a result of the feasibility study, the com-position and parameters of the equipment of WDPP are matched to ensure high penetra-tion of diesel fuel.

As a result of the simulation the penetration of WDPP using automated and intelligent system power storage appeared to be 53 %. The fuel saving of WDPP was about 160,000 tons/year and the discounted payback period was 6.3 years.

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2)

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4)

REFERENCES

Cvetkovska M., Todorov, K., Lazarov, L. Axial restraint effects on fire resistance of statically indeterminate RC beams, Journal of Struc-tural Fire Engineering № 4(1), pp 47-58

Denisov R., Elistratov V. (2013): The use of WDPP with high penetration in distribution gen-eration, Abstract First Intenational Forum “Re-newable energy: towards raising energy and economic efficiencies”: Moscow, RAS, p 394

Drouilhet, Steve, Shirazi, Mari (2002) Recent Operating Experience with the Wales, Alas-ka, High Penetration Wind-Diesel System: Anchorage

Elistratov V. (2013) Renewable energy: Saint-Petersburg, Nauka

Elistratov V., Konischev M. (2013): Wind turbine operation in distributed and isolated generation, Abstract First Intenational Forum “Renewable energy: towards raising energy and economic efficiencies”: Moscow, RAS, pp 394-395

Elistratov V., Panfilov A. (2011) Design and operation of the renewable energy sources installations: Saint-Petersburg, Polytechnical University

Frye Jack A. (2006) Performance Objective Design of a Wind-Diesel Hybrid Energy System for Scott Base, Antarctica: Master’s Thesis

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Fric, N., Gligić B., Dobrić J., Marcović Z. (2012) Wind towers – design of friction con-nections for assembling sections of tubular steel towers, Journal of Applied Engineering Science, Vol. 10, No 1, pp 49 - 52

Iov F., Ciobotaru M., Blaabjerg F. (2007) Power Electronics Control of Wind Energy in Distributed Power Systems: Aalborg Univer-sity

IEC 61400 – 21, Wind turbine generator sys-tems. Part 21: Measurement and assess-ment of power quality characteristics of grid connected wind turbines

Kansara Bindu U., Parekh B.R. (2013) Dis-patch, Control Strategies and Emissions for Isolated Wind-Diesel Hybrid Power System, International Journal of Innovative Technol-ogy and Exploring Engineering, Vol.2, No 6, pp 152 - 156

Kanthwal A., Ganesh A. (2012): Hybrid Wind-Diesel Generation System, International Journal of Applied Engineering Research, Vol. 7, No 11, pp 1342-1347

Lazarevska, M., Trombeva-Gavriloska, A., Knezevic, M., Samardzioska, T., Cvetkovs-ka, M., (2012): Neural network prognos-tic model for RC beams strengthened with CFRP strips, Journal of Applied Engineering Science, № 1 (10), pp. 27-30.

Milovančević M., Anđelović B. (2010) Mod-ern techniques of wind turbine condition monitoring, Journal of Applied Engineering Science, №8, pp 33 – 38

Muhando, Billy, Keith, Katherine, Lundsage, Per (2012) Best Practices in Implementation of WIND-DIESEL SYSTEMS: AlaskaAlaska Center for Energy and Power

Zubarev V., Minin V., Stepanov I. (1989) Us-age of wind energy in North: state, efficiency conditions and prospects: Saint-Petersburg, Nauka

http://www.spelsy.ru/, retrieved on Decem-ber 6th, 2013

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36 , 272



RECONSTRUCTION OF ADMINISTRATIVE BUILDINGS OF THE 70’S: THE POSSIBILITY

OF ENERGY MODERNIZATIONDarya Nemova*Institute of Civil Engineering,Saint-Petersburg State Polytechnical University, Saint-Petersburg, Russia

Vera MurgulInstitute of Civil Engineering,Saint-Petersburg State Polytechnical University, Saint-Petersburg, Russia

Viktor PukhkalFaculty of Engineering Ecology and Municipal Facilities, St. Petersburg State University of Architecture and Civil Engineering, St. Petersburg, Russia

Alex GolikInstitute of Civil Engineering,Saint-Petersburg State Polytechnical University, Saint-Petersburg, Russia

Eugene Chizhov Institute of Civil Engineering,Saint-Petersburg State Polytechnical University, Saint-Petersburg, Russia

Nikolay VatinInstitute of Civil Engineering,Saint-Petersburg State Polytechnical University, Saint-Petersburg, Russia

The question of energy efficiency and energy saving has high degree of relevance. It was revealed that in

the view of considerable heat consumption the administrative buildings that had been constructed in Rus-

sia before 1996 require modernization. Built at their time and based on the actual at that moment stan-

dards of the thermal protection, nowadays these buildings became automatically unsatisfactory from this

viewpoint. At the same time their operating period is not finished, which means that those buildings do not

need a major overhaul. The paper presents an algorithm for upgrade of the thermo-technical parameters

of the framing as well as the parameters of overall energy consumption to the modern requirements with-

out complex reconstruction of the building or ceasing their normal functioning. The building selected for

examination is the “Uchebny corpus” of St-Petersburg Polytechnic University. This administrative building

is typical from both: construction and exploitation. That is why the conclusions made in this research can

be applicable to most of framed administrative buildings of the above period.

Key words: Energy efficiency, Energy saving, Insulation Coating, Heat conductivity, Payback period



INTRODUCTION

On power consumption of buildings the consid-erable part of developed thermal energy leaves. One of the main objectives of designers consists in improvement of quality of planning, architec-tural and construction concepts, depreciation of construction and power consumption of buildings and constructions, reduction of specific capital in-vestments on unit of the put into operation power.Over a significant period the requirements of tech-nical standards for thermal insulation in Russia were quite low [14]. For this reason currently the administrative buildings constructed before 1996 require a full-scale reconstruction of the building envelopes and modernization of the systems of

technical equipment (central-heating and ventila-tion systems) with the purpose of increasing the efficiency of energy consumption [23].

The necessity of the reconstruction is closely related to the approvement of the federal law № 261 “On Energy-saving, Energy Efficiency and Changes to the Legislation of the Russian Federation” dated November 23, 2009 [06]. The regulations imposed by this law are similar to the directive [01]. The problems of energy-sav-ing that are being solved by the European states are analogous to the problem considered in this article [03].

After 2000 with the changes in the Building Code II-3-79 (“Thermal engineering”) [19] and with the

* Institute of Civil Engineering, 2nd Red Army Street 190005 Saint-Petersburg, Russia

[email protected]


approvement of its updated version dated 2012 the requirements for the thermal resistance of building envelopes have increased by factor 2.5 [07]. Therefore, all the buildings that were con-structed before the legislative changes are obso-lete [08]. At the same time their operating period is not finished, which means that those buildings do not need a major overhaul [16].

In this paper outlined the possible ways of re-ducing the energy consumption of “Gidrokorpus 2” of Saint Petersburg State Polytechnical Uni-versity (Politekhnicheskaya Street, 29, Saint Pe-tersburg).

A number of research works is dedicated to de-crease of thermal losses in existing buildings re-construction. The actions directed on reduction of losses of heat and increase of level of ther mal protection of external protecting designs demand an integrated approach. The replacement of tech-nical equipment and the renovation of the building envelope are considered as the major measures to increase energy-saving [04, 09, 13, 18].One of the key problems that hamper the devel-opment of energy-efficient technologies is the ab-sence of the universal methodological approach to complex evaluation of economic efficiency of energy-saving technologies [02]. In many cases this is a reason for misleading conclusions that might cause mistakes in making financial deci-sions.

THE GOAL AND OBJECTIVES OF THE RESEARCH

The goal of the research is to elaborate a system of measures that allow to improve the thermo-technical characteristics of the building envelope and energy consumption of the building in the way that they comply with the modern standards and make it possible to avoid a major overhaul and an undesirable interruption in functioning of the building.

Considering the fact that there is a significant number of administrative buildings constructed in accordance with the obsolete frame models (during the indicated period), and in the view of the growing need for their reconstruction, it is clear that the development of a system of mea-sures is an important and scientifically relevant objective [14].

To define the basic measures it is necessary to consider the exact technical state of the building and its current energy consumption [15].

The thermal resistance of all framing construc-tions can be obtained basing on the thermo-tech-nical theoretical calculations. However, taking into account the long period of the preliminary ex-ploitation of these buildings it is highly desirable to perform a number of measurements. Hence, the below steps follow from the goal specified:

performing of the complex examination of the typical building,

based on that examination propose a list of transformations to avoid the complete overhaul,

find the optimal thermal isolation of the outer walls of the above type of buildings [18].

-

-

-

LITERATURE REVIEW

Significant contribution to the solution of theoret-ical and practical issues of energy efficiency and walling made the following scientists: Gorshkov A., Gagarin V.G., Trutneva M.S., Samarin O.D., Butovsky I.N., M.N. Efymenko.,Tabunschikov Y. A, Bohuslav L.D V.K. Savin, Yezerskiy V.A., Monastyrev P.V., Klychnikov R.Y. and many oth-ers [02, 05, 13, 17, 18, 19].

Measures aimed at reducing of heat loss and increasing heat protection of external walling al-ways demanded economic justification. Payback period of such events investigated Boguslavskiy L.D., Gagarin VG Samarin OD etc.

Boguslavskiy L.D. proposed a model that allows assessment of “economic utility”, “optimal” wall-ing thermal resistance [02].

Savin V.K. created thermogram of energy con-sumption dependence on the creation of the construction, operation costs, and its total costs presented in dimensionless form, the level of fencing thermal protection. By this procedure, you can select the most energy-efficient materi-als, constructions and building in general [19].Yezerskiy V.A., Monastyrev P.V., Klychnikov R.Y. in their works determined maximum lifetime of the building in which its Thermo will be break-even [24].

Samarin O.D., using techniques developed by specialists, members of the NP “ABOK”, consid-ered the effectiveness of investments in energy saving measures. In his works, he determined the influence of climate change on payback of additional warming Non transparent walling [17].The most consistent and reasonable approach was developed by Gagarin V.G. He proposed an

38 , 273

Darya Nemova- Reconstruction of administrative buildings of the 70’s:

The possibilty of energy modernization


improved mathematical model of payback condi-tions to increase the level of thermal protection that takes into account more and discounting saving operating costs. In his works, VG Gagarin compared the significance of interest rates, as well as heating degree-days period and the price of thermal energy in the cities of Russia and the EU and CIS countries [05].

METHOD

The primary research method was the technical examination of the building and of the systems of central heating and ventilation (with the evalu-ation of their condition). Based on the results of the above-mentioned examination, the elabora tion of the measures to improve energy efficien-cy was conducted [10].The building selected for examination is the “Uchebny corpus” of St-Petersburg Polytechnic University. This administrative building is typical from both: construction and exploitation. That is why the conclusions made in this research can be applicable to most of framed administrative buildings of the above period. Having no restric-tions on changing the initial appearance of the administrative buildings of that period gives a va-riety of opportunities for technical solutions from both: construction and design.

The results of building survey:

overall height of the building - 24,8 m;

heated area - 11180.79 m2;

heated volume - 43,605.08 m3;

total area of the exterior walls - 14,155.57 m2.

The survey of enclosing parts of building (Figure 1) [11]:

-

-

-

-

Figure 1: Appearance of the building

Examination of the ventilation system of the building

The complex examination of the system of me-chanical ventilation of the building was carried out (Figure 2).

total height of the building 24,8 m

heated area 11180 m2

building volume 43605 m3

total area of exterior walls 14155 m2

The exterior walls of the building have the follow-ing structure:

interior gypsum plaster 5 mm

brickwork of solid clay bricks on cement-sand grout 510 - 640 mm

cement-sand grout 20 mm

stoneware tile 10 mm

Filling of the window opening - double glazing (with wooden or metal separate window case-ment). Glazing factor – 0,29.

Prefabricated concrete roof with cool attic.

-

-

-

-

-

-

-

-

Figure 2: The survey results ventilation systems.

a) the basis for the placement of the air-ejector roof ventilator; b) destroyed ventilation airways on the roof of

the building; c) blowing ventilation systems in the “construction” performance)

39, 273




The examination revealed the following:

the technical equipment of the ventilation system are situated on the roof of the build-ing; the air-ejector ventilators are partly dismantled; the air-ejector airways are de-stroyed; systems do not operate;

the technical equipment of the draw-in venti-lation is placed in the inflow chamber, which is situated in basement; the mechanisms consist of separate elements and do not op-erate; the air-heaters are assembled with the violations of technical standards; systems and mechanisms are based on direct-flow principal; the systems of automatic regula-tion of heat consumption are not installed.

Thus it is obvious that the systems of mechani-cal ventilation are technically obsolete and must be replaced.

Examination of the central heating system of the building

The system of central heating has the following characteristics:

-

-

one-pipe dead-end system;

the system of automatic regulation of central heating equipment is default;

the system of automatic thermal regulation is missing.

The heating system, draw-in and exhaust sys-tems of ventilation of the building are obsolete and need to be replaced according to the mod-ern standards of energy consumption [17].

Resumes after shoot by thermal imagery device

Thermal imaging is characterized by high self-descriptiveness. The analysis of thermograms revealed the building sections with the highest heat losses. The spent shooting by thermal im-agery device has revealed defects of windows, doors and external envelops. To standard re-quirements there correspond only windows in plastic double-glazed windows. Consequently, it is clear that there is a need for the replacement of filling of the window opening and for winteriz-ing the outer walls of the building (Figure 3).

1.

2.

3.

Figure 3: Thermogram obtained by thermal imaging inspection of exterior walls and skylights.

RESULTS AND DISCUSSION

Required heat transmission resistance exterior structure for public educational institutions:

for the exterior walls -

for coverings –

for windows -

Calculated (design) value of heat transmission resistance of external envelop :

external wall - Rw = 0,656 (m2•ºС)/W < 2,433 (m2•ºС)/W;

coverage - Rc = 0,88 (m2•ºС)/W < 3,244 (m2•ºС)/W.

-

-

-

-

-

Windows for double glazing with separate metal casements:R

F = 0,34 (m2•ºС)/W< 0,51 (m2•ºС)/W.

Windowsfor double glazing with separate wood-en casements: R

F = 0,42 (m2•ºС)/W> 0,406

(m2•ºС)/W [20].

Filling of window openings should be replaced in order to reach the required value of reduced total thermal resistance [19].




The measures for the reduction of the heat losses of the building

In order to reduce heat losses through the outer walls and central heating system three variants

of winterizing are considered (Table 1):

a Rainscreen cladding;

a facade covered with a thin layer of plaster;

a facade covered with a thick layer of plaster.

1)

2)

3)

Variant of construction Scheme Structure

Rainscreencladding

insulated walls;brackets;vertical guides;frontal expansion anchor stud;insulation;ventilated air gap (40-60 mm);cladding panel

1.2.3.4.

5.6.7.

Facade covered with a thin layer of plaster

special adhesive mixture;insulating panels of rock wool;frontal expansion anchor stud;reinforcing filler;exterior glass cloth grid;water-dispersion primer;decorative mineral plaster;frontal silicone paint;ground profile;mating element;ground anchor;roughness compensator

1.2.3.

4.5.6.7.8.9.10.11.12.

Façade covered with a thick layer of plaster

fixing system consists of three parts: anchoring part, movable hook and three clamping plate;insulating panels of rock wool;plaster mesh;soil and leveling mortar;lime-cement facade plaster;cladding structure

1.

2.3.4.5.6.

Table 1: Variant of the exterior walls construction

The thickness of an insulating layer and estima-tions of the payback period of the reconstruction were calculated for the thermal resistance of ex-ternal walls that amounts to 2,433 (m2∙ºC)/W:

Rinsulation

=1,777 (m2∙C)/W;

dinsulation

≈125 mm. [04].

The preliminary analysis of the technical and

economic characteristics of the measures to

winterize the building envelope demonstrated

that the payback period can be considered as

the basic index [12].

Payback period can be calculated as follows:

year

where - , - cost of expenses for work on

warming of 1 m2 of the exterior wall, rub; [22]

- the difference between the heat losses cost

through 1 m2 of the exterior wall 1 m2 to events

on wall insulation and after warming ,rub/

year;

(1)

rub/year, (2)

- difference thermal energy loss per heating

period, Gcal/year;

- cost of thermal energy for consumers

(heat tariff). For Saint Petersburg in 2013

=1702,45 rub/Gcal including VAT; [21]

24

1000 1163

dU DQ

∆ ⋅ ⋅∆ =

⋅ (3)

hE Q C∆ = ∆ ⋅

Gcal/year

, 273




- difference coefficients of heat transmission, W/(m2•°C);

U∆

1 2U U U∆ = − , W/(m2•°C (4)

1/U R= (5) , W/(m2•°C

Dd- degree-days on the heating period. It has

already been calculated value Dd for St. Peters-

burg equal to 4110,9 °C•day/year;

24 – number of hours per day;

1000•1163 – coefficient for transfer of power of heat flow from watts to Gcal [14].

Calculations of the thickness of the insulation lay-er and the payback period is defined for warming the variants.The first and the second variants of winterizing do not differ from the point of their payback periods. The payback periods are cal-

culated according to the method [17] which do not take account of the following variables:

rise of the tariff on the central heating;

interest rates (in case a bank loan is a source of financing);

rates of discounting;

inflation rates [22]

This is the reason why the numbers describing payback period should be considered as a rough estimate.

The payback periods for the presented variants do not differ substantially. Functional relationship of the payback period and the heat transmission resistance of an external wall (for the 2d variant of winterization) is indicated on the Figure 4.

-

-

-

-

Figure 4: Dependence of the payback period on the reduced thermal resistance of external wall insulation

for the second option

The optimal choice is the winterization construc-tion (the thickness of heat insulation – 150 mil-limeters) that has the following characteristics:

reduced total thermal resistance – R = 2,77 (m2∙C)/W;

the payback period of the

winterization – T = 11,4 years [24].

Project of the reconstruction of the building with

winterizing the external walls with the use of

hinged vented façades (Figure 5).

•

•

CONCLUSION

External envelops of 5-store building social

educational services is not answerable to

standard requirements.

Value of defection calculate specific drain of

energy on heating of building from standart

requirements is - 9%. So, it is a building of Е class («Very low») on energy efficiency. Nec-essary such measures on hight of class of energy efficiencyas:

Modernization and automatization of ventila-tion system, heater system;

-

-

1)




Exchange of windows;

Rise of thermal properties of external envel-ops;

The elaboration of the measures to improve energy efficiency should be based on the re-sults of technical examination and economic calculations. In the research it is presumed that the basic indicator is the payback pe-riod of winterization. Decisions on financing measure that directed at the improvement of the energy efficiency shall be made only following the detailed analysis;

2)

3)

4)

The optimal variant of the heat insulation of the external walls that is appropriate for this type of the buildings;

The examined administrative building is typical from point of its construction and maintenance regime. Therefore, the con-clusion of this research can be considered applicable to the majority of frame modeled administrative buildings (constructed during the considered period).

5)

6)

Figure 5: Reconstruction project

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Cvetkovska, M., Knezevic, M., Rogac, M., (2012), Thermal insulation effects on energy efficiency of building structures, Civil and En-vironmental Engineering UGM, No. XXI/2, Vol. 5, 1209-1215.

Gagarin V.G., (2009), Metody ekonomichesk-ogo analiza povysheniya urovnya teplo-

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zashchity ograzhdayushchikh konstruktsiy zdaniya, AVOK, 1, 10-18.

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Dodoo, A., Gustavsson, L., Sathre, R., (2011), Building energy-efficiency standards in a life cycle primary energy perspective, Energy and Buildings, 43 (7), 1589-1597.

Escrivá-Escrivá, G., Álvarez-Bel, C., Peñal-vo-López, E., (2011), New indices to assess building energy efficiency at the use stage, Energy and Buildings, 43 (2-3), 476-484.

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Jovanović, B., Božanić, V., (2013), Educa-tion in the field of energy efficiency in Serbia - Survey results and analysis, Journal of Ap-plied Engineering Science, 11 (1), 15-22.

Matrosov, Y.A., Chao, M., Goldstein, D.B., (2000), Development, review, and imple-mentation of building energy codes in Rus-sia: History, process, and stakeholder roles, Proceedings ACEEE Summer Study on En-ergy Efficiency in Buildings, 9, 9.275-9.286.

Matrosov, Yu.A.,Norford, L.K., Opitz, M.W., Butovsky, I.N.,(1997), Standards for heating energy use in Russian buildings: A review and a report of recent progress, Energy and Buildings, 25 (3), 207-222.

Murgul, V., (2012), Povysheniye energoef-fektivnosti rekonstruiruyemykh zhilykh zdaniy istoricheskoy zastroyki Sankt-Peterburga, Arkhitekton: izvestiya vuzov, 4 (40), 54-62.

Nemova, D.V., Tarasova, D.S., Staritsyna, A.A., Nefedova A.V., (2013), Results of educational building’s inspection, Construction of Unique Buildings and Structures, 8 (13), 1-11.

Ramesh, T., Prakash, R., Shukla, K.K., (2010), Life cycle energy analysis of build-ings: An overview, Energy and Buildings, 42 (10), 1592-1600.

Sartori, I., Hestnes, A.G., (2007), Energy use in the life cycle of conventional and low-en-ergy buildings: A review paper, Energy and Buildings, 39 (3), 249-257.

Samarin O.D., (2010), Vliyaniye oriyentatsii osteklennykh fasadov na summarnoye ener-gopotrebleniye zhilykh zdaniy, Magazine of Civil Engineerin, 8(18), 16-20.

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Thermal Performance of the Buildings. SNiP 23-02-2003. The State Construction Com-mittee of the Russian Federation, The Cen-tral Institute for Type Designing Moscow.

Thermal Performance of the Buildings. Up-dated Version of SNiP 23-02-2003. SP 50.13330.2012 The Federal Center for Reg-ulations, Standardization, and Technical As-sessment of Conformity with Standards in the Construction Industry Moscow.

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45



OPTIMAL CROSS-SECTIONAL DESIGN FOR MINIMUM EMBODIED ENERGY

Dr Luisa María Gil Martín*Campus Universitario de Fuentenueva, University of Granada , Granada, Spain

Dr Enrique Hernández MontesCampus Universitario de Fuentenueva , University of Granada , Granada, Spain

* Campus Universitario de Fuentenueva, ,18071 Granada, Spain

[email protected]

In order to reduce the CO2 emission engineers and architects must optimize the use of materials,

particularly steel, making an optimal use of it. It is possible to guarantee the strength of the struc-

tural element reducing the amount of steel locating it properly at the cross-section and introducing a

higher control level at construction site

Key words: Sustainable construction, Embodied energy, Saving of steel

INTRODUCTION

Global warming due to greenhouse gases emis-sions is a worldwide problem. It is known that greenhouse gases are mainly sourced from the burning of fossil fuel being of all the gas emis-sions those CO

2 is by far the most important.

The problem relating to the global warming had become so important that 175 countries decided in 2005 in Kyoto (Protocol of Kyoto) decrease by 8% the greenhouse gases emissions during 2008 to 2010 compared to 1990 levels.

The steel is one of the most environmental care-ful products because of its high recycling rate and comparatively low quantities of energy required for its making. However, because the steel in-dustry has a strong dependence on fossil fuels as energy source and limestone for the purifica-tion of iron oxides, the amount of emission of CO

2 emitted during its fabrication process is very

large. Motivated by social and economic reasons steel plants had introduced modern technology to save energy and treat the waste generated during the production process. Despite these ac-tions, the environment problem associated with the greenhouse gases emissions remains the key issue in the international steel industry.

The steelmaker companies have the installa-tions necessaries to produce steel sheets start-ing from raw materials (mainly iron ore and coal). Quite a few of these processes involve very high temperatures or tremendous forces. All these energy-intensive processes have a significant impact on the environment. In the last years,

companies are looking for ways to reduce the environmental impact of its activities and to con-trol its processes more efficiently. These actions have involved huge costs for firms. However, the sustainability for the steel industry concerns not only to the production of this material but also to the introduction to a rational consumption pattern. In this sense, an adequate awareness of engineers focused on a more rational use of steel can significantly reduce the consumed amount of this material, with the consequent en-vironmental and economic benefits.

ENVIRONMENTAL COST OF STEEL

Carbon credits are one of the three mechanisms proposed in the Kyoto Protocol for reducing emis-sions that cause global warming or greenhouse gases (GHG). The GHG emission reductions are measured in terms of Certified Emission Reduc-tions (CER). Each CER equals one tonne of CO

2

that is allowed to emit into the atmosphere. This system tries to motivate to companies to con-trolling the regular emissions generated by their production processes. Since 2008, the system of the Community Emissions Trading Scheme (ETS), applies to the countries of the European Economic Area (Member States, Norway, Ice land and Liechtenstein). The ETS aims to help EU Member States meet their commitments to limit or reduce emissions of greenhouse gases cost-effectively, allowing to companies buy or sell emission allowances. A carbon credit entitles the holder to emit one tone of CO

2. Imposing a


cap on the total number of allowances is what creates scarcity in the market so companies that not emit or reduce the emission have benefits while had to pay if emissions are bigger than al-lowed.Accepting that the average carbon dioxide emis-sion is 2 Tons per tonne of steel, it is possible to estimate the environmental cost associated to the production of this material. In this paper the average value of 14 €/Ton of CO

2 emissions is

adopted and, in order to estimate the cost of the steel, has been accepted that the price of each ton of steel is 1 € and that the specific weight of steel is 78.5 kN/m3.

STEEL IN STRUCTURES

Until now, the main uses of steel have been in the transport, packaging and construction sectors. In the latter, i.e. civil engineering and architecture, the steel is usually used alone or in combination with concrete. In the second case, the steel is re-

sponsible for resisting tensile stresses while the concrete is placed in the compressed area of the cross section, in which the steel is susceptible to instabilities. In this paper is shown that an opti-mal distribution of steel in the cross-section can save very important amount of steel.

Reinforced concrete structure

The design of longitudinal reinforcement in rein-forced concrete structures is often made with the assistance of N–M interaction diagrams, which generally are presented only for symmetric rein-forcement. However, it is evident from RSD de-sign approaches [01, 02] that in some cases it is feasible and economically advantageous to use asymmetric reinforcement distributions.

RSD methodology consists in the consideration of all the possible solutions, for a design prob-lem, through the representation called RSD, as illustrated for a reinforced concrete section in Figure 1 [03].

Figure 1: Example of RSD for uniaxial bending

Recent work by the authors has emphasized a unique solution strategy in which reinforcement solutions are obtained as a function of the neutral axis depth, allowing optimal reinforcement solu-tions to be characterized and used for design. The resulting reinforcement distributions gener-ally are not symmetric, but conform to building code requirements and may result in significant savings of reinforcement, and thus advance the aims of sustainability in construction. In one in-stance, Reinforcement Sizing Diagrams are ap-plied to the design of sections subjected to uni-axial bending in conjunction with axial load [03].

Although this non-symmetrical reinforcement in elements subjected to both bending moment and compression load represents a major advance in the state of the art of reinforced concrete, its ap-plicability to piles of structures is very limited due to the random nature of the horizontal forces due to wind and earthquake. In order to account for the possible reversal of sign of the bending mo-ments symmetrically reinforced piles have to be disposed. On the contrary, in situations in which such reversal of sign of the bending moment is not possible, a non-symmetrical reinforcement of the cross-section of concrete can save a sig-

Dr Luisa María Gil Martín-Optimal cross-sectional design for minimum

embodied energy


nificant quantity of steel. This situation happens in earth retention walls, in which the tensile zone will be always placed next to the soil because the unidirectional action of passive earth pressures.

In cities is very frequent the use of cut and cover excavation systems for projects such as sub-ways, depressed rail and road bed. In these cases a temporary decking is included resting on the top of the retaining wall to permit traffic to use the space overhead while the construction process continue below (Figure 4). In such situ-ations, the cast in place cantilever wall is very often constructed by circular piers of reinforced concrete because the pier foundations are less costly to construct than continuous wall founda-

tions, simply due to the fact they use less mate-rial.

Circular pier reinforced with steel cages

Walls of piles (Figure 2.a), frequently used in un-derground construction, are routinely constructed using symmetric reinforcement (Figure 2.b). De-sign solutions for circular sections obtained with available computer programs and charts are built on the premise that the longitudinal reinforcement consists of a uniform bar diameter (ϕ) distributed

evenly around the perimeter of the section, at a

constant spacing. Nevertheless It has been shown

that this reinforcement can be optimized [04, 05].

Figure 2: a. Secant wall construction (adapted from an archive of Land Transportation Authority, USA), b. Types of bored piles walls whit Traditional longitudinal reinforcement

In earth retaining structures, in light of the rela-

tively insignificant axial compression sustained

and because the unidirectional action of passive

earth pressures results in a well defined mono-

tonic direction of action for the design flexural

moment at the critical cross-section - with no

transverse components -, an alternative reinforc-

ing arrangements such as those shown in Figure

3 may be more appropriate.

A pier with a diameter of 1 m will be considered

in this paper. The conventional design utilized

twenty ϕ 25 bars for longitudinal reinforcement,

with circular hoops of ϕ 8 @ 300 mm. The de-

sign axial force is approximately zero. Steel re-

inforcement was B-500-S having a characteris-

tic strength of 500 MPa. Concrete, C-25, had a

nominal compressive strength of 25 MPa. The

total area of initially projected longitudinal rein-


embodied energy


Figure 3: Piers of retaining wall a) Initial reinforcement b) Optimized reinforcement

forcement (twenty ϕ 25) was 9817 mm2 or 1.25

% of the gross area. Initial and optimized rein-

forcement locations are shown in Figure 3.

As shows in Table 1, reinforcement savings of

44 % can be obtained when two different bar di-

ameters were used as shown in Figure 3(b), with

the same flexural strength that the traditional

designed pier -with symmetrically arranged lon-

gitudinal reinforcement (Figure 3(a)). This reduc-

tion in weight of steel implies a reduction in both

the cost of transportation and the machinery for

erection (cranes) of the reinforcement cages.

In Figure 4 the interaction diagrams for both tra-

ditional and optimized piers in Table 1 have been

represented. Figure 4 show that both piers have

the same capacity in pure bending. So, Table 1

and Figure 4 show that the design bending mo-

ment can be carried adequately by cross sec-

tions containing alternative reinforcing arrange-

ments such as this shown in Figure 3.b with an

important saving in the use of steel reinforce-

ment and without any loss of stiffness or strength

properties. The primary advantage of those al-

ternatives being the significant economy in rein-

forcing steel, they incur great savings in terms of

embodied energy and cost as compared with the

conventional symmetrical solution (Figure 3.a).

Solution Bar composition Area of steel (mm2) Mu (kN•m)

Initial –traditional- 20 ϕ 25 9817.5 1712

Optimization of the

reinforcement

6 ϕ 32 @ 64 mm

+ 9 ϕ 10 @ 270mm5532.3 1722

Table 1: Longitudinal reinforcement of piles. Initial and optimized solutions pure bending

Figure 4 – Interaction N-M diagrams

48 , 274


embodied energy


Circular pier reinforced with embedded I shapes

Sometime, instead of reinforcing the piles with steel rebar, a steel I-shape is introduced in the hole before pouring the concrete. This procedure is more common in the case of secant pile walls, in witch piles overlap to each other. In this case, applying a similar procedure than in the previ-ous case, it is possible an optimization of the amount of steel. An important reduction of the embedded steel cross-section can be obtained without compromising the strength of the retain-ing wall pile. In the optimization procedure has been admitted that the centre of the web of the embedded steel shape coincides with the centre of the circle of the pier. A pier with a diameter of 600 mm has been studied. The conventional

design used an IPE500 embedded shape. The design axial force is approximately zero. Steel was S235 having a characteristic strength of 235 MPa. Concrete C-30 had a nominal compressive strength of 30 MPa. The total area of steel initial-ly embedded was 11173.6 mm2. Similarly to the case of piers reinforced with cages of steel, an optimization procedure had been implemented to reduce the area of embedded steel in piers subjected to pure bending conditions, i.e. when the design axial force is approximately zero. In this example, the thickness of the web of the optimized embedded shapes had been fixed equal to the corresponding value of the IPE-500 shape. In Figure 5, the optimized cross-section steel shapes, dimensions and areas are summa-rized.

Figure 5: Initial (IPE 500 I-Shape) and optimized embedded steel shapes in circular piers of retaining walls.

In this figure: bf is the width of the flange, t

f is the thickness of the flange, h

w is the height of the web, t

f is the

thickness of the web and As is the area of the embedded steel cross-section

The interaction diagrams of the traditional and op-timized piers with embedded steel are represent-ed in Figure 6. This figure shows that the three solutions have the same pure bending strength while the optimized proposed solutions involve an important reduction of the amount of steel. In Figure 6 the steel contribution ratio δ (defined in

Eurocode 4 [8]) has also been indicated.

STEEL STRUCTURES

The RSD technique can also be applied to the

proportioning of steel cross-sections [06, 07]. For

the design of a steel cross-section subjected to

combined loads N and M also an infinite number

of solutions exist. These solutions can be graphi-

cally represented to make easier the choosing

of the most appropriate, similarly to the RSD

representation for RC sections (Figure 1). In the

optimization procedure of steel members, both

strength and buckling requirements established

in EC3 [09] were considered. The optimized pro-

cedure was applied to both compact and slender

cross section steel.

CONCLUSION

In order to reduce the CO2 emission engineers

and architects must optimize the use of materi-

als, particularly steel, making an optimal use of

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embodied energy


this material. Especial attention has to be paid to the embodied energy associated with each one of the materials, i.e. steel and concrete. It is pos-sible to guarantee the strength of the structural

element reducing the amount of steel locating it properly at the cross-section and introducing a higher control level at jobsite.

Figure 6: Interaction N-M diagrams

REFERENCES

E. Hernández-Montes, L.M. Gil-Martín, M. Pasadas-Fernández, M. Aschheim, “Theo-rem of Optimal Reinforcement for Reinforced Concrete Cross Sections”. Structural and Multidisciplinary Optimization”, Vol. 36, 2008, p. 509-521.

Eurocode 3. European Committee for Stan-darization. prEN1993-1-1. Eurocode 3. Design of steel structures. Part 1.1: General rules and rules for buildings. Brussels; 2005.

Eurocode 4. European Committee for Stan-darization. prEN1993-1-1. Eurocode 4. De-sign of composite steel and concrete struc-tures – Part 1-1: General rules and rules for buildings. Brussels; 2004.

J.F. Carbonell-Márquez, L: M. Gil-Martín, E. Hernández-Montes, “Strength design optimi-zation of structural steel members accord-ing to Eurocode3 “. Journal of Constructional Steel Research, Vol. 80, 2013, p. 213- 223.

L.M. Gil-Martín, E. Hernández-Montes, M. Aschheim, “Optimal reinforcement of RC columns for biaxial bending“. Materials and

1)

2)

3)

4)

5)

Structures/Materiaux Et Constructions, Vol. 43(9), p.1245-1256.

L.M. Gil-Martín, E. Hernández-Montes, M. Aschheim, “Optimization of piers for retaining walls”. Structural and Multidisciplinary Optimi-zation. Vol. 41 (6), June 2010, p. 979-987.

L.M. Gil-Martín, E. Hernández-Montes, M. Shin, M. Aschheim, “Developments in exca-vation bracing systems”. Tunnelling and Un-derground Space Technology, Vol. 31, 2012, p. 107-116.

L.M. Gil-Martín, M. Aschheim, E. Hernández-Montes, “Proportioning of Steel Beam-Col-umn Members Based on RSD Optimization Methodology“. Engineering Structures. Vol. 30, 2008, p. 3003-3013.

L.M. Gil-Martin, M. Aschheim, E. Hernandez-Montes, ”Proportioning of steel beam-column members based on RSD optimization meth-odology”. Engineering Structures, Vol. 30(11), 2008, p. 3003-3013.

6)

7)

8)

9)


Paper ready for publicatuion: 15.03.2014.

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embodied energy

RACKING RESISTANCE OF PREFABRICATED TIMBER-GLASS WALL ELEMENTS

Importance of building large-size glazing into timber structures has significantly grown over the last

decade. This was one of the major reasons for carrying out the presented experimental research

on timber structures with a fixed glazing placed in the external sides or in the middle of the timber-

frame wall elements. Timber frame, to which glass pane is directly attached, forms the composite

wall element, which contributes to stability of the entire system with its load capacity. Different types

of adhesives with specific characteristics were used and they consequently caused different impacts

on a wall composite. Both concepts, with bilateral glass as well as single glass lining in the middle

of profile, are presented.

Key words: Timber, Glass, Resistance, Stability, Experiments, Monotonic tests



Dr Miroslav Premrov*Faculty of Civil Engineering, University of Maribor , Maribor, Slovenia

Boštjan BerKager hiša DOO, Ptuj, Slovenia

Dr Andrej ŠtrukeljFaculty of Civil Engineering, University of Maribor , Maribor, Slovenia

* Faculty of Civil Engineering, Smetanova ul. 17, SI – 2000 Maribor, Slovenia

[email protected]

INTRODUCTION

Timber is a non-demanding material for prefab-rication due to its organic structure and low den-sity. It is also an ideal construction material from the viewpoint of energy efficiency since CO2 emissions in production of a timber element tend to be approximately two times lower that those present in manufacturing an equivalent brick el-ement, three times lower than in the case of a concrete element and six times lower than CO2 emissions in steel element production. Neverthe-less, timber achieved recognition as one of the oldest building materials in different countries worldwide. On the other hand, the grey energy consumption of glass is very high (15.9 MJ/kg), greater even as by brick or concrete, thus the energy aspect of glass was often treated as a weak point in the past. However, in the last few decades glass has become one of the main driv-ers of technical development for the purposes of the building industry. Owing to significantly im-proved its optical and especially energy related, i.e insulating properties, glass has become an ever more widely used material and is no longer solely responsible for daylighting or the transpar-ency of the building only. Another important nov-elty arising from the phenomenon of increasing

the size of glazing surfaces in modern buildings is taking the load bearing function of glass into account, where its integration with other build-ing materials plays a vital role. Dynamic evolu-tion of the glazing in the last 40 years resulted in insulating glass products with highly improved physical and strength properties, suitable for ap-plication in contemporary energy-efficient build-ings, not only as material responsible for solar gains and daylighting, but also as a component of structural resisting elements.

With suitable technological development and ap-propriate use, timber and glass are nowadays becoming essential construction materials as far as the energy efficiency is concerned. Integra-tion of large and properly oriented glazed areas into timber structures represents a great poten-tial for the construction of environment-friendly and energy-efficient buildings. With respect to the energy related facts, a major part of the glazing needs to be installed in the south-oriented façade for the purpose of better energy performance of a building, which leads to specific technical chal-lenges in the field of structural behaviour of the load bearing wall elements with an enlarged glaz-ing size, Žegarac and Premrov [01]. Even though energy-efficient, such construction systems can be extremely problematic when the building is


exposed to horizontal loads. As a consequence, resisting problems can occur in timber-glass load-bearing wall elements exposed to havy horizontal actions like earthquake or wind.

GLASS IN PREFABRICATED TIMBER-FRAME WALLS

Timber is commonly associated with lightweight construction although it is ubiquitous as a build-ing material. Recently, there are many argu-ments for timber-frame residential buildings such as built-in materials show environmental excel-lence, lower energy consumption while prepar-ing built-in materials and as one of the most im-portant the speed of construction. Due to high degree of prefabricated elements timber-frame buildings are built in essential shorter period of

a) b)

time when compared to conventional brick build-ing techniques. It also means that during con-struction the building is exposed to inconvenient weather conditions only shortly.

There are four main construction systems of timber-frame residential buildings: a.) classical post and beam system, b.) classical balloon-frame system, c.) cell system, d.) prefabricated timber-frame panel system. In our study we will be dedicated to the prefabricated timber-frame panel system, originates from the Scandinavian-American construction methods, i.e. balloon-frame and platform-frame construction types whose assembly-works take place on-site. We can distinguish between an old single-panel wall system (Figure 1a) and in this time widely used macro-panel wall system (Figure 1b).

In the both structural systems the timber-frame walls as main vertical bearing capacity elements of usually typical dimensions with a width of b = 1250 mm (single-panel) or b = n•1250 mm (mac-ro-panel) and a height of h = 2500 – 2600 mm are composed of a timber frame and of sheets of board-material fixed to the both sides of the tim-ber frame. In the macro-panel structural system the wall elements with a total length of up to 12.5 metres are now entirely produced in a factory.

There are many types of panel sheet products available which may have some structural ca-pacity such as wood-based materials or fibre-

plaster boards (FPB). Between the timber studs a thermo-insulation material is inserted which thickness depends on the type of the wall in a sense to improve the thermal properties of the external walls. The influence of different types of the sheathing boards is already deeply analysed and discussed in Premrov and Kuhta [02].

However, the main contribution of the presented research is in replacing the classical sheats with the glass panes, as it is schematically presented in Figure 2. One of the main drawbacks of glass used as a load bearing material lies in its being a relatively brittle material with mostly a signifi-cantly low degree of post-cracking resistance.

Figure 1: Prefabricated timber-frame systems; a.) single-panel, b.) macro-panel.

52 , 275

Dr Miroslav Premrov- Racking resistance of prefabricated

timber-glass wall elements


On the other hand, glass has a high modulus of elasticity of approximately 70 GPa, which is a value about 6-times higher than that of softwood in the grain direction, although 3-times lower than that of steel and equal to that of aluminium. Thus we can claim that glass is relatively stiff mate-

Figure 2: Timber-glass prefabricated walls - replacing classical sheathing boards with glass panes

rial and that properly inserted glass elements can significantly contribute to the stiffness of the structure. A difficulty still remaining is seen in the behaviour of glass, which is almost linear-elastic until failure.

It is consequently of utmost importance for ad-hesives to assure resistance and a high range of ductility of such composed load bearing ele-ments with quite different material properties, simultaneously to finding balance between strength and deformability. Adhesives must also allow for expansion and shrinkage of timber, ac-cording to loading and humidity variations, Cruz and Pequeno [03]. According to Cruz adhesives used in timber-glass composites can be clas-sified into three main groups: a.) Highly resis-tant and insufficiently flexible adhesives – rigid adhesives (acrylate, epoxy); b.) Highly flexible adhesives, yet insufficiently resistant to loading – elastic adhesives (silicone); c.) Adhesives that balance both key factors - strength and flexibility – semi-rigid adhesives (polyurethane, superflex polymers).

EXPERIMENTAL STUDY

We conducted research on the lateral load-bear-ing capacity of the timber-glass wall element with a two-sided glass sheathing glued to the outer side of the timber frame (Concept 1 in Figure 3b) and a single glass pane placed in the center of the cross section (Concept 2 in Figure 3b). A number of stud-ies on combining glass with timber and those on the in-plane load-bearing capacity of glass panes have been so far carried out the Technical Univer-sity of Vienna in Hochhauser et al. [4], which will be of assistance in the comparison with our experi-mental results. In their proposal the glazing placed on the external side of the timber frame was not directly glued to the timber frame but bonded with adhesives to the special substructure (Figure 3a) which is fixed with bolts to the external side of the timber frame. The most important technological advantage of such type of connection is a relatively simple replacement of the glazing replacement in the case of its breakage.

53, 275




Figure 3: a) HGV concept, b) Slovenian concepts of connecting the glass pane

to the timber frame (direct connection)

a) b)

The test specimens consisted of a timber frame with the outside edges measuring 1250/2640 mm (Figure 4a), which used to be a standard size of wall panels tested in previous studies where a different sheathing material was used, ref. [03] to [06]. Vertical studs were composed of rectan-

gular 90/90 mm timber elements with the size of horizontal girders being 90/80 mm. During the testing process the panels were rotated by 90° and fixed with the left vertical stud via three coil bars Φ16 into the stirrup consisting of two steel

plates, as shown in Figure 4b.

Figure 4: a) Cross-section of the test samples; b) Position of the test sample during

the loading procedure

54 , 275




Timber frame elements in both concepts were made of wood with a strength grade C22, glass panes consisted of toughened ESG glass and the adhesive used in the timber-glass joint was a two-component silicone adhesive type Ködi-glaze S (Concept 1), produced by Kömmerling [5]. In the second case (Concept 2), polyure-thane (Kömmerling [06]) and epoxy adhesives (Kömmerling [07]) were additionally used, sili-cone was the same. Material properties of tim-ber with a strength grade C22 were taken from EN 338:2003, with properties of thermally tough-ened glass being taken from EN 572-1:2004 and EN 12150-1:2000.

The results of all specimen groups are given in Figure 5 which shows the normalized values of vertical displacements (w) relative to force F, sep-

arately for each specimen. In specimens groups ST- O and ST-E, we witnessed an explosive col-lapse of a glass pane. In specimens groups ST-S and ST-P a failure occurred due to collapse of the upper left corner of the timber frame. Results of ST testing group were compared with testing groups of wall panels with different sheathing material by Premrov and Kuhta [08]. The timber-glass wall elements were labelled as ST, while the labels of other test specimens mean the fol-lowing: G2 – single FPB sheathing with a span of s = 75 mm between the staples (n = 4), G2D – double FPB sheathing with a span of s = 75 mm between the staples (n = 1), G2O – single OSB sheathing with a span of s = 75 mm be-tween the staples (n = 3).

Figure 5: F-w diagrams of the test specimens with different types of the sheathing materials

Load-carrying capacity and stiffness of group ST-E can be compared with G2O. Almost identi-cal stiffness and strength can be seen in groups ST-S and ST-P. Furthermore, it is clear that the specimens G2, G2D and G2O behave almost linear-elastic until the appearance of the first cracks. The continuation of the test caused re-ducing of stiffness G2 and G2D due to increased slips in the connection planes as a result of fas-teners plastification.

CONCLUSION

The results of the experimental researches were positive surprise since we did not expect such high values of failure forces, which are compara-ble to those of experimental researches including the usual sheathing materials (FPB, OSB). Nev-ertheless, the racking stiffness of timber-glass wall panels and softer adhesives (ST-O, SP-S, SP-P) was significantly lower (with the exception of the ST-E), as in the conventional sheathing material. In practice this would mean difficulty in achieving serviceability limit state. The reason

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for this phenomenon is too flexible contact be-tween the glass pane and timber frame. Taking into account the significantly different mechani-cal properties of these materials, especially at high temperature load, we conclude that flexible joints should be used.

ACKNOWLEDGEMENTS

The support of the companies Kager hiša, Re-flex and Sika Slovenia who donated the mate-rials needed for the experiments is gratefully acknowledged. The research work is part of the project LBTGC selected on the international WoodWisdom-Net and fundad by the MIZŠ.

LITERATURE

Cruz P., Pequeno J., “Timber-Glass Compos-ite Structural Panels: Experimental Studies & Architectural Applications”, Conference on Architectural and Structural Applications of Glass, Delft University of Technology, Facul-ty of Architecture, Delft, Netherlands, 2007.

Hochhauser W., Winter W., Kreher K., “Holz-Glas-Verbundkonstruktionen - State of the Art, Forschungsbericht, Studentische Arbe-iten”, Technische Universitat Wien, Institut fur Architekturwissenschaften Tragwerkspla-nung und Ingenieurholzbau, 2011.

1)

2)

Kömmerling, “Product Information Ködiglaze P - Special adhesive for bonding insulating glass units into the window sash”, 2008.

Kömmerling, “Product Information Ködiglaze S - Special adhesive for structural and direct glazing”, 2008.

Kömmerling, “Product Information Körapox 558 - Two component reaction adhesive for bonding of metals, for example steel or alu-minium to each other”, 2011.

Premrov M., Kuhta M., “Experimental Analysis on Behaviour of Timber-Framed Walls with Different Types of Sheathing Boards”.,Construction Materials and Engi-neering, Nova Science Publishers, 2010.

Premrov M., Kuhta M., “Influence of fasten-ers disposition on behavior of timber-framed walls with single fibre-plaster sheathing boards”, Construction and Building Materi-als, 2009, vol. 2, iss. 7, pp. 2688-2693.

Žegarac Leskovar V., Premrov M., “An ap-proach in architectural design of energy-ef-ficient timber buildings with a focus on the optimal glazing size in the south-oriented fa-çade”, Energy and Buildings, 2011, vol. 43, iss. 12, pp. 3410-3418.

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57

Anka Starčev-Ćurčin*Faculty of Technical Sciences, University of Novi Sad, Novi Sad, Serbia

Dr Đorđe LađinovićFaculty of Technical Sciences, University of Novi Sad, Novi Sad, Serbia

Aleksandra RadujkovićFaculty of Technical Sciences, University of Novi Sad, Novi Sad, Serbia

Andrija RašetaFaculty of Technical Sciences, University of Novi Sad, Novi Sad, Serbia

CAPACITY DESIGN OF RC MULTI-STOREY FRAME ACCORDING TO EN 1998-1


Professional Paper

The method of capacity design requires the ductility of reinforced concrete load-bearing elements

and provides the beam plasticity mechanism for a structure to absorb a significant seismic energy.

Indeterminate static systems are particularly suitable, where an indefinite number of static indeter-

minacy determines the number of plastic hinges being forming, thus achieving favourable energy

dissipation. In this paper, reinforced concrete five-storey frame is designed for two ductility classes

according to the regulations EN1992-1-1 and EN1998-1.

Key words: Capacity design, Reinforced concrete frame, Ductility, Plastic hinges

* Faculty of Technical Science, Trg Dositeja Obradovića 6, 21000 Novi Sad, Serbia [email protected]

INTRODUCTION

In the exploitation phase, due to the effect of gravity loads, bearing structure remains within the linear elastic behaviour of materials [1]. Due to the effect of the seismic load, bearing ele-ments exceed the nonlinear work domain of ma-terials [02].

The difference of the aforementioned loads, in the reinforced-concrete structures, may be reflected in the fact that, for example, in the bending ele-ment for the case of normal loads, compressed and tensioned zones over the intersection height remain unchanged, while during the seismic load multiple changes may occur in the said zones. Then, the shear forces in beams, due to the effect of the gravity load, cause slope cracks in one di-rection, while due to seismic loads, slope cracks occur in two perpendicular directions. Adhesion anchorage of the longitudinal reinforcement, during the normal loads, does not change the stress direction, but during the action of seismic loads the stress direction is constantly changed. Increased bending capacity in the structures due to seismic loads may increase shear forces and cause undesirable transverse fracture.

These differences lead to different approaches in designing and detailing of structural elements

when the impact of seismic loads is introduced in the design.

CAPACITY DESIGN REGULATIONS ACCORDING TO EN1998-1

During the action of seismic load, the structure response depends on the behaviour of vertical load-bearing elements. In this paper, the empha-sis will be placed on reinforced concrete frame structures.

For reinforced concrete structures according to EN1998-1, [02], the method of programmed be-haviour of the load-bearing elements (method of capacity design) is used. It includes calculations and detailing in the design of a structure.The method requires selecting the places in the bear-ing structure in which the plastification will occur in order to achieve a favourable plastic mecha-nism. Selected places are dimensioned and de-tailed so as to reach the desired degree of duc-tility. Other parts of the structure are designed with extra load capacity (capacity) to remain in the elastic range of work materials. In the for-mation of plastic hinges in multi-storey buildings, the beam mechanism of the plastification in the structure is acceptable, and plastic hinges occur in the frame beams and columns in the base.


The creation of the plastic hinges in the columns results in a relatively large rotation of the struc-ture which makes that kind of mechanism unac-ceptable as compared to the beam mechanism.

In order to avoid the plastic hinges in columns, in frame structures exposed to the effects of seismic loads, during the design, the principle that the column bending capacity is greater than the capacity of the beam bending (the “strong columns-weak beams”) must be fulfilled. In the beam-column joint, it is difficult to provide ductile behaviour; therefore, outside the inner zone of the frame joints, the formation of plastic hinges must be achieved by detailing.

NUMERICAL EXAMPLE

Five-storey structure is designed according to EN1992-1-1 and EN1998-1 for two ductil-ity classes, medium DCM and high DCH. For the analysis, software packages TOWER7 and SAP2000 V14-2 have been used.

The base of the analysed five-storey structure and the cross-section of the building are shown in Figure 1. The structure is symmetrical in both directions, with the range of 3x5m and the storey height of 3m. Slab thickness is 15cm, cross-sec-tional dimensions of beams are 30/45cm, while the dimensions of the columns are 45/45cm.

Figure 1: Floor plan and the cross-section of the structure

As the structure satisfies the criteria of the regu-larity basis, it can be analyzed as 3D or as 2D structure, [02]. Numerical analysis uses the planar model of the inner frame with the T-sec-tion beam and the effective width of 170cm. All columns are fixed in rigid foundation. In order to consider the influence of cracks, flexion and shear properties of the elements are reduced to the half of the uncracked section values. For the ductility class DCM concrete class C25/30 is used, and for the ductility class DCH concrete class C35/45 is used, with the Poisson ratio v =0 (cracked concrete), and steel S500 class C. In order to satisfy the condition of anchoring and continuing the longitudinal reinforcement beam bars in the node, [02], and not to increase the dimensions of the columns, the higher concrete class for the frame of the ductility class DCH has been adopted. The permanent load “G” includes the self weight of the elements and the dead add-ed permanent load in the amount of 2.5kN/m2.

The imposed load “Q” for the building category B, according to [03], is taken as equally distrib-uted with 2.5kN/m2 intensity. Moment diagrams of permanent and imposed loads are shown in Figure 2.

The seismic action is represented by the hori-zontal elastic response spectrum of type 1 and the soil category C with a maximum acceleration of soil 0.2g. Values of the period and soil factor that describe the shape of the elastic response spectrum are TB=0.2s, TC=0.6s, TD=2s, S=1.15, and for the damping correction factor is η=1. The

building is classified as a building of significant

class II and the importance factor is y =1.

Elastic analysis is carried out based on the de-

sign response spectrum, which is reduced in

comparison to the elastic spectrum using the be-

haviour factor q. The value of the design seismic

load determined for the ductility class DCM is

q=3.9 and for the ductility class DCH is q=5.85.

58

Anka Starčev-Ćurčin- Capacity design of RC multi-storey frame according to EN-1998-1

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Figure 2: Moment diagrams of permanent and imposed loads

For the design of the forces of the seismic im-pact, the multimodal spectral analysis is applied and the impacts of the first two vibration modes are being considered, [02]. Inertial effects of the seismic design action are calculated based on the weight associated with all gravity loads (permanent and imposed) that occur in the cor-responding combined actions of roof G+0.3Q, and for other stories G+0.15Q, [4]. The mass of the top storey of the frame structure is 53.57t,

and for other stories is 54.2t. The total mass of the designed frame structure is 271.65t. The shape and values of moments due to seis-mic forces E and -E for vibration periods of two dominant tones, for the first T1= 0.8288s and the second T2= 0.2663s for ductility class DCM, and for vibration periods of two domi-nant tones, for the first T1= 0.791s and the second T2= 0.254s for ductility class DCH, are shown in Figure 3.

Figure 3: Moments due to seismic forces E and –E, for DCM and DCH

According to EN 1992-1-1, [01] based on the force en-velope of the load combination, the observed frames are dimensioned. Regulative EN 1998-1, [02], for both classes of ductility, DCM and DCH, requires the

design regulative for the ultimate limit state, as well as detailing and fulfilling the required bending and shear capacity, and local ductility in beams and columns of dimensioned elements of the frame.

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Fulfilment of the local ductility, which implies the fulfilment of the maximum value of the tensioned and compressed reinforcement coefficients, in both ductility classes, demands for the increase of the compressed reinforcement in the support-ing sections. Regulative on the local ductility, [2], reduces the distance between the transverse re-inforcement, stirrups, in the ductility class DCH. Based on these adjustments that are required to control capacity and design details, the new amounts of longitudinal and transverse rein-forcement are adopted, as shown in Figure 4 for the ductility class DCM and in Figure 5 for the ductility class DCH.

Figure 4: Addopted reinforcement for DCM according to EN1998-1: a) beam-support, b) beam- field

and c) column

Figure 5: Addopted reinforcement for DCH according to EN1998-1: a) beam-support, b) beam- field

and c) column

The amount of reinforcement required by EN1992-1-1 does not fulfil the rules for the capacity con-trol of the local and global ductility according to EN1998-1. In the frame of the ductility class DCM, the amount of the support compressed reinforce-ment is increased from 3Ø16 [6.03cm2] to 4Ø16 [8.04cm2], and in the frame of the ductility class DCH from 3Ø14 [4.62cm2] to 5Ø14 [7.7cm2]. The change in the amount of transverse reinforcement occurs in the frame of the ductility class DCH. The amount of stirrups is increased from Ø8/10 [5cm2/m’] to Ø8/8 [6.25cm2/m’] in the beam-support, and in the beam-field from Ø8/20 [2.5cm2/m’] to Ø8/15 [3.33cm2/m’]. In the column the amount is increased from Ø8/10 [5cm2/m’] to Ø8/7.5 [6.67cm2/m’].

Nonlinear static “pushover” analysis

For nonlinear analysis, the cross-sections are pre-sented as: confined part of the section (the core), unconfined part of the section (a protective layer of concrete to reinforcement) and reinforcement. Relation stress-strain for unconfined and con-fined part of the cross-section for beam-support and column, for the concrete classes C25/30 and C35/45 and for the steel S500 are shown in Figure 6.Target displacement of ductility class DCM frame for the modal pattern of the forces is D

t=10.75cm,

and for the uniform pattern is Dt=9.21cm. In

the frame of the ductility class DCH, for the modal pattern of forces, target displacement is D

t=10.52cm, and for the uniform pattern is

Dt=8.93cm. In Figure 7, the curves of the capac-

ity for specific target displacement are shown.

Figure 6: Relation stress-strain for conncrete C25/30 and C35/45 and for steel S500

It is observed the higher shear forces are in the grounds of the building for the uniform pattern.The interstorey drift of the frames for ductility classes DCM and DCH due to the effect of the modal and uniform pattern are shown in Figure 8.Structural behaviour estimate based on ‘’push-over’’ analysis in the frame of the ductility class

DCM, for the modal pattern of forces, is deter-mined by the value of the overstrength ratio αu/α1

which is 1.35, and for the uniform pattern of forces,

αu/α

1 value is 1.38. For the frame of the ductility

class DCH αu/α

1 value is 1.42 for the modal pat-

tern of forces and for the uniform pattern of forces

arranged by height frame, αu/α

1 value is 1.52.

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Results oh the ‘’pushover’’ analysis show that, for the adopted characteristics of the frame, there is an addi-tional capacity, because the adopted value α

u/α

1=1.3,

at the beginning of the design, is lower than the value

obtained from the αu/α

1 of the ‘’pushover’’ analysis.

For the target displacement, during the modal

and uniform pattern of the forces, the formation

of the plastic hinges is shown in Figure 9.

Figure 7: Capacity curve of the frame for the ductility classes DCM and DCH

Figure 8: Interstorey drift of the frames for the classes DCM and DCH

Figure 9: Formation of the plastic hinges for a) DCM and b) DCH for target displacement

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The development of the plastic hinges mecha-nism in both structures is favorable. Plastic hing-es are formed at the ends of beams and columns in the base. In both structures plastic hinges oc-cur at the same places and in the same number. There was a difference only in the larger plastifi-cation of the hinges of the fourth-floor beams in the structure of the ductility class DCH.

CONCLUSION

The correct behaviour of reinforced concrete structures, i.e. the acceptance of the seismic energy without significant damage to the load-bearing elements at higher intensities of earth-quakes, involves the selection of the structure, which is reflected in its simplicity, and its sym-metry both at the base and in the height, as well as its load capacity, stiffness and ductility.

The analysis of the five-storey reinforced concrete frame shows that sections designed according to EN1992-1-1, [01], do not fulfil the regulative required by EN1998-1, [02], for both classes of ductility, and therefore they have to be revised and new required reinforcement amounts have to be adopted, Figures 4 and 5. In the frame of the ductility class DCM, the amount of longitudi-nal reinforcement is increased for 33%, and in the frame of the class DCH for 66%. The change in the amount of transverse reinforcement oc-curs in the ductility class DCH which is increased in beams for 25%, and in columns for 33%.

Conditions required by the ductility class DCH are stricter than the conditions required by the ductility class DCM. Seismic forces at DCH are smaller but the control of the capacity and ductil-ity of the section is stricter. Comparing the re-inforced sections of both ductility classes, it is noted that, as expected, the larger amount of reinforcement is in the class DCM, while it is lower in the ductility class DCH. However, the demanded increase of the material quality led to the greater capacity in the ductility class DCH at the expense of the reduced ductility.

Based on the results of the ‘’pushover’’ analysis, it is shown that the capacity curves for both duc-tility classes had no significant differences as a result of the relationship of strength and ductility of the frame elements on the basis of the adopted amount of reinforcement and material character-istics. For adopted characteristics of the frame, there is an additional structural capacity that can be seen from the values of multiplication factors

obtained from the ‘’pushover’’ analysis. The ar-rangement of the plastic hinge formation, Figure 9, shows a favourable development of the plastic hinge mechanism since they are formed at the ends of beams and columns in the base in both structures of two ductility classes.

The results show that, for the analysed reinforced concrete frame, in the case of an earthquake of moderate intensity, there is no significant differ-ence in choosing between ductility classes DCM and DCH, [05]. The considered structures and seismic effects show satisfactory capacity val-ues, stiffness and ductility, and the results indi-cate that the reinforced concrete frame, in which the bearing elements are designed according to EN1998-1, [02], can accept the given seismic forces.

ACKNOWLEDGEMENTS

The work has been done within the scientific research project TR 36043 “Development and application of a comprehensive approach to the design of new and safety assessment of exist-ing structures for seismic risk reduction in Ser-bia”, which is funded by the Ministry of Science of Serbia.

REFERENCES

EN1992-1-1:2004, Proračun betonskih

konstrukcija, deo 1-1: Opšta pravila i

pravila za zgrade. Beograd: Građevinski

fakultet Univerziteta u Beogradu, 2006.

EN1998-1:2004, Proračun seizmički ot-

pornih konstrukcija, deo 1: Opšta pravila,

seizmička dejstva i pravila za zgrade. Beo-

grad: Građevinski fakultet Univerziteta u

Beogradu, 2009.

EN1991-1-1 Evrokod 1: Dejstva na kon-

strukcije. Deo 1-1: Zapreminske težine,

Sopstvena težina, Korisna opterećenja za

zgrade. Beograd, novembar 2009.

EN1990:2002, Osnove proračuna kon-

strukcija, Beograd: Građevinski fakultet

Univerziteta u Beogradu.

Fardis M. Seismic Design, Assessment and

Retrofitting of Concrete Buildings, Based on

EN-Eurocode8, Spinger Dordrecht Heidel-

berg London New York, 2009.

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Marijana Lazarevska*Faculty of Civil Engineering, University of Skopje, Skopje, Macedonia

Milivoje MilanovićState University of Novi Pazar, Novi Pazar, Serbia

Dr Miloš KneževićFaculty of Civil Engineering, University of Podgorica, Podgorica, Montenegro

Dr Meri CvetkovskaFaculty of Civil Engineering, University of Skopje, Skopje, Macedonia

Ana Trombeva GavriloskaFaculty of Civil Engineering, University of Skopje, Skopje, Macedonia

Dr Todorka SamadzioskaFaculty of Architecture, University of Skopje, Skopje, Macedonia

AN ARTIFICIAL NEURAL NETWORK PREDICTION MODEL FOR FIRE RESISTANCE OF

COMPOSITE COLUMNS



* Faculty of Civil Engineering, Bulevar Partizanski odredi 24, 560 Skopje, Macedonia [email protected]

An artificial neural network prediction model for fire resistance of centrically loaded composite columns exposed to fire from all sides is presented in this paper. Three different types of composite columns, as: totally encased, partially encased and hollow steel sections filled with concrete, as well as ordinary RC columns were analyzed by using the program FIRE. The effects of the shape, the cross sectional dimensions and the intensity of the axial force were analyzed. The results of the performed analyses were used as input parameters for training the neural network prediction model.Key words: Artificial neural network, Prognostic model, Fire resistance, Composite columns

INTRODUCTION

The legally prescribed time period during which a structure must stay stabile and safe under fire, is actually the time in minutes which represents the fire resistance of a structure. The length of this time period is obligatory in almost every country and it depends on: the height, number of flats, floor area, capacity, content and purpose of the structure, the distance of fire stations and fire brigades, as well as on the fire protection system of the structure [01].

The fire resistance of a structure can be determined based on the estimated fire resistance of whole structure or of each structural element (columns, beams, slabs, walls etc.). The fire resistance of a structural element is the time period (in minutes) from the beginning of the fire until the moment when the element reaches its ultimate capacity (ultimate strength, stability and deformability) or until the ele-ment loses its separation function [01].

Nowadays, as a result of many years of investiga-tions, there are three basic methods for determina-tion the fire resistance of structural elements. The

oldest method is the performance of a fire test of loaded element, the second method implies the use of empirical formulae that are based on the re-sults from performed fire tests and the third method is based on analytical approach and anables not only design of elements but of whole structures with a predefined fire resistance and it is based on the principles of structural mechanics and theory of heat transfer [01].

For the last twenty years, particular importance has been given to analytical definition of the problem, but the need for getting answers to many questions in this field implies the application of new, modern and faster methods for determining the fire resis-tance of structures. The application of neural net-works as such a method for building a prognostic model which can be used for predicting the fire re-sistance for structures and/or their elements is of a huge importance for the design process in con-struction [06], [07].

The goal of the research presented in this paper was to build a prognostic model which could gener-

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ate outputs for the fire resistance of centrically load-ed composite steel-concrete columns for any given input data, by using the numerical results from the existing research program, as input data.

FIRE RESISTANCE OF STEEL-CONCRETE COMPOSITE COLUMNS

The columns, as structural elements, have an im-portant role in preventing loss of global stability of structures under fire. If these elements do not suffer failure, damages shall be of a local charac-ter. The idea for the construction of the composite structures as combination of the two traditional materials, concrete and steel, is based on the ef-fective use of the advantages of both materials. Even before the first composite columns were constructed, the steel columns were encased in concrete to achieve higher fire resistance. This paper presents the numerically achieved results for the fire resistance of centrically loaded steel-concrete composite columns with different cross sections, as: concrete filled hollow steel section CFS, partially encased steel section PES and totally encased section TES (Figure 1). For com-parison a reinforced concrete column (RC) has also been analyzed (as reference one) because it has high fire performance. The columns with fixed-pinned support conditions and exposed to standard fire ISO 834 from all four sides were analyzed by using the computer program FIRE (Fire Response - Cvetkovska 2002). The influ-ence of the shape of the cross section (different types of cross sections), cross sectional dimen-sions (30x30, 30x50, and 40x40) and the inten-sity of the axial force were analysed. The axial load ratio, which is ratio between the applied ax-ial force N and the ultimate force Nu, was varied from 0,1 to 0,5.

Figure 1: Geometry and support conditions, discreti-zation and cross section geometry

NEURAL NETWORK PROGNOSTIC MODEL

The goal of the investigation presented in this paper was to build a prognostic model that could generate outputs for the fire resistance of centri-cally loaded steel concrete composite columns by using the numerical results as input data.

The neural network prediction model was devel-oped by using the software Neural Tools ver.6. The numerical results given in [02] were used as input data and all data were grouped into two separate tables: the data for training and testing the neural network and data for predicting the value of the output variable. During that training process a total of 87 cases were analyzed, 70 (80%) of which belong to the group of cases for training and the rest 17 cases (20%) were used for testing the network. The following four inde-pendent variables were treated as input data: di-mensions of the cross section of the column (a and b), loading coefficient (α) as ration between

the applied axial force and the ultimative axial

force and type of the column (concrete filled hol-

low steel sections CFS, partially encased steel

sections PES, totally encased steel sections

TES and reinforced concrete sections RC, as

reference one). The output was only one vari-

able: the fire resistance of the column expressed

in minutes (t).

Training and testing of the neural networks is an

iterative process that repeats the procedure of

training and testing of several neural networks

with different structure until it generates neural

network which provides the best outcomes [3-

8]. For the multilayered networks with spreading

the information forward (in one direction, from

input to output layer) the learning cycle means

determination of weight coefficients for the con-

nections between neurons, where training is a

smart choice of weight coefficients that get the

best predictions [4-9]. Training stops at the mo-ment when it reaches one of the three conditions defined by the user, namely: the maximum time required for training, the number of training cy-cles, or the change of the error at certain time.

Assessment of prediction accuracy of neural networks is done by comparing the following pa-rameters [10]:

Percentage of bad predictions - denotes the number of cases whose predicted value does not match the expected value, i.e. the predicted value is outside the defined mar-gins for tolerance. It is considered that if this

•

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Marijana Lazarevska-An artificial neural network prediction model for fire resistance of composite columns


value is less than 30% , the accuracy of the network for predicting the output value is sat-isfactory.

Root Mean Square Error that - a measure for the deviation of the predicted from actual values. This is one of the most commonly used measures for differences between the provided values by the model and expected values. These individual differences are still called the prediction errors or residual values and mean Absolute Error (the average de-

•

viation of predicted from actual values).

Nine multilayered neural networks with forward propagation, with one input layer, one hidden layer and one output layer, with different num-ber of neurons in the hidden layer (2 to 10 neu-rons) were trained and tested and the optimal neural network was defined. Training was con-ducted through 1000000 eras or 1000000 cycles of learning. Table 1 shows the results obtained after the testing of all nine neural networks.

Type of neural network % bad predictions RMSE MAE

MLFN with 2 neurons 41.18 1.67 1.27









Table 1. Neural networks testing report

If the percentage of bad predictions is within the allowable limits (less than 30%), then the optimal neural network is the network that has the lowest value of the root mean square error and mean absolute error obtained by testing [10]. Analyzing the results shown in Table 1 it can be concluded that the worst prediction would be obtained if adopted multilayered neural network is with 2 or 10 neurons in the hidden layer. Multilayered

network with 7 neurons in hidden layer gives the lowest error and therefore this structure is ad-opted as the optimal for determination the fire resistance of analyzed columns. The predicted values obtained by trained neural network for the cases used for training and the calculated values for the fire resistance of the columns, expressed in hours, are compared in Figure 2.

Figure 2: Comparison of calculated and predicted values for the fire resistance of composite columns, used for training the neural network

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The predicted values obtained by the trained neural network for the 17 cases that were not used for the training, but for the testing of the

neural network, and the corresponding values calculated with the program FIRE, are compared in Figure 3.

Figure 3: Comparison of calculated and predicted values of the fire resistance of composite RC columns, used for testing the neural network

The histogram of the residual values (average deviation of the predicted value from the calcu-lated value) of the predicted values for the fire resistance of columns for training and testing

data, are presented on Figures 4 and 5. Most of the residual values are around 0 which is a good indicator of the accuracy of the model for predict-ing the fire resistance of this type of columns.

Figure 4: Histogram of the residual values of training data

Graphical presentation of the comparison of the actual (calculated with program FIRE) and the predicted fire resistance values (obtained by the neural network prognostic model) for 27 cases that were not included in the training and testing process, is given on Figure 6.

Based on the results obtained from the numeri-cal analysis and the neural network prognostic model, fire resistance curves were constructed. These curves may be used for determination the

fire resistance of composite steel concrete col-umns that were not previously analyzed. The fire resistance curves for the columns with dimen-sions 30x50 cm and different types of cross sec-tion, constructed by both methods, are present-ed on Figure 7. From these curves, depending on the level of the axial force (load coefficient ) and the type of the cross section, the fire resis-tance of the column could be defined without any additional calculation.

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Figure 5: Histogram of the residual values of testing data

Figure 6: Calculated and predicted fire resistance values for cases that were not included in the training and testing process

Figure 7: Comparison of calculated (actual) and predicted fire resistance curves for centrically loaded compos-ite columns with cross section dimensions 30x50cm

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It can be seen that the corresponding curves con-structed on the basis of the numerically achieved results and on the basis of the results from the neural network approach are similar and give close results.

CONCLUSION

The application of neural networks for prognos-tic modeling which can be used for predicting the fire resistance of structures and/or their el-ements is of huge importance for the construc-tion design process. Most of the experimental models for determination the fire resistance are extremely expensive, and analytical models are quiet complicated and time consuming. That is why a modern type of analyses, such as model-ing through neural networks, can help, especially in those cases where some prior analyses were already made.

The main goal of this research was to explain the simplicity and the positive aspects of the us-age of neural networks for solving engineering problems. After the comparison of both methods it can be concluded that artificial neural networks present an excellent tool for prognostic modeling and can be used for determination the fire re-sistance of steel- concrete composite columns, especially in those cases when there are no (or very few) experimental and/or numerical results.

REFERENCES

Cvetkovska M.: „Nonlinear stress strain behavior of RC elements and plane frame structures exposed to fire“, Ph. D. thesis, Civil Engineering Faculty in Skopje, Sts Cyril and Methodius University, Macedonia, 2002

Cvetkovska M., Milanović M., Jovanoska M., Čifliganec C.: „Parametric analysis of fire resistance of centrically loaded composite steel-concrete columns“, 15th International Symposium of Macedonian Association of Structural Engineers - MASE, Ohrid, Mace-donia, September 2013

Chen A. M., Lu H.-m., Hecht-Nielsen R.: “On the geometry of feedforward neural network error surfaces”, Neural computations, 1993, pp. 910-927

Flood I. and Nabil K.: „Neural networks in civ-il engineering II: Systems and application.“, Journal of Computing in Civil Engineering 8, no. 2, 1994, pp. 149-162

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Flood I. and Paul C.: „Modeling construction processes using artificial neural networks“, Automation in Construction, Volume 4, Issue 4, 1996, pp. 307-320

Flood I.: „Simulating the construction pro-cess using neural networks“, Proceedings of the 7th ISARC – International Association for Automation and Robotics in Construction, Bristol, United Kingdom, 1990, pp. 374-382

Jeng DS, Cha DH and Blumenstein M.: „Ap-plication of Neural Networks in Civil Engi-neering Problems“, Proceedings of the In-ternational Conference on Advances in the Internet, Processing, Systems and Interdis-ciplinary Research (IPSI-2003), 2003

Knežević M.: „Risk management of civil en-gineering projects“, Ph. D. thesis, Civil Engi-neering Faculty, University in Belgrade, Ser-bia, 2005

Knežević M. and Zejak R.: “Neural networks – application for usage of prognostic model of the experimental research for thin rein-forced-concrete columns”, scientific research work, Materials and constructions, 2008.

Lazarevska M., Knezevic M., Cvetkovska M., Trombeva G. A. and Samardzioska T.: „Neural network’s application for predicting the fire resistance of reinforced concrete col-umns“, Journal Gradjevinar. Vol.7, 2012, pp. 565-571

http://www.palisade.com/neuraltools/

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Dr Ivana Štimac Grandić*Faculty of Civil Engineering, University of Rijeka, Rijeka, Croatia

INFLUENCE OF SAMPLING INTERVAL ON DEFLECTION-INFLUENCE-LINE-BASED

DAMAGE DETECTION IN BEAMS

doi:10.5937/jaes12-5668 Paper number: 12(2014)1, 278, 69 -74


In this paper, the influence of sampling interval on reliability of damage detection and damage local-ization based on comparison of deflection influence lines and their derives (slope and curvature) for intact and damaged state is investigated. The numerical analysis is conducted on a simply supported beam with one damaged section for different sampling interval and different position of sampling points to damaged section.Key words: Damage detection, Beam, Deflection influence line, Sampling interval

INTRODUCTION

As it is known, non-destructive techniques for damage detection (existence, localization and estimation of damage) are frequently used in the past few decades. Both, methods established on changes in dynamic, as well as in static responses between two states of structure are developed. Also, some researchers combine these two methods. Static methods were used less than dynamic ones but main advantage of static methods over dynamics that there is no need for dynamic characteristic of structure (mass and damping). Hence, the static methods need less complicated calculation algorithms.

One of the static method is based on compari-son of deflection influence lines or their derives (slope and curvature of deflection influence lines) for non-damaged and damaged structure. This method can be successfully used for dam-age localization [01].

Generally, the influence line graph presents the variation of a function (such as deflection) at a specific point on a structure caused by a unit or any non-unit load load placed at any point along the structure. The position of discrete values of deflection influence line are determined by different load positions where each load position represent one sampling point. It is difficult to expect a large number of sampling points during on-site testing therefore it is necessary to determine the influence of sampling interval to reliability of damage detection and damage localization.

DESCRIPTION OF DAMAGE DETECTION METHOD

In general, structural damage cause changes of the structural response in comparison to the response of non-damaged structure. Structural damage may be defined as any deviation of material or geometric property of the structure (i.e. deviation of structural stiffness).

Let us assume that there is two sets of data collected on structure in different time. By comparing this two sets of data it is possible to get information about changes in response of the structure. If this two data sets are similar, there is no changes in the structural stiffness.

If the structure is damaged, the deflec-tion influence line of non-damaged struc-ture is different form the deflection influence line of damaged structure .

Also, the slope and curvature of deflection influ-ence lines for these two states will be different too. The slope of deflection influence line for non-damaged and damaged structure is presented by equations (1a and 1b), and the curvature of deflection influence line for non-damaged and damaged structure is presented by equations (2a and 2b):

(1a), (1b)

(2a), (2b)

69* Faculty of Civil Engineering, Viktora Cara Emina 5, 51 000 Rijeka, Croatia [email protected]


Subtracting the deflection influence lines or their slope or curvature gives the information about damage:

the maximum difference in the deflection influence lines point at the location of the damage [02-06];

the location of the dam-age is represented by vertical jump in the difference in the slope of the deflection influence lines [02-05];

the location of the damage is represented vertical peak in the difference in the curvature of the deflection influence lines [02-05, 07].

NUMERICAL ANALYSIS

The analysis has been carried out for simply supported beam. The span length of the beam is L=25 m. The cross section area of the beam is A=0.8567m2, the moment of inertia is I=0.14 m4

and Young’s modulus is E=3.5∙107 kN/m2. The

applied force is F=100 kN. The numerical mod-

el has 100 beam finite elements and 101 finite

element nodes (numbered from 0 to 100). The

length of each finite element is x=0,25 m.

I.

II.

III.

The displacement influence lines have been

computed for point in the middle of the span for

both the non-damaged and the damaged beam.

The damage has been simulated by reducing

the bending stiffness of 29th and 30th finite ele-

ments by 20%. The damage is situated between

7 and 7,5 m from left support (Figure 1).

The slope and the curvature of the displacement

influence lines have been calculated using finite

difference method according to equations (3a.

3b 4a and 4b):

(3a), (3b)

(4a), (4b)

The four sets of deflection influence lines for non-

damaged and damaged beam were calculated.

In the first set the sampling interval is ds=0,25 m;

in the second set is ds=0,75 m; in the third set is

ds=1,25; in the fourth is ds=2,5 m.

On Figures 2-4, there are shown the differences

in the deflection influence lines, the differences

in the slope of the deflection influence lines and

the differences in the curvature of the deflection

influence lines for different sampling intervals

ds. As it can be seen, the damage detection is

successful regardless of sampling interval. The

differences in the deflection influence lines in all

analysed cases point at the position of 7,5 m as

potential point of damage (Figure 2). A potential

damage section can be estimated by using the

difference in the slope/curvature of the deflec-

tion influence lines; in cases where simulated

damaged section is narrower than the sampling

interval (Figures 3 and 4) the detected damaged

section is wider than it is simulated.

Figure 1: Position of the damaged section

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Dr Ivana Štimac Grandić-Influence of sampling interval on deflection-influence-line-based damage detection in beams

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Figure 2: The difference in the deflection influence lines for different sampling interval ds

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Figure 3: The difference in the slope of the deflection influence lines for different sampling interval ds

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Figure 4: The difference in the curvature of the deflection influence lines for different sampling interval d

s

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CONCLUSION

In the paper, the influence of sampling inter-val on deflection influence line based damage detection method in beams is investigated. Conducted numerical analysis shows applicabil-ity of this method even when small number of sampling point is used.

On-site testing can be carried out using rela-tively small number of sampling point to detect and roughly locate the damage. Afterwards, the potential damaged location can be tested again with smaller sampling interval or by using other non-destructive technique (such as ultra-sound) to determine the damage location more accurately.

REFERENCES

I. Štimac: „Uporaba utjecajnih linija progiba u otkrivanju oštećenja konstrukcija“, Dis-ertacija, Građevinsko-arhitektonski fakultet

Sveučilišta u Splitu, Split, 2006, 139 str.

I. Štimac, A. Mihanović, I. Kožar: „Upor-aba utjecajnih linija progiba za otkrivanje oštećenja na grednim konstrukcijama“, Prvi sabor hrvatskih mostograditelja, Brijunski otoci, 2005, str. 747-754

I. Štimac, A. Mihanović, I. Kožar: „Damage Detection from Analysis of Displacement In-fluence Lines“, International Conference on Bridges, Dubrovnik, 2006, str. 1001-1008

I. Štimac, I. Kožar: „Damage Detection from Displacement-in-time Function“, 4th Youth Symposium on Experimental Solid Mechan-ics, Bologna, 2005, pp. 3-4

I. Štimac Grandić, D. Grandić, A. Bjelanović: „Comparison of Techniques for Damage Identification Based on Influence Line Ap-proach“, Machines, Technologies, Materials, 7, 2011, pp. 9-13

I. Choi, et al.: “Development of elastic dam-age load theorem for damage detection in statically determinate beam”, Computer and Structures, 82(29-30), 2004, pp. 2483-2492,.

I. Štimac, I. Kožar, A. Mihanović: „Otkrivanje oštećenja greda s pomoću utjecajnih linija pro-giba“ Građevinar, 59(12), 2007, str. 1053-1066

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75

Dr Marko Pavlović*Faculty of Civil Engineering, University of Belgrade, Belgrade, Serbia

Dr Milan SpremićFaculty of Civil Engineering, University of Belgrade, Belgrade, Serbia

Dr Zlatko MarkovićFaculty of Civil Engineering, University of Belgrade, Belgrade, Serbia

Dr Dragan BuđevacFaculty of Civil Engineering, University of Belgrade, Belgrade, Serbia

Dr Milan VeljkovićLuleå University of Technology, Sweden

RECENT RESEARCH OF SHEAR CONNECTION IN PREFABRICATED STEEL-CONCRETE

COMPOSITE BEAMS



Prefabrication of steel-concrete composite decks can improve their competitiveness and sustainabil-ity. This paper presents recent studies of longitudinal shear connection at the University of Belgrade, Faculty of Civil Engineering. Grouped welded headed studs and bolted shear connectors, suitable for prefabricated composite construction, has been examined in push-out tests. Totally 30 tests were conducted, and advanced FEA were made using Abaqus/Explicit dynamic solver. Based on the ex-perimental and numerical studies behaviour those two shear connectors are compared.

Key words: Prefabricated composite beams, Grouped headed studs, Bolted shear connectors

INTRODUCTION

Steel-concrete composite beams have been used in buildings and bridges for decades. In-situ casted concrete often requires temporary supports and formwork. Prefabrication of con-crete slabs is a good way to reduce the construc-tion time and optimize the construction process. Composite action between a steel profile and a concrete slab is most commonly established by grouting grouped headed studs welded to the top flange of the steel section in envisaged openings

(pockets) in prefabricated concrete slabs (see Figure 1). A possible alternative solution is to use high-strength bolts to establish longitudinal shear connection. Bolts can be casted in pre-fabricated concrete slabs (see Figure 2) and on site assembled to the predrilled top flange of the steel section part of composite member. This so-lution offers great prefabrication benefits, since no time is needed for grout hardening. Usage of bolted shear connectors also improves the sustainability of construction as the structure will have to be removed at the end of its lifetime.

Figure 1: Prefabricated concrete slabs with openings for grouped shear connectors

* Faculty of Civil Engineering, Bulevar kralja Aleksandra 73, 11 000 Belgrade, Serbia [email protected]


Figure 2: Possible application of bolted shear connectors embedded in prefabricated concrete slabs

Apart from evident benefits arising from application of the mentioned solutions, there are still no specific design rules in design codes, which is an obstacle for their wide application. Possible reason could be the lack of detailed research of specific behaviour of such shear connections. For example, EN1994-2 [01] (Eu-rocode 4 for bridges) allows usage of headed studs in grouped arrangement, but only some general recommendations are given. According to [01] following facts need to be considered: the non-uniform flow of longitudinal shear, the great-er possibility of slip and vertical separation be-tween the slab and the steel member, buckling of the steel flange and the local resistance of the slab to the concentrated force from the connec-tors. Additionally, it is given that in the case of grouped arrangement the longitudinal spacing of groups may be greater than the maximum al-lowed spacing for individual shear connectors, but the limits are not given.

The principle of usage of grouped headed studs can be explained as shown in Figure 3 by re-placing the block shear connector with group of headed studs. Research on grouped arrange-ment of welded headed studs, in last two de-cades, is pointed towards the reduction of lon-gitudinal spacing between the studs within the group. This would allow smaller openings that are needed to accommodate the groups of studs in prefabricated concrete slabs and therefore more compact concrete slab with less disconti-nuities. Previous studies, conducted by Okada et al. [02] and Shim et al. [03], investigated the shear capacity of nine large headed studs (22 mm and 25 mm) arranged in groups with reduced

longitudinal spacing between studs. These stud-ies were intended for studying grouped studs application in precast composite bridge struc-ture. These authors suggested the reduction co-efficient for individual shear resistance of studs when arranged in groups. Suggested coefficients are in function of longitudinal spacing between the studs.

Figure 3: The principle of replacing the block shear connector with grouped headed studs

Possible uses of bolted shear connectors are shown in Figure 4. The composite action can be established with or without nuts embedded in the slab, either with or without preloading of the bolts. They have been investigated by several previous studies: Marshall et al. [04], Dedic and Klaiber [05], Hawkins [06], Sedlacek et al. [07], ,Kwon [08], Lee and Bradford [09]. Except for the friction grip bolts, shown in Figure 4a, none of the mentioned studies gave the detailed expla-nation of behaviour of such shear connectors, and the design rules in worldwide design codes are still not present.

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Dr Marko Pavlović-Recent research of shear connection in prefabricated steel-concrete composite beams

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The research program considering solutions for longitudinal shear connection in prefabri-cated composite construction is being realised on University of Belgrade – Faculty of Civil Engineering in recent years, through PhD the-ses of Spremić [10] and Pavlović [11]. Experi-mental and numerical studies was conduct-ed with the aim to analyse possibilities to use grouped headed studs in prefabricated compos-ite beams in buildings. The group of four studs with 16,0 mm diameter has been investigated.Basic shear connector’s properties have been

investigated throughout the study such as: shear resistance, stiffness and ductility, as well as the possibility to reduce the spacing between adja-cent headed studs in the group. Bolted shear connectors with single embedded nut, shown in Figure 4c, were considered because they have much higher shear stiffness when compared to other types. In addition, they are more suitable for casting in prefabricated concrete slabs since they can be mounted by the nuts on both sides to a template in the formwork.

Figure 4: Different types of bolted shear connectors

EXPERIMENTAL WORKS

Experimental works included 30 standard push-out tests: 24 test with grouped studs and 8 test with bolted shear connectors. The materials, initial assumptions and test set up were in ac-cordance with EN1994-1-1 [12]. The layout of specimens is shown in Figure 5.

The study considered five different groups of four headed studs, with the distance between headed studs less than the minimum distances required in EC4 [1] and [12]. The layout of group arrangement along with its orientation to the ap-plied load and distance between the studs were the variables that were considered (see Figure 6a). The aim was to determine how does the reduction of the minimum required spacing be-tween the headed studs affects the behaviour of the shear connection: shear resistance, ductility and total longitudinal shear deformation. Anal-ysed groups were formed with longitudinal spac-

ing between the studs s = 45 mm (2.8d) to s = 50 mm (3.1d). The push-out specimens GR1, G1 were constructed with deferent types of pre-cast concrete slabs. The concrete slabs without reinforcement bars in front of the studs groups were used for the push-out specimens G1. Bolts grade 8.8, with diameters M16 and M24, were examined experimentally (see Figure 6b), while other diameters were considered through a para-metric FEA study.

Specimens were assembled in two phases, one side than another, by concreting openings in hor-izontal position (see Figure 7a). Upon 28 days after specimen preparation, they were equipped with sensors mounts, and put into testing frame with hydraulic jack. Each specimen was equipped with 8 LVDTs (Linear Variable Displacement Transducer), as shown in Figure 7b in order to measure the longitudinal slip and separation between steel flange and the concrete slabs.

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a) grouped headed studs

Figure 5: Push-out tests layout

b) bolted shear connectors

Figure 6: Different arrangements of grouped headed studs and diameters of bolted shear connectors analysed in the study

The force was measured by a load cell at the top, with capacity of 1000 kN.

Results of push-out tests are presented in Fig-ure 8 as averaged force-slip curves (within the 4 specimens) for different types of shear con-nection examined. All results of push-out tests with headed studs group have the ultimate shear resistance greater then characteristic shear re-sistance according to EC 4 [01] and [12]. The values of ultimate shear resistance of the group arrangements G1 and GR1, LDA2, with two headed studs in the direction of the load at a smaller distance than recommended 5d are the same or higher than the ultimate bearing resis-

tance of standard ST type specimens. Average values of ultimate failure load for the G1 type specimens and GR1 type specimens demon-strate that transversal reinforcement in the slab does not have considerable influence on the shear resistance. Bolted shear connectors M16 showed similar shear resistance as the compara-ble headed studs, while bolts M24 reached much higher shear resistance, with ductile behaviour. Two types of failure modes were recognized for bolted shear connectors: shear failure of the connector and pryout failure of the concrete in front of the shear connector.

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a) half assembled specimens b) measurements layout

Figure 7: Assembling of the specimens and testing in the hyraulic jack

Figure 8: Averaged force-slip curves for different arangements of grouped headed studs and diameters

of boltes shear connectors

NUMERICAL FEA STUDIES

Extensive advanced finite element analyses (FEA) were conducted alongside the experimen-tal works as illustrated in Figure 9. Firstly, the verification FEA was made in order to calibrate the models by matching the results to push-out test. ABAQUS/Explicit solver with damage mate-rial models were used to get more insight into behaviour of the specimens and failure modes. Afterwards, those models were used for para-metric studies with aim to develop design recom-mendations. Some of the results have already been published in [13] and [14].

CONCLUSION

Based on the results of presented study it is con-cluded that prefabrication of steel-concrete com-posite beams by use either of grouped headed studs or bolted shear connectors is feasible. This study went beyond the state-of-the-art giv-ing the practical design recommendations for those types of shear connection. A concept of equivalent diameter of group of headed studs is introduced in [13] and a reduction factor for shear resistance of headed studs in groups is derived as its function. Complete calculation models for shear resistance and ductility of bolted shear connectors were developed in [14] based on two possible failure modes (bolt and concrete). Moreover, pryout failure of the con-crete has been explained analytically for the first time. Design recommendations, both in cases of grouped headed studs and bolted shear connec-tors, are proposed in a form which is suitable for adoption in EC4.

ACKNOWLEDGEMENTS

The study presented in this paper is supported by the Serbian Ministry of Education, Science and Technological Development through the TR-36048 project. Support provided by “MB steel” Ltd. and “GEMAX” Concrete production Ltd. from Bel-grade was beneficial for specimen production.

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b) Bolted shear connectors

REFERENCES

Dedic DJ, Klaiber WF. High-Strength Bolts as Shear Connectors in Rehabilitation Work. Con-crete international 1984;6(7):41–46.

EN1994-1-1: Eurocode 4 - Design of composite steel and concrete structures. Part 1-1: General rules and rules for buildings. Brussels, Belgium: European Committee for Standardization (CEN); 2004.

EN1994-2: Eurocode 4 - Design of Composite Steel and Concrete Structures. General Rules and Rules for Bridges. Brussels, Belgium: European Committee for Standardization (CEN); 2005.

Hawkins N. Strength in shear and tension of cast-in-place anchor bolts. Anchorage to Concrete 1987;SP-103:233–255.

Kwon G. Strengthening existing steel bridge gird-ers by the use of post-installed shear connectors. PhD thesis. The University of Texas at Austin, 2008:p.239.

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Figure 9: Finite element analyses of tested speci-mens and parametric studies

Lee M. Bradford MA. Sustainable composite beam behaviour with deconstructable bolted shear con-nectors. Proceedings of the 2013 Composite Con-struction in Steel and Concrete VII.

Marshall WT, Nelson HM, Banarjee HK. An ex-perimental study of the use of high strength fric-tion-grip bolts as shear connectors in composite beams. The Structural Engineer 1971;49(4):171-178.

Okada J, Teruhiko Y, Lebet JP., A study of the grouped arrangements of stud connectors on shear strength behaviour, Structural Eng./Earth-quake Eng.,JSCE 2006;23(1):75-89.

Pavlović M, Marković Z, Veljković M, Budjevac D, Bolted shear connectors vs. headed studs behav-iour in push-out tests, Journal of Constructional Steel Research 2013;88:134-149.

Pavlović M., Resistance of bolted shear connec-tors in prefabricated steel-concrete composite decks, PhD thesis, University of Belgrade, Faculty of Civil Engineering; 2013.

Sedlacek G. Hoffmeister B. Trumpf H. Kühn B. et al. Composite bridge design for small and medium spans. Final report. European Commis-sion – technical steel research Contract No 7210-PR/0113. Luxembourg, 2003.

Shim CS, Lee, PG, Kim DW, Chung CH., Effects of Group Arrangement on the Ultimate Strength of Stud Shear Connection. Proceedings of the 2008 Composite Construction in Steel and Concrete Conference VI, ASCE Conf. Proc.

Spremić M, Marković Z, Veljković M, Budjevac D., Push–out experiments of headed shear studs in group arrangements, Advanced Steel Construc-tion; 2013,9(2):170–191.

Spremić M., The analysis of headed studs group behavior in composite steel-concrete beam, PhD thesis, University of Belgrade, Faculty of Civil En-gineering; 2013.

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Dr Cristina Campian*Technical University of Cluj, Belgrade, Cluj-Napoca, Romania

Alina Haupt-KarpTechnical University of Cluj, Belgrade, Cluj-Napoca, Romania

Maria PopTechnical University of Cluj, Belgrade, Cluj-Napoca, Romania

Dr Nicolae ChiraTechnical University of Cluj, Belgrade, Cluj-Napoca, Romania

Gabriel UrianTechnical University of Cluj, Belgrade, Cluj-Napoca, Romania

Dr Paul PernesTechnical University of Cluj, Belgrade, Cluj-Napoca, Romania

BEHAVIOR OF FULLY ENCASED STEEL-CONCRETE COMPOSITE COLUMNS

SUBJECTED TO MONOTONIC AND CYCLIC LOADING



The paper presents a numerical model developed for fully encased steel-concrete composite columns under monotonic and cyclic loading. The numerical model was realized with the FineLg program, developed at ArGenCo department, University of Liège. The numerical model was validated using five experimental tests taken from the international literature: two realised at Technical University of Cluj-Napoca and the others in Taiwan, USA and China. The experimental tests used for validation of the numerical model dealt with both normal and high strength concrete. Different parameters were compared in the paper: partial and full ductility, energy dissipation, resistance and rigidity ratio.Key words: Fully encased composite columns, Numerical model

81* Technical University of Cluj-Napoca,Str.ConstantinDaicoviciunr.15, 400020 Cluj-Napoca, Romania [email protected]

INTRODUCTION

Aside the experimental research on fully encased steel-concrete composite columns, another very important side is the analytical research, the mathematical modeling of the member behavior, under monotonic and cyclic loading. Computer simulation of the behavior of elements is a much cheaper, rapid and efficient method of research, but it cannot exclude and reduce the importance of experimental research. The calibration of proposed numerical model was based on five experimental programs taken from the interna-tional literature.

EXPERIMENTAL PROGRAMS USED FOR VALIDATION OF THE NUMERICAL MODEL

The first two experimental programs used for val-idation were developed in the Structures Depart-ment, at Faculty of Civil Engineering, Technical University of Cluj-Napoca, Romania, year 2000

and 2011.The third program was developed at National Central University in Taiwan, year 2008. The forth experimental research was developed at California University in San Diego, USA in 1992 and the fifth at Chiao Tung University, Hsinchu, China, in 2008. The first four experimental pro-grams used I type steel profiles and the last used cross steel profiles fully embedded in concrete. All columns were subjected to compressive axial loading and bending moment (induced by hori-zontal lateral forces), except the fourth program where the columns were additionally subjected to shear too. The mechanical model and test up procedure for all experimental programs are pre-sented in Figure 1.

EXPERIMENTAL PROGRAM DEVELOPED AT UTC-N, ROMANIA, 2000

The experimental program realized by Cristina Campian, 2000, at Technical University of Cluj-Napoca, Romania, included 12 tests (3 mono-


tonic and 9 cyclic) on fully encased steel-con-crete composite columns. All columns had the same cross-section and were grouped accord-ing to their length. The elements were made with a Romanian steel section I12 (which is quasi

similar to IPE 120 section) fully covered with re-inforced concrete including 4 ф 10 longitudinal bars as shown in Figure 2. In Table 1 are pre-sented some characteristics of the tested speci-mens.

Figure 1: Mechanical model and test up procedure for experimentally tested columns

Figure 2: Cross-section of the tested specimens and failure mode

Table 1: Characteristics of tested specimens

Column

type

Length

[m]

Compressive

concrete strength

[N/mm2]

Concrete

Young

modulus

[N/mm2]

Yield strength

of longitudinal

reinforcement

[N/mm2]

Longitudinal

reinforcement

Young modulus

[N/mm2]

Yield

strength of

embedded

profile

[N/mm2]

Embedded

profile Young

modulus

[N/mm]

SI 2.00 30.5 -

SII 2.50 27.0 - 559 207000 302 207000

SIII 3.00 29.5 37373.33

The failure of all tested columns was governed by the plastic hinge formation at column base (see Figure 2)

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Dr Cristina Campian-Behavior of fully encased steel-concrete composite columns subjected to monotonic and cyclic loading



The two types of composite columns tested by Vlăduț Sav, 2011, were similar to the ones tested at Technical University of Cluj-Napoca in 2000. The main difference between the experimental programs was the type of concrete used. The author of the experimental program use high

strength concrete, class C70/85. The tested col-umns had 2 different lengths: 3.00 m (columns S1, S2, S3 and S4) and 2.00 m (columns S5, S6, S7 and S8). The cross-section of the composite column was the same for all tested specimens, of 170x220 mm (see figure 3), with an IPN120 embedded profile and 4 Ø10 bars as longitudinal reinforcement.


The two types of composite columns tested by Vlăduț Sav, 2011, were similar to the ones tested at Technical University of Cluj-Napoca in 2000. The main difference between the experimental programs was the type of concrete used. The author of the experimental program use high

strength concrete, class C70/85. The tested col-umns had 2 different lengths: 3.00 m (columns S1, S2, S3 and S4) and 2.00 m (columns S5, S6, S7 and S8). The cross-section of the composite column was the same for all tested specimens, of 170x220 mm (see figure 3), with an IPN120 embedded profile and 4 Ø10 bars as longitudinal reinforcement.


In Table 2 are presented a few characteristics of the tested specimens. The author performed first

monotonic tests on both type of columns and af-ter, three cyclic tests for each type of column.

Table 2. Characteristics of tested specimens

Compressive concrete strength

[N/mm2]

Concrete Young modulus

[N/mm2]

Yield strength of steel

[N/mm2]

92,3 43634,65 380.20

The failure mode was similar for all tested speci-mens. In comparison with the columns made with normal concrete and presented at 2.1, the failure of the columns made with high strength concrete was violent and brittle.

EXPERIMENTAL PROGRAM DEVELOPED AT NCU, CHUNG-LI, TAIWAN, 2008

The experimental study made by H. L. Hsu, F. J. Jan and J. L. Juang, 2008, was developed at the Department of Civil Engineering, National Central University, Chung-Li, Taiwan. All tested columns had the same cross-section, 370 mm x 370 mm (see Figure 4), with six different embed-

ded profiles (Table 3). The type of loading and direction are presented also in Table 3.

Identical reinforcement were used in all speci-mens, 4Φ20 as longitudinal reinforcement and Φ 9.525 stirrups. The stirrup spacing was 100 mm within the confined zones and 150 mm in the non-confined zones. Yield strength for the struc-tural steel, longitudinal bars and stirrups were 314 MPa, 543 MPa and 586 MPa respectively. The concrete compressive strength, determined from cylinder tests was 38 MPa.

The member performances were governed by plastic hinge formation, as shown in Figure 4.


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Column type Embedded profile Loading direction Loading type

YAM H100x100x6x8

YBM H150x100x6x9

YDM H200x100x5.5x8

YCM H150x150x7x10

YEM H200x150x6x9

YFM H200x200x8x12 Weak-axis bending monotonic

XAC00 H100x100x6x8

XBC00 H150x100x6x9

XDC00 H200x100x5.5x8

XCC00 H150x150x7x10

XEC00 H200x150x6x9 Axial loading + strong-axis bendingXFC00 H200x200x8x12 cyclic


EXPERIMENTAL PROGRAM DEVELOPED AT UC, SAN DIEGO, CALIFORNIA, SUA, 1992

The experimental program realized by James M. Ricles and Shannon Paboojian, 1992, was performed on fully encased steel-concrete com-posite columns, subjected to compressive axial load, bending moment and shear. The tests were

developed at California University in San Diego, USA. The composite columns analyzed consisted of a W8x40 steel profile encased in a 406x406 mm reinforced concrete section. The two cho-sen sections used for validation of the numerical model had the same length, the same embedded profile and the same longitudinal and transversal reinforcement, but different concrete class.


Specimen no.

db [mm]s

[mm]Length [mm]

Concrete compressive

strength[N/mm2]

Yield strengthsteel profile

[N/mm2]

Yield strengthreinforcement

[N/mm2]

3 22.2 95.3 1930 30.9 373 479.2

7 22.2 95.3 1930 62.9


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Specimen 3 was made with normal concrete and specimen 7 with high strength con-cre¬te (the com-pressive resistance is larger than 60 MPa). The cross-section of the tested co-lumns is presented in figure 5 and some characteristics regarding the specimens in Table 4.

The authors of the experimental tests performed only cyclic tests on the studied specimens. The fail-ure of the tested specimens was similar to the other experimental studies presented (see Figure 5).

EXPERIMENTAL PROGRAM DEVELOPED AT CTU, HSINCHU, CHINA, 2008

The experimental program developed by Weng ChengChiang, Yin YenLiang, Wang JuiChen and Liang ChingYu, 2008, aimed the use of a multi-

spiral cage of five interconnected spirals, named “5-spirals” as transversal reinforcement for rect-angular columns. The tests were performed at the Department of Civil Engineering from Chiao Tung University, Hsinchu, China. All tested col-umns had the same cross-section, of 600 mm x 600 mm and the same height of 3250 mm. The columns had a cross steel profile 2H350x175x6x9 fully embedded in concrete (see Figure 6). The longitudinal reinforcement was the same, 16 Ø 25+4 Ø 13. The diameter of the perimetral spiral was Ø 13 and for the four corner spirals Ø 10. The distances between the spirals were differ-ent, 95 mm for C-SRC1 column and 115 mm for the C-SRC2 column. The resistance of the ma-terials were determined experimentally and are presented in Table 5.



Concrete compressive strength[N/mm2]

Yield strength steel profile[N/mm2]

Yield strength reinforcement[N/mm2]

37.3 435.3 437

The tests ended when the drift angle of the com-posite column reached 6.0% radians. The con-crete cover near the column base was tangibly flaked off, but the concrete confined by the 5-spirals remain intact, the longitudinal reinforce-ment did not buckle, nor did the spirals break, as shown in figure 6.

NUMERICAL MODEL FOR STEEL-CONCRETE COMPOSITE COLUMNS

Calibration and material laws

The numerical model was developed in FineLg, a finite element program developed at ArGen-Co department, University of Liège, Belgium. The proposed numerical model was calibrated

against the five test results presented previ-ously. The columns were considered as plane bars with 3 nodes (see figure 7). Node 1 and 3 has three degrees of freedom (m, u, q). Node 2 has only one degree of freedom, which permits taken into account an eventual displacement be-tween steel and concrete. In the analysis is con-sidered a perfect connection between steel and concrete. The model uses multi-fibers beam ele-ments with mono-axial nonlinear material laws for concrete, embedded steel and reinforcement steel (see figure 9). Because the validation of the numerical model was performed using experi-mental data, for the resistance of materials the safety coefficients were considered equal to 1.

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The steel elements (embedded profile and lon-gitudinal reinforcement) are defined using a bi-linear law, presented in Figure 8a. The local and general bucking effects are not considered in the model. The buckling of the longitudinal reinforce-ment is prevented by the transversal confining

reinforcement. A parabolic-rectangle law is used for concrete in compression (see figure 8c). The law takes into account the tension resistance of the concrete, which is evaluated with the SR EN 1992-1-1 formula.

Figure 7: Finite element

Figure 8: Material laws used in calibration

Figure 9: Calibration of monotonically and cyclically tested column

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The creep and shrinkage effects were not taken into consideration. In the model were used the confined values of the concrete. For normal con-crete was used the SR EN 1992-1-1 law and for high strength concrete the Cusson-Paultre law. For simplicity the section was considered divid-ed into two zones, confined (the zone between the transversal reinforcement) and unconfined (at the exterior of the transversal reinforcement). For the cyclic loading the Menegotto-Pinto law was used (see Figure 8b).

VALIDATION OF THE NUMERICAL MODEL

The validation of the numerical model is pre-sented in figure 10, by comparing the force-dis-placement curves obtained experimentally and numerically. Figures 10a and 10b present the results for the SIII column from the program pre-sented at 2.1., tested monotonically and cycli-cally. Figures 10c and 10d present the results

for the 2.00 m column made with high strength concrete from the Cluj-Napoca experimental program. Figures 10e and 10f present the com-parison for YDM monotonically tested column and for XFC00 cyclically tested column from the experimental program developed in Taiwan. The experimental program developed in San Diego included only cyclic tests on columns made with both normal (see figure 10g for specimen 3) and high strength concrete (see figure 10h for speci-men 7). The validation of the numerical model for columns with cross profiles fully embedded in concrete is presented in figures 10i and 10j. Un-til reaching the peak load the numerical model is quite accurate, the differences between the experimental and numerical values being under 5%. After the peak load the numerical model doesn’t offer such accurate results as before, the differences being about 15%.

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Figure 10: Validation of the numerical model

CONCLUSION

The solution of fully encased composite column is a competitive solution for seismic and non-seismic zones, due to the excellent seismic per-formances (resulted from the presented experi-mental tests) and also because of improved fire protection. The numerical modeling is a very effi-cient and economic investigation method for the behavior of fully encased steel-concrete com-posite columns, especially for sections that are not covered by the current provisions of the SR EN 1994-1-1, but cannot exclude experimental research. The results obtained on the columns made with high strength concrete showed im-proved performances, especially resistance. Due to the brittle fracture of the high strength concrete more experimental and numerical re-search must still be made.

REFERENCES

ASRO. SR EN 1992-1-1, Eurocod 2: Proiect-area structurilor de beton; Partea 1-1: Reguli generale și reguli pentru clădiri, Iunie, 2006. Bucuresti: Asociaţia de standardizare din Romȃnia (in Romanian).

ASRO. SR EN 1994-1-1, Eurocod 4: Proiec-tarea structurilor compozite de oțel și beton; Partea 1-1: Reguli generale și reguli pentru clădiri, Mai, 2006. Bucuresti: Asociaţia de

1)

2)

standardizare din Romȃnia (in Romanian).

Câmpian Cristina. Contribution a l’etude du comportament et au calcul de poteaux mixtes acier-beton (sous des charges transversales de variation monotone ou cyclique alternee), Teză de doctorat, INSA Rennes, 2001.

Cusson D., Paultre P. Prediction of effective confinement pressure in high-strength con-crete columns, CSCE 2008 Annual Confer-ence Structural Specialty, Quebec City, QC., June 10-13 2008, pp. 10.

ECCS (1986): Recommended testing pro-cedure for assessing the behaviour of struc-tural steel elements under cyclic loads, Doc. no 45 of European Convention for Construc-tional Steelwork, TWG 1.3, 1986.

FineLg User’s manual, V9.0 (2004) – Uni-versity of Liège (M&S)/Design office Greisch (BEG)

Hsu H-L, Jan F., Juang J-L. Performance of composite members subjected to axial an bi-axial bending, Journal of Constructional Re-search 65, 869-878, 2009.

Sav Vlăduț. Stâlpi cu secțiune mixtă oțel-be-ton folosind beton de înaltă rezistență, Teză de doctorat, Cluj Napoca, 2011.

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POSSIBILITIES OF USE OF PRODUCTS FROM WASTE TYRE RECYCLING IN

CONCRETE INDUSTRY Dr Marijana Serdar*Faculty of Civil Engineering, University of Zagreb , Zagreb, Croatia

Ana BaričevićFaculty of Civil Engineering, University of Zagreb , Zagreb, Croatia

Dr Dubravka BjegovićFaculty of Civil Engineering, University of Zagreb , Zagreb, Croatia

Dr Stjepan LakušićFaculty of Civil Engineering, University of Zagreb , Zagreb, Croatia

89

Paper presents the effect of products obtained during recycling of waste tyres on properties of con-crete. Only by taking into account specific properties of each product obtained by recycling, it is pos-sible to apply them in concrete industry for preparation of concrete products with special properties. Products incorporating waste tyres can then be ecologically, technically and economically competi-tive alternative to products traditionally used in engineering practice.Key words: Waste tyres, Recycled rubber, Recycled steel fibres, Recycled textile fibres

* Faculty of Civil Engineering, University of Zagreb, Kačićeva 26, 10000 Zagreb, Croatia

[email protected]

INTRODUCTION

Extensive use of tyres in car industry has result-ed in accumulation of large quantities of used tyres that have to be disposed of at the end of their useful life. As many as 1.5 billon of tyres for the automobile industry are produced worldwide each year, and almost 3.5 million tons of waste tyres are generated in the EU countries alone [01]. According to the Directive 1999/31/EC [02], any form of disposal of used tyres in natural en-vironment has been completely banned since 2006 and, following this decision, the quantity of available used tyres has grown considerably. Recent data show that the quantity of waste

tyres disposed in an uncontrolled manner has reduced considerably in Europe over the past decade, and that it now amounts to no more than 4% of the total quantity of waste tyres. At the same time, it is estimated that 29% of waste tyres (about 450,000 t or about 42.5 millions of tyres) are disposed of in an uncontrolled man-ner in new EU member countries. Tyre recycling belongs to the field of sustainable development as the recycling of used products results in valu-able raw materials that can be used for manu-facturing products with a new value. Three raw materials can be obtained by waste tyre recy-cling: a) rubber granules, b) steel fibres, and c) textile fibres (Figure 1).

Figure 1: Products obtained by the automobile tyre recycling: a) rubber granules, b) steel fibres, and c) textile fibres [03]


Only 5% of recycled waste tyres are currently used in construction industry, although the pos-sibilities for such use are much greater in this field. In recent times, rubber has found its use in cement industry, in the production of surfaces for playfields and sports terrains, and as a com-ponent of various lining and covering products. In addition, one of new directions that has been studied over the past several years is the use of waste tyres and their components in the concrete manufacturing technology, since concrete tech-nology is trying to reduce environmental impact of production, and at the same time contribute to the preservation of natural resources [04].

USE OF RUBBER GRANULATES

One of advantages of the use of rubber as a re-placement for some of the aggregate is the re-duction in the density of concrete mix. Further-more, the nonpolarity of rubber, and roughness of its surface, result in introduction of an addi-tional quantity of air [03, 05]. The addition of rub-ber to the fresh concrete mixture also results in a reduced workability, especially when greater pro-

portions are added (>30% of the total volume of aggregate) [05]. The replacement of aggregate with rubber reduces the compressive strength and stiffness in the composite, which could have been expected considering the physical and me-chanical properties of rubber compared to stone aggregate. The capability of rubber to reject wa-ter, due to hydrophobicity of its surface, and con-sequent introduction of an additional quantity of air into the mixture, ensures a greater quantity of closed pores in the composite structure that are not available to water [06]. This is why these composites have a lower capability to absorb water by capillary absorption. Despite a lower capillary absorption, the presence of rubber par-ticles causes higher penetration of water under pressure, due to the poor quality of the rubber to cement matrix interface, but also to physical properties of rubber which “shrinks” when sub-jected to high water pressure [07]. Furthermore, physical properties of rubber enable this material to behave as an absorber of internal stress due to hydrostatic pressure of water during the freez-ing and thawing cycle [05, 08].

Figure 3: Influence of aggregate replacement with recycled rubber on hardened concrete

Figure 4: Structure of concrete without rubber (a) and 10% of rubber (b) after exposure to freezing and thawing cycles with deicing salt

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Dr Marijana Serdar-Possibilities of use of products from waste recycling in concrete industry


Presented main influences of incorporating rub-ber in concrete mixture make the recycled tyre attractive for use in construction industry, where compressive strength is not prevailing factor, but durability in aggressive environments. It is precisely because of these properties that new trends in the use of rubber in concrete are ori-ented toward development of products in which good use can be made of its insulating and ab-sorbing properties [03, 09], its capacity to absorb energy in high-strength concrete [10], and as a replacement for chemical admixtures that are used for increasing resistance to freezing and thawing [05].

USE OF RECYCLED STEEL FIBRES

Studies conducted so far to define possibilities for the use of steel fibres from waste tyres have

revealed several positive features of this mate-rial [03, 10, 11]. In fact, recycled fibres are an economically and environmentally justified alter-native to industrial fibres, especially when used in greater proportions and if mixed with industrial fibres [12]. They limit propagation of cracks and increase toughness of the composite compared to ordinary concrete, even in case of separation and pulling out of the composite [13]. A com-parison of fibre reinforced concrete containing industrial fibres, with fibre reinforced concrete containing the same and higher quantity of re-cycled fibres obtained by automobile tyre recy-cling, is presented in form of diagram in Figure 5. This diagram shows that the design of mixes with recycled fibres results in properties that are similar to those of mixes prepared with industrial fibres.

Figure 5: Working diagram of fibre reinforced concretes containing different types and quantities of steel fibres during ductility testing

In addition to its influence on ductility, the intro-duction of steel fibres in fibre reinforced concrete can result in some other benefits. Preliminary research has revealed that fibre reinforced con-crete mixes prepared with cleaned recycled steel fibres are characterized by lower incidence of scaling when subjected to freezing and thawing cycles [14]. In addition, it was established that such fibre reinforced concrete is less susceptible to wearing and corrosion when exposed to ag-gressive marine environment [15, 16]. Therefore, recycled steel fibre reinforced concrete can be used for preparation of prefabricated elements in cases where a considerable resistance to bend-ing, and also to dynamic and impact load, is re-quired, such as prefabricated railway tracks on concrete bedding [17].

USE OF RECYCLED TEXTILE FIBRES

The last product of waste tyre recycling is textile fibres. These fibres have not so far found their use in construction industry. Preliminary research has shown that the influence of recycled textile fibres on the reduction of shrinkage due to drying is similar to that of industrial polypropylene fibres (Figure 6) [18]. If an increase in deformation due to concrete drying is compared with values for the same concrete without fibres, calculated ac-cording to Eurocode 2, it can be seen that the reduced shrinkage can be observed in the first days of the concrete matrix hardening process. When such recycled fibres are used, the con-crete shrinkage is visibly reduced, and hence the risk of cracking due to improper or insufficient curing is also lowered.

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Figure 6: hrinkage due to drying calculated according to EC2 for ordinary concrete, and measured for textile fibre reinforced concrete

In addition to reduced shrinkage due to drying, the recycled textile fibres have also some other positive influences on concrete durability, such as a higher resistance to penetration of chlorides and a reduced penetration of water. These re-sults show that the potential application of tex-tiles is in repair mortars, where it is extremely important to prevent occurrence of micro-cracks and penetration of aggressive substances.

CONCLUSION

Three types of materials are obtained in the waste tyre recycling process: rubber granu-lates, steel fibres, and polymer fibres. The way in which concrete properties are influenced by each of these materials, when used as second-ary raw materials, is explained in the paper. Rub-ber granules reduce compressive strength of concrete but, at the same time, they increase re-sistance to freezing and thawing, and the sound absorption capability. The addition of recycled steel fibres increases ductility of concrete, and prevents propagation of cracks. The addition of textile fibres reduces deformations due to shrink-age, and positively influences durability proper-ties of concrete. Taking into account their influ-ences on concrete, each of these materials can be used to prepare ecologically, technically and economically competitive alternative to products that are nowadays dominantly used in the engi-neering practice.

ACKNOWLEDGEMENT

The research presented in this paper was conduct-ed in the scope of project ‘’Rubberized Concrete

Noise Barriers’’, RUCONBAR ECO/10/277317, financed by the European Commission Eco-in-novation initiative, European Agency for Com-petitiveness and Innovation (EACI), and project ECOTRACK, financed by the BICRO agency in the scope of the Proof of Innovative Concept initiative. Special thanks are extended to the companies that have continuously supported re-search undertaken in this area: Viadukt d.d (TBP Pojatno), Gumiimpex – GRP d.o.o., Beton Lučko

d.o.o. and Holcim Croatia.

REFERENCES

Bjegović, D., Baričević, A., Lakušić, S.,

Damjanović, D., Duvnjak, I.: Positive in-

teraction of industrial and recycled steel fi-

bres in fibre reinforced concrete. Journal of

Civil Engineering and Management (2012).

(prihvaćen za objavljivanje).

Bjegovic, D., Baricevic, A., Lakusic, S.: Rub-

berized hybrid fibre reinforced concrete, In-

ternational Conference Microstructural - re-

lated Durability of Cementitious Composites,

RILEM Proceedings PRO 83. Amsterdam:

Rilem Publications s.a.r.l., 2012.

Bjegović, D., Baričević, A., Serdar, M.: Du-

rability properties of concrete with recycled

waste tyres // 12th International Conference

on Durability of Building Materials and Com-

ponents Porto, Faculdade de Engenharia

Universidade do Porto, 2011. pp. 1659-1667

Bjegović, D., Serdar, M., Jelčić Rukavina, M.,

Baričević, A.: Istraživanja kriterija održivosti

armiranog betona. GRAĐEVINAR (2010.)

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Council of the European Union, “Council Di-rective 1999/31/EC of 26 April 1999 on the land fill of waste,” 1999.

Čović, M. Optimalizacija svojstava mor-ta s različitim udjelima reciklirane gume, završni rad - preddiplomski studij. Zagreb : Građevinski fakultet, 11.09. 2012, 61 str. voditelj: Bjegović, D., neporedni voditelj: Baričević, A.

ETRMA – European tyre and rubber manu-facturers association, “End of life tyres - A valuable resource with growing potential,” 2010.

EU Projekt ‘’Rubberized Concrete Noise Bar-riers’’, RUCONBAR ECO/10/277317 www.ruconbar.com

Ganjian, E., Khorami, M., Maghsoudi, A.A.: Scrap-tyre-rubber replacement for aggregate and filler in concrete. Construction and Build-ing Materials (2009), 23(5), pp. 1828–1836.

Kovačević, J.: Promjena svojstava recikli-ranog hibridnog mikroarmiranog betona usli-jed izloženosti agresivnom okolišu / završni rad - diplomski/integralni studij. Zagreb, Građevinski fakultet, 14.02. 2013, 68 str. voditelj: Bjegović, D., neposredni voditelj: Baričević, A.

Lakušić, S., Baričević, A., Damjanović, D., Duvnjak, I., Haladin, I.: Kolosijek na betonskoj podlozi – ECOTRACK, Građenje prometne infrastrukture. Zagreb: Građevinski fakultet Sveučilišta u Zagrebu, Zavod za prometnice, 2012, pp. 7-49.

Marasović, I.: Utjecaj mikroarmiranja re-cikliranim vlaknima na svojstva betona / diplomski rad. Zagreb : Građevinski fakultet, 03.12. 2009, 120 str. voditelj: Bjegović, D., neposredni voditelj: Serdar, M.

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Mokos, I.: Procjena trajnosti mikroarmiranih betona u morskom okolišu primjenom po-tenciostatske anodne polarizacije / završni rad - diplomski/integralni studij. Zagreb : Građevinski fakultet, 14.02. 2013, 87 str. voditelj: Bjegović, D., neposredni voditelj: Baričević, A.

Neocleous, K., Angelakopoulos, H., Pilak-outas, K., Guadagnini, M.: Fibre - reinforced roller-compacted concrete transport pave-ments. Proceeding of the ICE – Transport (2011), 164(2), 97–109.

Petti, K., Marinac, L.: Betoni s otpadnim tek-stilnim vlaknima, Dekanova nagrada, Za-greb, Građevinski fakultet, 2010., voditelj: Bjegović, D., neposredni vodit

Serdar, M.; Baričević, A.; Lakušić, S.; Bjegović, D. Betonski proizvodi specijalne namjene od reciklata otpadnih guma. // Građevinar : časopis Hrvatskog saveza građevinskih inženjera. 65 (2013) , 9; 793-801

Skripkiūnas, G., Grinys, A., Janavičius, E.: (2010). Porosity and Durability of Rub-berized Concrete. http://www.claisse.info/2010%20papers/m55.pdf

Tlemat, H., Pilakoutas, K., & Neocleous, K. Stress-strain characteristic of SFRC us-ing recycled fibres. Materials andStructures (2006), 39, 365–377.

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Paper sent to revison: 07.02.2014.


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Paper number: 12(2014)1, 282, 95 - 99

BUILT ENVIRONMENT FRACTALITY AS A CRITERION OF SPACE MANAGEMENT

Maja Jevrić*Faculty of Civil Engineering, Podgorica, Montenegro

Dr Branislav PopkonstantinovićFaculty of Mechanical Engineering, Belgrade, Serbia

doi:10.5937/jaes12-5630

* Faculty of Civil Engineering, Cetinjski put bb, 81000 Podgorica, Montenegro; [email protected]

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In accordance with the holographic paradigm of the universe, recent studies indicate the importance of fractality of the human environment for his mental and physical well-being. There was awareness of that in the past, but the conventional methods of planning cities have forgotten that. The lack of hierarchy and human scale in modern cities, as so as its geometrically regular shapes and flattened lines, are associated with some negative social phenomena. Therefore, this paper aims to high-light the importance of fractality of built environment and to suggest the possibilities of its use as a criterion of space management.Key words: Fractals, Complexity, Space management, Decision making, Fractal dimension

INTRODUCTION

Parallel with revealing of fractal theory, com-plexity theory and chaos theory in the mid of XX century, and with the rapid advancement of tech-nology which has enabled further development of these theories, their frequent connecting with other scientific disciplines is evident. Introducing the chaos theory into urban planning requires a comprehensive change of the concept - requires awareness that there is not just one but a num-ber of possible scenarios for the future develop-ment and that it involves a number of deciding factors, as well as a large number of objectives.

Conventional methods of space management and planning have not shown as adequate to meet all the rapid changes in town, related to population size, lifestyle and technical-techno-logical development of infrastructure systems. For such a changable and complex system such as city, the traditional methods of analysis were insufficient because they did not treat the non-linearity of the problem and a large number of system parameters... Knowing that the manage-ment processes are interconnected with their results, i.e. result of one process becomes the input for another [01], the similarity with the pro-cess of generating fractals is obvious.

So far the cities have not been generally treated as complex systems. Planners, settlement build-ers and decision makers treated them as simple

predictive systems that needed to be arranged and reduced to their components for easier ur-ban modelling and urban problem solving. The conventional planning methods, based on the application of Euclidean geometry, have shown many disadvantages. [02]

The city is characterized by the complex orga-nization as a result of the interactions between its elements. It is an open system and its form and function continually change and affect the environment, as the environment affects them. Therefore, cities are perceived, more than any other human creation, as self-organized living systems, which can not be described by conven-tional linear and mechanical principles. Nikos Salingaros claims that degree of vitality of city depends on its possibility to achieve its own nat-ural complexity. [03]

Previous researches have shown that urban pat-terns have fractal structure. [02-08] The effects of the modern era, such as increasing car traffic, adversely affect the hierarchical principles typical for such structures, i.e. agglomerations become more uniformly shaped. The loss of physical complexity of built environment, as well as the lack of structures in human scale [09], adversely affects the human mind [02], what can be relat-ed to many negative trends (e.g. sense of alien-ation, occurrence of violence...). In this regard, the studies [02], [09] have given emphasis to the necessity of relationships and structures at all


Maja Jevrić - Built environment fractality as a criterion of space management

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scales of urban pattern, from the agglomeration level to the neighbourhood level and beyond - to the architectural details. Fractal principle can be recognized in this.

Fractal geometry as a „geometry of organized complexity“ is suitable for the description of complex systems such as cities. Since „fractal is a resulting image of the chaotic behavior of the system within a complex system“, the properties of fractals can be applied to the analysis of the forms of the city. [10]-[12] Measurements of frac-tal dimension of urban areas and urban bound-aries, can provide important input for planning of future development of the city. However, in this paper, we point out the possibility that fractality of built environment become one of the criteria of decision making in space management. Frac-tality, as a desirable feature of urban form, how-ever, may also be one of the objectives of the built environment management.

GOALS, OBJECTIVES AND CRITERIA OF MANAGEMENT

Effective management assumes a clear un-derstanding and definition of the different ob-jectives: basic and operational; short-term and long-term.

Management involves choosing the best or the satisfactory control action from a set of the avail-able ones. To make choosing possible, it is nec-essary to predefine criteria for comparison of control actions, so-called management criteria. On the basis of these criteria, selection, rank-ing of available control actions and selecting the best one can be done. Accordingly, it is very im-portant to choose the criterion that leads to the goal on the best way. The definition of criteria for specific control ac-tions is generally a very difficult problem, espe-cially when it comes to complex systems such as cities. In that case, many requests, often conflicting ones, which can not be captured by a single criterion, should be taken into account. [13] Then, so-called multicriteria decision mak-ing should be done, taking into account several criteria in solving management problems.

The problem becomes more complex if the de-scription criteria are considered, such as the quality of life in an urban environment, spirit of the place, feeling of satisfaction in a pleasant en-vironment, safety, etc. which are very difficult to quantify. Some studies [02, 03] speak in favour

of the observation that these qualities are asso-ciated with the complexity of built environment. So far it has not been possible to quantify these criteria, but analysis have show that fractal di-mension has got potential for it, in combination with some other parameters (e.g. lacunarity). However, the further investigations are neces-sary.

ABOUT FRACTALS

The term fractal describes the objects which are not geometrically regular at first sight. Eu-clidean geometry describes them as shapeless or amorphous but there is a certain order (pat-tern) found in their structure. „Fractal is irregu-lar or fragmented geometrical shape that can be divided into parts, whereas each of them is, at least aproximately, copy of the whole.“ [14] They mostly occur in nature, e.g. in the microstructure of DNA, crystals, plants, certain organs in hu-mans, clouds, mountains, lightning, coasts, gal-axy, in heartbeat fluctuations, weather forecast, earthquakes...

Figure 1: Examples of natural fractals



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However, as the “father of fractals”, Mandelbrot says that clouds are not spheres, mountains are not cones, coastlines are not circles, and bark is not smooth. Thus, neither Euclidean geometry, with its regular geometric shapes and integer di-mensions, can describe in the most appropriate

way the forms found in nature [14]. Therefore, fractal dimension (Df) is introduced to “measure” how well a structure fills the certain space. The street network in the city tends to reach every part of the city and each facility, so its fractality is unquestionable.

Figure 2: IFS and mathematical fractals

Fractals have the ability to summarize complex-ity, density and heterogeneity of space distribu-tion in a single value - fractal dimension, which is independent of the scale. [03-05]

The fractal dimension of the built environment de-scribes the distribution of structures in the plane of observation (ground plane or elevation) and can have values between 0 and 2. If Df = 2, it means that the urban pattern is uniform, while 0 corresponds to marginal case where the pattern is made of one point i.e. an isolated object. [08]

There are many methods for fractal dimension estimation. Most of them can be appropriate for the urban pattern analysis. All methods are based on the same principle of logarithmic equa-tion and tend to define a relationship between the object size and different scales of fractal di-mension estimation.

If the subject of the analysis is the image of the inhabited area (its ground plan), the calculation of its fractal dimension is based on the separa-tion of the occupied from the free pixels (the in-habited from the uninhabited areas) according to binary logic – assigning one colour to occupied

pixels and other colour to free pixels. For the es-timation of fractal dimension of built settlement in practice, ortophoto is used, prepared and processed as particular computer tool for fractal analysis (Benoit 1.3, Fractalyse, FracLac, Frac-top...) demands.

FRACTALITY OF URBAN PATTERN AS A CRITERION OF SPACE MANAGEMENT

Fractal structures are occured in many natural sistems. If the fractal principle is the principle by which nature is organized [14], then human be-ings are expected to perceive their environment in the same manner. Accordingly, human brain is fractal, too. People react to the level of complex-ity of what they see. [11] Fractality is an inherent property of human environment because of hu-man beings have been surrounded by fractals for millions of years, so, large part of the struc-ture of human mind comes from this ancient rela-tion. The environment, i.e. what human eyes can see, influences humans, thus the human mind is fractal. Only recently humans are surrounded by structures that are not fractal [02].

Figure 3: Aerial photo and scheme of African settlement (from [15])



In contrast to fractal natural structures, only in rare examples of built structures, mostly in tra-ditional architecture, fractality occurs. Traditional builders had a knowledge about fractal concept (in examples showed in Fig.3) when they con-sidered shape of settlements, as well as about respecting of human scale. In the modern cities design, the fractal concept is forgotten. The cit-ies characterized by straight lines of Euclidean geometry are planned for cars, more than for humans, so people lose their natural connection with the environment. How fractality of built envi-ronment could be used as a criterion for decision making in space management?

Fractal classification, i.e. zoning according to the value of fractal dimension, can help plan-ners to identify more precisely the boundaries of the zones where some interventions can be implemented to maintain complexity of the urban area. [11] If two neighbouring zones have differ-ent fractal dimensions, it can be a sign for pay-ing attention to that area, in order to get a more uniform complexity.

The determination of fractal dimension enables the estimation of the changes in physical com-plexity caused by particular project demands or interventions, which have a direct morphologi-cal influence on urban patterns, by comparing fractal dimension estimated before and after the “marked” change. [11] Based on this, it is pos-sible to gain insight into the obtained level of integration of the considered new building with the existing urban space. For example, a big in-tervention in space often has negative influence on the area complexity, what can be detected through fractal dimension decreasing.

Fractal dimension of urban boundary indicates fragmentation/compactness (related to the urban sprawl issue) of the urban patterns. The informa-tion about D

f of the urban boundaries and D

f of

the urban area can be used as a parameter for decision-making about spatial development. For example, when planning new residential areas, additional free areas are often used for further spatial development, which is not in accordance with the principles of rational space use.

Fractality of infrastructure networks can also be considered as a criterion of decision making. Since the fractal dimension of line “measures” how well the curve fills the certain space, fractality of traffic networks is a good indicator of its branching, i.e. the way the area is covered by roads.

Another possible form of the application of frac-tals is related to tax policy. Developing methods of application of fractals to assess the quality of urban entities or location would lead to provid-ing criteria for the tax amount determination, or policy of stimulating (or destimulating) to the use of a particular area.

CONCLUSION

Human natural environment (relief, galaxies, flora and fauna, natural phenomena...) is fractal. Since human beings have been surrounded by this fractal structures for the millions of years, it is not surprising that people lose this important relationship with their environment in their mod-ern, „anti-fractal“, cities. However, the importance of built environment fractality for human mental and physical well-being continue to be examined and proven. Although additional research on this issue is needed, in this paper we have tried to point out the reasons and the possibilities of us-ing fractality as a criteria in decision making pro-ces of space management.

Fractal dimension of an urban pattern shows how the area is filled by built structures. By chang-ing fractal dimension of the area, the change of complexity and heterogeneity of the built envi-ronment can be achieved. Varying the fractal dimension of urban boundaries can affect the prevention of the urban sprawl emergence and an irrational space consumption consequently. Further research is needed in terms of combin-ing the values of fractal dimension with the coef-ficient of land use or with some another urban parameters.

Fractality of built environment (ground plan of ur-ban pattern) is considered in only one (the first) projection here. That can be a useful tool in plan-ning process but further research should include analysis of the street elevation, appearance of the facade, city outline, street vistas...

REFERENCES

Batty, M. & Longley, M.: ,,Fractal Cities’’, Academic Press Limited, San Diego, CA and London, 1994.

Batty, M.: ,,Cities as Complex Systems: Scaling, Interactions, Networks, Dynamics and Urban Mor-phologies’’, www.casa.ucl.ac.uk, 20.10.2012.

Batty, M.: ,,The Size, Scale, and Shape of Cities’’, Science, 319 (5864), pp.769–771, 2008.

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Cooper, J. & Oskrochi, R.: ,,Fractal analy-sis of street vistas: a potential tool for as-sessing levels of visual variety in everyday street scenes’’, Environment and Planning B: Planning and Design, 01/2008, pp.349-363, 2008.

Eglash, R., Diatta, C.S. & Badiane, N.: ,,Frac-tal structure in Jola material culture’’, Ekis-tics 61, pp. 367-371, 1994.

Frankhauser, P. & Thomas, I.: ,,The mor-phology of built-up landscapes in Wallonia: a classification using fractal indices’’, www.math.univ-lille1.fr, 10.03.2013.

Frankhauser, P.: ,,Approaching urban pat-terns by fractal geometry : From theory to application’’, http://cddthema.univ-fcomte.fr ,15. 04. 2013.

Haghani, T.: ,,Fractal Geometry, Complex-ity and the Nature of Urban Morphological Evolution’’, www. fractalmorphology.com, 20.08.2011.

Jevrić M.: ,,Pristup proučavanju forme gra-da primjenom teorije kompleksnosti’’, In-ternational Conference GNP, Proceedings,

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Jevrić, M. & Kalezić, J.: ,,Fractals in urban space’’, Internacional Conference of Geom-etry and Graphics, Proceedings, Belgrade, pp. 186-195, 2010.

Jovanović, P.: ,,Upravljanje investicijama’’, Fakultet organizacionih nauka, Beograd, 2006.

Knežević, M.: ,,Upravljanje rizikom pri real-izaciji građevinskih projekata’’, phD diserta-tion, Građevinski fakultet, Beograd, 2005.

Mandelbrot, B.: ,,The Fractal Geometry of Nature’’, W. H. Freeman and Company, New York, 1983.

Radović, R.: ,,Forma grada’’, Osnove teor-ija i praksa, Orion Art-Stylos, Bg-Novi Sad, 2004.

Salingaros, N.: ,,Ecology and the Fractal Mind in the New Architecture’’, www.fractal.org, 20.04.2013.

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IX SYMPOSIUM - RESEARCH AND DESIGN IN COMMERCE AND INDUSTRY20th - 21st december, 2013

Editorial board of scientific journal of Applied Engineering Science in cooperation with Faculty of Mechanical engineering in Belgrade, organized IX symposium Research and design in commerce and industry, which was traditionally held during the month of December.

Objective of the Symposium was networking and experience sharing among experts from public companies in transport, energy and mechanical engineering sector with relevant reprensetatives of City and Republic institutions in order to promote, support and implement new technological devel-opments.

The areas covered by symposium were: planning and execution of projects in a wide range of indus-trial sectors such as transport, energy, construction, telecommunications, maintenance of technical systems, public sector enterprises, financial sector, IT sector etc...

Symposium primary presented the results of initiated or realized projects in domestic economy, as well as the knowledge, methods and techniques, standards and software tools that have contributed or could contributed to their better implementation.

The symposium IIPP, as in privious years, had plenary sessions, invited lectures, software demon-strations, magazines and book promotions...

The IX symposium was opened by prof. dr Jezdimir Knežević - MIRCE Akademy. Dr Jezdimir Knežević is a world class researcher, educator and entrepreneur. Over 300 publications dissemi-nated world-wide through books, papers, monographs and reports are attributed to his name. In ad-dition, he has delivered numerous technical presentations, key note addresses and speeches; has been congress, conference, symposium chairman, track leader, workshop presenter, round table moderator on many hundreds international events which took part in all six continents in over 40 countries. He has been elected as a Fellow, Member or Official of many leading Professional So-cieties and Institutions worldwide, and has been actively involved in editorial work with the world’s leading and prestigious referred journals and publishing houses. Dr Knezevic holds Bachelor, Master and Doctoral degree from Faculty of Mechanical Engineering, University of Belgrade, Yugoslavia. He shares life with Lynn, is passionate about motorsport, is challenged by rusty, but beautiful Lancia cars, and enjoys a thatched house in tranquil Devon, England, UK.

The accepted papers, was also represented by they authors and Proceedings with all accepted papers were published in electronic version.

Details: www.iipp.rs; +38111 6300 750; +38111 6300 751, +38111 3302 450.


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XXXIX SCIENTIFIC CONFERENCE MAINTENANCE OF MACHINERY AND EQUIPMENTBudva, 23rd-26th june, 2014 Hotel Slovenska plaza

ORGANIZERS

Faculty of Mechanical EngineeringUniversity of Belgrade

Serbian society of maintenance of technical systems

Institute for research and desing in commerce and industry

WELCOME TO XXXIX OMO 2014

Almost four decade, Faculty of Mechanical engineering in cooperation with their partners, organiz-es scientific conference - maintenance of machinery and equipment. The duration of the this con-ference and the trust by the participants, year after year, are confirming the importance of subjects

and the interest of professional and scientific community.

It is our wish for this year to exchange achieved scientific and professional experiences in the field of maintenance management of technical systems – the one we realized in practice as the one that

wait for better times.

Topics include the latest developments and guidelines in the field of production engineering and maintenance of technical systems, while special emphasis is given to the practical application of acquired knowledge. Program is balanced and focused on the needs of the commercial and aca-

demic world. All papers will be reviewed, which guarantees high quality of information and the pos-sibility of direct application.

As before and this time OMO is organized through exposure to original works, larger number of round table discussions and informal meetings.

We hope that, in the beautiful surroundings of the Adriatic coast, with common reasonableness and the culture of engineering, we will create solutions for better business for pride of generations

to come.

Prof. dr Branko Vasić


OMO 2014 THEMATIC AREAS

Industrial and infrastructure maintenance

Strategy of maintaining

Maintenance and production - technology, services, solutions and tools

Energy efficiency in industry

Safety, health and environmental protection

Risk management

TOPICS FOR ROUND TABLES

Keeping of competencesAsset management

*round tables will be organized from 25th-26th June, 2014

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PROGRAM COMMITTEE

Prof. dr Branko Vasić, MF, BeogradProf. dr Milorad Milovančević, MF, BeogradProf. dr Vladimir Popović, MF, BeogradProf. dr Jovan Todorović, MF, BeogradProf. dr Radivoje Mitrović, MF, BeogradProf. dr Ljubodrag Tanović, MF, BeogradProf. dr Miodrag Zec, FF, BeogradProf. dr Mirko Vujošević, FON, BeogradProf. dr Gradimir Danon, ŠF, BeogradProf. dr Slobodan Pokrajac, MF, BeogradDr Jezdimir Knežević, MIRCE Akademy, ExeterDoc. dr Dušan Milutinović, CIP, BeogradDr Predrag Uskoković, BVK, BeogradMr Milun Todorović, AUTOČAČAK, ČačakDipl. inž. maš., Dragan Jovanović, Direktor KOLUBARA METAL Dipl. inž. saob., Radmilo Petrović, SP LASTA

ORGANIZING COMMITTEE

Prof. dr Vojkan Lučanin, MF, BeogradMiloš Vasić, MF, BeogradNada Stanojević, iipp, BeogradMiloš Petrović, iipp, BeogradDarko Stanojević, MF, BeogradMiloš Dimitrijević, iipp, BeogradIvana Spasojević, iipp, BeogradMilica Mikić, iipp, BeogradMilisav Krstović, Generalni direktor JPKP LazarevacDušan Đurašević, Generalni direktor Euro Sumar

Siniša Lazarević, Generalni direktor

Gradske čistoće Beograda

Slobodan Radomirović, Generalni direktor SP

Lastra

THE REGISTRATION FEE

The registration fee for participation in the symposium is 150 euros.

The registration fee include:attendance NSS OMO 2014.handoutcocktailsexcursion

Members of the academic community are paying 50% of the registration fee.

Students and postgraduate students are paying 25% of the registration fee.

Companions who do not participate in the conference are paying 25% of the registration fee which includes the contents of a common nature such as cocktails and excursion.

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MORE INFORMATIONS

www.iipp.rs; +38111 6300 750; [email protected]

A N N O U N C E M E N T O F E V E N T S


B O O K R E C O M M E N D A T I O N

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Recommended by MSc Darko Stanojević

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106

Nenad Fric, Dr Dragan Buđevac, Dr Zlatko Marković, Jelena Dobrić, Dr Jovan Isaković

SPOJNA SREDSTVA SISTEMA “HUCK BOBTAIL” – NOVO REŠENJE ZA VISOKOVREDNE

ZAVRTNJEVE SA ZAKLJUČAVANJEM

107

Dr Victor Vasilievich Elistartov, Dr Miloš Knežević, Roman Denisov, Michael Konishchev

PROBLEM GRAĐENJA VIND-DIZEL ELEKTRANA U SUROVIM KLIMATSKIM USLOVIMA107

Darya Nemova, Vera Murgul, Viktor Pukhkal, Alex Golik, Eugene Chizhov, Nikolay Vatin

REKONSTRUKCIJA ADMINISTRATIVNIH OBJEKATA 70-ih: MOGUCNOSTI

ENERGETSKE MODERNIZACIJE

108

Dr Luisa María Gil Martín, Dr Enrique Hernández Montes

OPTIMIZOVANJE POPREČNOG PRESEKA U CILJU MINIMIZIRANJA

UTROŠENE ENERGIJE

108

Dr Miroslav Premrov, Boštjan Ber, Dr Andrej Štrukelj

DEFORMACIONA OTPORNOST PREFABRIKOVANIH DRVENO-STAKLENIH

ZIDNIH ELEMENATA

109

Anka Starčev Ćurčin, Dr Đorđe Lađinović, Aleksandra Radujković, Andrija Rašeta

PRORAČUN AB VIŠESPRATNOG RAMA PRIMENOM METODE PROGRAMIRANOG

PONAŠANJA SA ASPEKTA KAPACITETA PREMA EN1998-1

109

Marijana Lazarevska, Milivoje Milanović, Dr Miloš Knežević, Dr Meri Cvetkovska, Ana Trombeva Gavrilovska, Dr Todorka Samadzioska

VEŠTAČKA NEURONSKA MREŽA ZA PREDVIĐANJE POŽARNE OTPORNOSTI

KOMPOZITNIH STUBOVA

110

Dr Ivana Štimac Grandić

UTICAJ GUSTOĆE MERNIH PODATAKA NA OTKRIVANJE OŠTEĆENJA GREDA

POMOĆU UTICAJNIH LINIJA PROGIBA

110

S A D R Ž A J


S poštovanjem,


Dekan građevinskog fakulteta u Podgorici Predsednik Organizacionog Odbora GNP 2014 Konferencije

O D U R E Đ I V A Č K O G O D B O R A

111Dr Marko Pavlović, Dr Milan Spremić, Dr Zlatko Marković, Dr Dragan Buđevac, Dr Milan VeljkovićSAVREMENA ISTRAŽIVANJA SMIČUĆEG SPOJA PREFABRI-KOVANIH SPREGNUTIH GREDA OD ČELIKA I BETONA

111

Dr Cristina Campian, Alina Haupt-Karp, Maria Pop, Dr Nicolae Chira, Gabriel Urian, Dr Paul Pernes

PONAŠANJE POTPUNO OBLOŽENIH ČELIK-BETON SPREGNUTIH STUBOVA PRI MONOTONOM I CIKLIČNOM OPTEREĆENJU

112Dr Marijana Serdar, Ana Baričević, Dr Dubravka Bjegović, Dr Stjepan Lakušić

MOGUĆNOSTI UPOTREBE RECIKLATA OTPADNIH GUMA U BETONSKOJ INDUSTRIJI

112Maja Jevrić, Dr Branislav Popkonstantinović

FRAKTALNOST GRAĐENE SREDINE KAO KRITERIJUM UPRAVLJANJA PROSTOROM

105

XXI vek biće vek inženjera.

Peti put na Žabljaku, tradicionalno, održan je skup Građevinarstvo-nauka i praksa, sa željom da svoja naučna i stručna dostignuća razmenimo – i ona koja smo materijalizovali u prostoru, kao i ona koja čekaju bolja vre-mena. Horizonte skupa GNP, ovog puta čini 271 rad recenziran i odabran za publikovanje, koje potpisuje 511 autora iz čak 20 zemalja sveta. Kao i do sada i ovog puta je organizovan veći broj okruglih stolova koji obuh-vataju aktuelnu problematiku. Jedan od njih je obrazovanje u graditeljst-vu jer edukacija inženjera predstavlja ulaganje u budućnost, a naročito u XXI veku koji će biti vek inženjera.Bez postignutog kvaliteta u oblasti Prof. dr Miloš Knežević

obrazovanja ne može se pružiti odgovarajući odgovor na vreme koje je pred nama, a ono nalaže oz-biljne pristupe edukaciji. U tom smislu zaključena je neophodnost kontinuiranog obrazovanja tokom celog života koje ima svoje duboke korene i predstavlja dobru praksu u inženjerstvu najuglednijih evropskih tehničkih univerziteta. GNP, kao i svaki naš posao, ne bi bio kvalitetan bez učešća onih kojima prenosimo znanja i veštine. Zbog toga su sa nama na Žabljaku bili i studenti i tek diplomirani inženjeri sa svojim prezentacijama i vizijama. Nadamo se da ćemo u vremenu koje je pred nama, zajedničkom umnošću i kulturom graditeljstva stvarati objekte na ponos generacijama koje dolaze. Zahvaljujemo članovima Naučnog odbora i autorima, a posebno sponzorima i prijateljima koji su nas podržali u organizaciji i pomogli održavanje Skupa GNP 2014. Bez njihove pomoći, ovo se ne bi moglo realizovati.

S A D R Ž A J


R E Z I M E I R A D O V A

106

doi:10.5937/jaes12-5609 Broj rada: 12(2014)1, 268Originalni naučni članak

U većini evropskih zemalja, uključujući i Rusiju, svedoci smo konstantnog pooštravanja

zahteva za toplotnom zaštitom objekata. Zgrade istorijskih objekata preko noći su postale

“energetski neefikasne” i potrebna im je modernizacija, u cilju smanjenja potrošnje energije, posebno

za poboljšanje termalne zaštitne spoljasnjih elemenata konstrukcije . Medjutim, za razliku od masovnih

serija,u istorijskim objektima su opste priznate kulturne, istorijske i arhitektonske vrednost. Gubitak is-

torijske autentičnosti starih objekata kao rezultat energetski efikasne modernizacije je nedopustiv. U

tekstu se razmatra primenjivost postojećih standarda u projektovanju toplotne zaštite istorijskih objekata.

Konkretno, uzimaju se u obzir sve “za” i “protiv” termoizolacije spoljasnjih elemenata konstrukcije kada su

u pitanju objekti od istorijskog znacaja. Predlaže se da je potrebno da se očuva ne samo spoljašnji izgled

objekata - spomenika istorije i kulture, vec i istorijski sistem gradnje. Takođe se predlaze da se prebaci

akcent sa “uštede po svaku cijenu” na poboljšanje kvaliteta mikroklime u stambenim zgradama.

Ključne reči: Toplotna izolacija, Termalna izolacija, Rekonstrukcija, Modernizacija, Istorijski objekti,

Energetska efikasnost

OSOBENOSTI ENERGETSKI EFIKASNE MODERNIZACIJE ISTORIJSKIH OBJEKATA (NA PRIMERU SANKT-PETERBURGA)

doi:10.5937/jaes12-5663 Broj rada: 12(2014)1, 269Pregledni članak

Vera Murgul - Institut za građevinsko inženjerstvo, Sant Petersburg, Rusija

OBRAZOVANJE INŽENJERSKOG KADRA U OBLASTI GRAĐEVINARSTVA

Privredni rast je presudno važan za prosperitet jednog društva i njegovih članova, a on se temelji na kvalitetnoj

i kompetentnoj radnoj snazi. Obrazovani i sposobni ljudski resursi su jedan od ključnih faktora koji opredjeljuju

poziciju nacionalne ekonomije u međunarodnoj zajednici. Adekvatno uređen obrazovni sistem i dostupnost ob-

razovanja, kao i kultura »društva koje uči« je generator ekonomskog kulturnog i opšte-društvenog napretka.

Ključne reči: Agencija za zapošljavanje Republike Crne Gore, Ljudski resursi; Građevinsko

inženjerstvo, Inženjeri, Obrazovanje

Dr Nevenka Pavličić - Građevinski fakultet, Univerzitet u Podgorici, Crna Gora

Dr Mladen Perazić - Poslovna škola u Crnoj Gori, Univerzitet Mediteran, Crna Gora

Dr Dragana Đurić-Jocić - Fakultet za medije i komunikacije, Univerzitet Singidunum, Srbija

Dr Miloš Knežević - Građevinski fakultet, Univerzitet u Podgorici, Crna Gora

doi:10.5937/jaes12-5631 Broj rada: 12(2014)1, 270Originalni naučni članak

EKSPERIMENTALNA OCENA PARAMETARA TOPLOTNOG FLUKSA GREJNIH TELA

Viktor Pukhkal - Fakultet ekološkog inženjerstva i opštinskih objekata, Arhitektonski i građevinski Univerzitet u Sant Peteserburgu, Sant Petersburg, Rusija

Za razvijanje efikasnih sistema grejanja, obezbedjujucih normativne uslove u prostorijama pri mini-

malnoj potrosnji energije, moramo da znamo raspodelu radiacionih i konvektivnih flukseva toplote

od grejnih tela. Razradjen je i opisan metod istrazivanja. Izucavana su grejna tela (konvektor radi-

jator) sistema za grejanje na vodu. Prikazani su rezultati merenja toplotnog fluksa grejnih tela.

Opredeljene su konvektivne i radiacione komponente toplotnog fluksa grejnih tela

Ključne reči: Konvektivni fluks zračenja, Toplotni fluks zračenja, Grejna tela, Grejanje



doi:10.5937/jaes12-5611 Broj rada: 12(2014)1, 271Stručni članak

SPOJNA SREDSTVA SISTEMA “HUCK BOBTAIL” – NOVO REŠENJE ZA VISOKOVREDNE ZAVRTNJEVE SA ZAKLJUČAVANJEM

Firma “Alcoa Fastening Systems” konstruisala je “Huck BobTail” sistem mehaničkih spojnih sred-

stava i predstavila ga kao jednu od najnaprednijih tehnologija spajanja do danas. Prepoznat kao

zaključavajući zavrtanj (antivandal) naredne generacije, “Huck BobTail” donosi pet puta veću čvrstoću

na zamor od standardnih zavrtnjeva sa navrtkom, a konstruisan je tako da pruži visoku čvrstoću,

pouzdanost i otpornost na vibracije i u najekstremnijim uslovima. Konstruisan da zadovolji širok spe-

ktar sistema za spajanje, “BobTail” odlikuju visoke performance kao i jednostavna i brza ugradnja.

Ključne reči: Antivandal zavrtnjevi, Visokovredni zavrtnjevi, “Huck BobTail” zavrtnjevi

Nenad Fric - Građevinski fakultet, Univerzitet u Beogradu, Srbija

Dr Dragan Buđevac - Građevinski fakultet, Univerzitet u Beogradu, Srbija

Dr Zlatko Marković - Građevinski fakultet, Univerzitet u Beogradu, Srbija

Jelena Dobrić - Građevinski fakultet, Univerzitet u Beogradu, Srbija

Dr Jovan Isaković- Tehnikum Taurunum-Fakultet primenjenih inženjerskih nauka, Beograd, Srbija

doi:10.5937/jaes12-5632 Broj rada: 12(2014)1, 272Originalni naučni rad

Dr Victor Vasilievich Elistratov - Institut za građevinsko inženjerstvo, Sant Petersburg, Rusija

Dr Miloš Knežević - Građevinski fakultet, Univerzitet u Podgorici, Crna Gora

Roman Denisov - Institut za građevinsko inženjerstvo, Sant Petersburg, Rusija

Michael Konishchev - Institut za građevinsko inženjerstvo, Sant Petersburg, Rusija

PROBLEM GRAĐENJA VIND-DIZEL ELEKTRANA U SUROVIM KLIMATSKIM USLOVIMA

Napajanje tokom gradnje na osnovu obnovljivih izvora energije javlja se aktuelnim problemom savremene grad-

jevinske nauke. Najaktuelniji i najperspektivniji pravac energetike obnovljivih izvora energije kako u Rusiji tako i

u Srbiji javlja se energija vetra. U severnim regionima , poboljšanje pouzdanosti i efikasnosti napajanja je pred-

lozeno da se resi izgradjnom vetro-dizel elektrana (VDE) s optimizacijom sastava parametara i rezima rada.

Članak opisuje glavne probleme u izgradnji VDE u surovim klimatskim uslovima. Sloznosti u vezi sa upotrebom i izgradnjom vetro-elektrana. To su problemi transporta, izgradnja na vecnom ledu, instalacija i podesavanje op-reme za surove klimatske uslove. U clanku su opisani osnovni zadaci, cije resavanje ce povecati pouzdanost u radu. Rasmotreni su brojni problemi i predlozena resenja pri izradi projektne dokumentacije za izgradnju VDE u Jamalsko-Nenečkom autonomnom okrugu. Opisane su preporuke za odabir osnovne opreme. Parametri VDE sa visokim stepenom supstitucije optimizovani koriscenjem softverskog paketa Homer 2.81.Ključne reči: Surovi klimatski uslovi, Izgradnja, Vetro-elektrana, Vetro-dizel elektrane, Energetski efikasne tehnologije u izgradnji



REKONSTRUKCIJA ADMINISTRATIVNIH OBJEKATA 70-ih: MOGUCNOSTI ENERGETSKE MODERNIZACIJE


Darya NemovaInstitut za građevinsko inženjerstvo, Politehnički Univerzitet u Sant Petesburgu, Sant Petesburg, Rusija

Vera MurgulInstitut za građevinsko inženjerstvo, Politehnički Univerzitet u Sant Petesburgu, Sant Petesburg, Rusija

Viktor PukhkalFakultet ekološkog inženjerstva i opštinskih objekata, Arhitektonski i građevinski Univerzitet u Sant Peteserburgu, Sant Petersburg, RusijaAlex GolikInstitut za građevinsko inženjerstvo, Politehnički Univerzitet u Sant Petesburgu, Sant Petesburg, Rusija

Eugene Chizhov Institut za građevinsko inženjerstvo, Politehnički Univerzitet u Sant Petesburgu, Sant Petesburg, Rusija

Nikolay VatinInstitut za građevinsko inženjerstvo, Politehnički Univerzitet u Sant Petesburgu, Sant Petesburg, Rusija

Pitanje energo-efikasnosti i uštede energije ima visok stepen aktuelnosti. Utvrđeno je da sa tačke

gledišta velike potrošnje toplotne energije administrativni objekti koji su izgrađeni u Rusiji do 1996.

godine zahtevaju modernizaciju. Ugrađene u svoje vreme, i na osnovu, u to vreme aktuelnih stan-

darda termičke zaštite, u sadašnje vreme ti objekti automatski su postali nezadovoljavajući sa te

tačke gledišta. U isto vreme njihov period eksploatacije nije završen, što znači da tim objektima nije

potreban kapitalni remont. U radu navodimo kratak izveštaj termovizijskog ispitivanja zgrade kao

i sistema za grejanje i ventilaciju. Takođe je predstavljen kompleks mera za smanjenje potrošnje

energije u zgradi do normativnog, pri tom ne “otpravljajući” objekt na kompleksnu rekonstrukciju i po

mogućnosti bez obustavljanja radnih procesa unutar objekta. Kao glavni kriterijum pri izboru opcije

za izolaciju spoljašnjih zidova predloženo je da se koristi period otplate izolacije.

Ključne reči: Period otplate, Toplotna provodljivost, Termo-izolacija, Ušteda energije, Energetska

efikasnost


Dr Luisa María Gil MartínCampus Universitario de Fuentenueva, Univerzitet u Granadi, Granada, Španija

Dr Enrique Hernández MontesCampus Universitario de Fuentenueva, Univerzitet u Granadi, Granada, Španija

OPTIMIZOVANJE POPREČNOG PRESEKA U CILJU MINIMIZIRANJA UTROŠENE ENERGIJE

U cilju smanjenja emisije CO2, inženjeri i arhitekte moraju optimizovati upotrebu materijala, pogoto-

vo čelika, kako bi potrošnja bila optimalna. Moguće je obezbediti otpornost konstruktivnog elementa

uz smanjenje količine čelika koji će biti adekvatno lociran u poprečnom preseku, uz podizanje na viši

nivo kontrole na gradilištu.

Ključne reči: Ušteda čelika, Utrošena energija, Održiva gradnja



Dr Miroslav PremrovGrađevinski fakultet, Univerzitet u Mariboru , Maribor, Slovenija

Boštjan BerKager hiša DOO, Ptuj, Slovenija

Dr Andrej ŠtrukeljGrađevinski fakultet, Univerzitet u Mariboru , Maribor, Slovenija

DEFORMACIONA OTPORNOST PREFABRIKOVANIH DRVENO-STAKLENIH ZIDNIH ELEMENATA

Značaj ugradnje velikih staklenih površina u drvene konstrukcije značajno je porastao u posljedn-

jih deset godina. To je bio jedan od glavnih razloga za sprovođenje prikazanog eksperimentalnog istraživanja na drvenim konstrukcijama sa fiksnim zastakljenjem na spoljašnjim stranama ili u sredini zidnih elemenata sa drvenim okvirom. Drveni okvir, zajedno sa staklenim pločama direktno spo-

jenim za njega, čine kompozitni zidni element, koji svojom nosivošću poboljšava stabilnost cijelog

sistema. Korišćene su različite vrste ljepila posebnih karakteristika, koji su izazivali različite uticaje

na zid kompozita. Predstavljena su dva koncepta, jedan s bilateralnim staklom, a drugi sa staklenom

oblogom u sredini profila.

Ključne reči: Monotoni testovi, Eksperimenti, Stabilnost, Otpornost, Staklo, Drvo

Anka Starčev-ĆurčinFakultet tehničkih nauka, Univerzitet u Novom Sadu, Novi Sad, Srbija

Dr Đorđe LađinovićFakultet tehničkih nauka, Univerzitet u Novom Sadu, Novi Sad, Srbija

Aleksandra RadujkovićFakultet tehničkih nauka, Univerzitet u Novom Sadu, Novi Sad, Srbija

Andrija RašetaFakultet tehničkih nauka, Univerzitet u Novom Sadu, Novi Sad, Srbija

doi:10.5937/jaes12-5670 Paper number: 12(2014)1, 276

PRORAČUN AB VIŠESPRATNOG RAMA PRIMENOM METODE PROGRAMIRANOG PONAŠANJA SA ASPEKTA KAPACITETA PREMA EN1998-1

Metoda programiranog ponašanja zahteva duktilnost nosećih armiranobetonskih elemenata i predviđa gredni mehanizam plastifikacije kako bi konstrukcija bila u stanju da apsorbuje znatnu seizmičku

energiju. Posebno su pogodni statički neodređeni sistemi kod kojih broj statičke neodređenosti određuje broj plastičnih zglobova koji se formiraju, a time se postiže povoljna disipacija energije. U radu je dimenzionisan armiranobetonski petospratni ram za dve klase duktilnosti prema propisima EN1992-1-1 i EN1998-1.

Originalni naučni rad

109



Marijana Lazarevska*Građevinski fakultet, Univerzitet u Skoplju, Skoplje, Makedonija

Milivoje MilanovićDržavni univerzitet u Novom Pazaru, Novi Pazar, Srbija

Dr Miloš KneževićGrađevinski fakultet, Univerzitet u Podgorici, Podgorica, Crna Gora

Dr Meri CvetkovskaGrađevinski fakultet, Univerzitet u Skoplju, Skoplje, Makedonija

Ana Trombeva GavriloskaGrađevinski fakultet, Univerzitet u Skoplju, Skoplje, Makedonija

Dr Todorka SamadžioskaArhitektonski fakultet, Univerzitet u Skoplju, Skoplje, Makedonija


VEŠTAČKA NEURONSKA MREŽA ZA PREDVIĐANJE POŽARNE OTPORNOSTI KOMPOZITNIH STUBOVA

U radu je prezentirana primena prognoznog modela na bazi neuronskih mreža za predviđanje požarne

otpornosti centrično opterećenih spregnutih stubova opožarenih sa svih strana. Primenom kompjut-

erskog programa FIRE analizirani su tri tipa spregnutih preseka: potpuno ubetonirani, delimično

ubetonirani, cevkasti profil ispunjen betonom i referentni klasični AB stub. Analiziran je uticaj oblika,

dimenzije preseka i intenzitet opterećenja na požarnu otpornost stubova. Rezultati numeričke anal-

ize poslužili su kao ulazni parametri za treniranje neuronske mreže.

Ključne reči: Kompozitni stubovi, Požarna otpornost, Model prognoziranja, Veštačke neuronske

mreže

Dr Ivana Štimac GrandićGrađevinski fakultet, Univerzitet u Rijeci, Rijeka, Hrvatska



UTICAJ GUSTOĆE MERNIH PODATAKA NA OTKRIVANJE OŠTEĆENJA GREDA POMOĆU UTICAJNIH LINIJA PROGIBA

U radu je istražen utjecaj gustoće mjernih podataka na pouzdanost otkrivanja i likalizacije oštećenja

metodom zasnovanom na usporedbi utjecajnih linija progiba i njihovih derivacija (nagiba i zakrivljen-

osti) za neosštećeno i oštećeno stanje konstrukcije. Numerički primjeri, u kojima je variran razmak

mjernih podataka i njihov položaj u odnosu na oštećenje, provedeni su na jednostavnoj gredi s jed-

nim oštećenjem.

Ključne reči: Gustoća mernih podataka, Uticajna linija progiba, Greda, Otkrivanje oštećenja




Dr Marko PavlovićGrađevinski fakultet, Univerzitet u Beogradu, Beograd, Srbija

Dr Milan SpremićGrađevinski fakultet, Univerzitet u Beogradu, Beograd, Srbija

Dr Zlatko MarkovićGrađevinski fakultet, Univerzitet u Beogradu, Beograd, Srbija

Dr Dragan BuđevacGrađevinski fakultet, Univerzitet u Beogradu, Beograd, Srbija

Dr Milan VeljkovićLuleå Tehnološki Univerzitet, Švedska

SAVREMENA ISTRAŽIVANJA SMIČUĆEG SPOJA PREFABRI-KOVANIH SPREGNUTIH GREDA OD ČELIKA I BETONA

Prefabrikacijom spregnutih konstrukcija od čelika i betona može se povećati njihova konkurentnost

i održivost. Ovde su prikazana istraživanja podužnih smičućih spojeva koja su nedavno sprovedena

na Građevinskom fakultetu Univerziteta u Beogradu. Grupisani moždanici sa glavom i zavrtnjevi

kao sredstva za sprezanje koja su pogodna za prefabrikaciju spregnutih konstrukcija su ispitivani

standardnim eksperimentom smicanja. Eksperimentalno je ispitano ukupno 30 uzoraka i vršene su

analize na bazi MKE korišćenjem softverskog paketa Abaqus/Explicit. Na bazi ekserimentalnih i

numeričkih ispitivanja izvršeno je poređenje ponašanja ova dva sredstva za sprezanje.Ključne reči: Zavrtnjevi kao sredstva za sprezanje, Grupisani moždanici, Montažne spregnute grede

Dr Cristina CampianTehnički univerzitet u Cluj-u, Cluj-Napoca, Rumunija

Alina Haupt-KarpTehnički univerzitet u Cluj-u, Cluj-Napoca, Rumunija

Maria PopTehnički univerzitet u Cluj-u, Cluj-Napoca, Rumunija

Dr Nicolae ChiraTehnički univerzitet u Cluj-u, Cluj-Napoca, Rumunija

Gabriel UrianTehnički univerzitet u Cluj-u, Cluj-Napoca, Rumunija

Dr Paul PernesTehnički univerzitet u Cluj-u, Cluj-Napoca, Rumunija

doi:10.5937/jaes12-5672 Broj rada: 12(2014)1, 280 Originalni naučni rad

PONAŠANJE POTPUNO OBLOŽENIH ČELIK-BETON SPREGNUTIH STUBOVA PRI MONOTONOM I CIKLIČNOM OPTEREĆENJU

U radu je predstavljen numerički model razvijen za potpuno obložene čelik-beton spregnute stubove pri monotonom i cikličnom opterećenju. Numerički model je urađen programom FineLg, razvijenim na ArGenCo odsjeku Univerziteta u Liježu. Validacija modela je urađena na pet eksperimentalnih testova preuzetih iz internacionalne literature: dva sa Tehničkog univerziteta Kluž-Napoka i po jedan sa Tajvana, iz SAD-a i iz Kine. U eksperimentima su korišćeni betoni normalnih i visokih čvrstoća. Različiti parametri su upoređeni u radu: djelimičnia i potpuna duktilnost, disipacija energije, otpornost i koeficijent krutosti.

Ključne reči: Numerički model, Potpuno obloženi čelik-beton spregnuti stubovi

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doi:10.5937/jaes12-5671 Broj rada: 12(2014)1, 281

Dr Marijana SerdarGrađevinski fakultet, Univerzitet u Zagrebu, Zagreb, Hrvatska

Ana BaričevićGrađevinski fakultet, Univerzitet u Zagrebu, Zagreb, Hrvatska

Dr Dubravka BjegovićGrađevinski fakultet, Univerzitet u Zagrebu, Zagreb, Hrvatska

Dr Stjepan LakušićGrađevinski fakultet, Univerzitet u Zagrebu, Zagreb, Hrvatska

MOGUĆNOSTI UPOTREBE RECIKLATA OTPADNIH GUMA U BETONSKOJ INDUSTRIJI


U radu je prikazan uticaj reciklata otpadnih guma, upotrebljenih kao sekundarne sirovine, na svojst-va betona. Tek kada se uzmu u obzir specifična svojstva svakog pojedinog reciklata otpadnih guma, moguće ih je upotrebiti u betonskoj industriji za pripremu betonskih proizvoda specijalnih svojstava. Proizvodi koji sadrže reciklate otpadnih guma tada mogu biti ekološki, tehnološki i ekonomski kom-petitivna alternativa klasičnim proizvodima koji se koriste u inženjerskoj praksi.Ključne reči: Tekstilna vlakna, Čelična vlakna, Gumene granule, Reciklati guma

Broj rada: 12(2014)1, 282

Maja JevrićGrađevinski fakultet, Podgorica, Crna Gora

Dr Branislav PopkonstantinovićMašinski fakultet, Beograd, Srbija

doi:10.5937/jaes12-5630Originalni naučni rad

FRAKTALNOST GRAĐENE SREDINE KAO KRITERIJUM UPRAVLJANJA PROSTOROM

U skladu sa holografskom paradigmom univerzuma, novija istraživanja ukazuju na važnost fraktal-nosti ljudskog okruženja za njegovo mentalno i fizičko dobrostanje. Primjeri starijih naselja, gdje je fraktalni koncept primjenjen, pokazuju da je u prošlosti postojala svijest o tome, a koja je u konven-cionalnim metodama planiranja gradova zaboravljena. Nedostatak hijerarhičnosti i čovjekomjerne razmjere, geometrijski pravilni oblici i zaravnjene linije modernih gradova, vezuju se za negativne društvene pojave. Stoga ovaj rad ima za cilj da ukaže na važnost fraktalnosti građene sredine i da predloži mogućnosti njenog korišćenja kao kriterijuma upravljanja prostorom.Key words: Fractal dimension, Decision making, Space management, Complexity, Fractals


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1 2014 12 jaes