Construction Techniques - 3

7/24/2019 Construction Techniques - 3

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Diploma Level

Environmental Science and Construction Techniques 3

Construction Techniques 3

1.0 Site Works

1.1 Site nvesti!ation Once a site has been selected by a developer for a new building project, the suitability of that site for

that particular project must be fully investigated

The investigation must be carried out irrespective of whether the site has been previously developedand the buildings are still in existence or have been demolished or the site has never previously been

built upon.

There are two types of site investigation

(l) That carried out by the client and architect for the purpose of determining the feasibility ofthe site for its proposed purpose

Eg. (i) eather the buildings could be most economically positioned having regard to

foundation(ii) Topography

(iii) !ervices

(iv) "djacent building

(v) "ccess

(ll) That carried out by the builder or contractor for the purpose of preparing an accurate tender

# " certain amount of the information obtained in (a) will be passed to the builder or madeavailable for his inspection

1.1.1 "ethod o# Site nvesti!ation

!ite visit

$rom the existing date

%aps

$rom the local authorities &y monitoring the closer building

1.1.$ What is the in#ormation to %e collected&

'round water condition

$lood detail

Earlier use of the land

loser building behavior

"ccess to the site

!ervices available

"!! *nternational +etwors (vt) -imited.Eng. T. !uthaaran


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&!cEng. '/ip. (!tru. Eng), "%*E (!-)

Diploma Level


Construction Techniques 3Soil E'ploration

!ubsurface conditions at any given site must be ade0uately explored to obtain information re0uired

in design and construction of foundations

The investigations may range in scope from a simple examination of the surface soil with a fewshallow trail pits O1

" detailed study of the soil and groundwater conditions to a considerable depth below the surface by

means of bore holes.

The extent of the wor depends on the importance and foundation arrangement of the structure, the

complexity of the soil condition and the information which may be available on the behaviour of theexisting foundation on similar soil.

" detailed site investigation involving deep bore holes and laboratory testing of soils is always

necessary for heavy structures lie bridges, multistory building and industrial plants.

The purpose o# soil e'ploration

$or new structuresi. The type and depth of foundation can be selected

ii. The bearing capacity of the selected foundation can be determined

iii. The settlement can be predicted

iv. The ground water level can be establishedv. The earth pressure against walls and abutments can be evaluated

vi. "de0uate provisions can be made against possible construction difficulties,

$or existing structures

i. The safety if the structure can be investigated

ii. $urther settlement can be predicted

iii. 1emedial measures can be suggested if the structure is unsafe or liely to suffer detrimentalsettlement

$or highways and air fieldsi. The roads and runways can be located or aligned properly

ii. &arrow pits can be selected and properly located

iii. /itches, culverts and drains can be suitably locatediv. The need and type of sub#grade treatment can be determined

-ocal nearby sources of the construction materials can be ascertained

What is the in#ormation (e can !et #orm the la%orator) test

ompaction ratio &1 (alibonia &earing 1atio)

!hear !trength

%oisture ontent

ermeability

onsolidation rate


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&!cEng. '/ip. (!tru. Eng), "%*E (!-)

Diploma Level


Construction Techniques 3"ethod o# Site E'ploration

The various methods of site explorations may be grouped as follows3

# Open trial pits

# &orings# 'eophysical investigations

# !ubsurface soundings

*pen Trial +its

its are dug at the site exposing the subsoil surface thoroughly

This method is enable a clear picture to be obtained of the stratification of the soil and the presence

of any lenses or pocets of weaer material

This method is generally suitable and cheapest for small depths (up to 4 m)

'reater depths and bellow to ground water table, this method becomes expensive since special

measures for lateral supports and ground water lowering become inevitable

,orin!

The different methods of boring or drilling are as given below3

-i "uger boring

-ii ash boring

-iii ercussion boring

-iv 1otary boring

-i /u!er ,orin!

!uitable for soft soils above the water table that have sufficient cohesion to stand unsupported in an

unlined borehole

5and augers are used for depths up to about 6 m

%echanically operated augers are used for greater depths and can also be used in gravel soils.

-ii Wash ,orin!

*n this method, water is forced under pressure through an inner tube which may be rotated or moved

up and down inside a casing pipe

The chopping and jetting action of the bit and water disintegrates the soil

The soil water slurry comes up to the ground through the annular space between the drill rod and the

casing

The slurry flowing out gives an indication of the soil type

*n this method heavier particle of different soil layers remain under suspension in the casing pipe andget mixed up

This method is unsuitable for obtaining reliable samples for classification

henever a sample is to be taen, washing should be stopped and a tube sampler should be attached

to the end of the drill rod or the inner tube

&y driving the sampler into the soil, by hammering or jacing, samples can be taen

"!! *nternational +etwors (vt) -imited.

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Eng. T. !uthaaran

&!cEng. '/ip. (!tru. Eng), "%*E (!-)

Diploma Level


Construction Techniques 3+ercussion ,orin!

This method consists of breaing up the soil and roc formations by repeated blows of a chisel or bit,

suspended by a cable or rods ater should be added to the hole during boring and the pulveri7ed materials are bailed out at

intervals

This method is adopted for advancing a hole in all types of sub surface formations

!ince the materials are highly disturbed by the impact, the method is unsuitable for careful

investigations.

-v otar) %orin!

*n this system, boring is effected by the cutting action of a rotating bit which is ept in firm contact

with the bottom of the hole

/rilling mud is continuously forced down the hollow drill rods which collect the cuttings to the

surface. The method is nown as mud rotary drilling

ater is circulated down the hollow rods to facilitate cutting

Soil Samples

!oil samples are two types3 disturbed and undisturbed.

(i) /isturbed

" disturbed sample is that in which the natural structure of the soil gets partly or fully modified and

destroyed by the method of sampling. +atural water component may be preserved by suitable

precautions. The sample is suitable for mechanical analysis, determination of index properties, soil

classification and for carrying out compaction tests.

(ii) 8ndisturbed.

"n undisturbed sample is that in which the structure and properties of the material are preserved.

This may be obtained by careful protection and pacing and by the use of a correctly designed

sampler. Only undisturbed samples are suitable for tests on shear strength, consolidation and

permeability. These samples can also be used for other tests as for those of the disturbed samples.

,earin! capacit) o# oundations

"ny foundation should be designed so as to satisfy two essential re0uirements3

(i) *t must have a certain specified safety against ultimate failure.

(ii) The settlements under woring loads should not exceed the allowable limits for thesuperstructure in 0uestion.

2ltimate ,earin! Capacit)

*t is defined as the minimum gross pressure at the base of the foundation at which the soil mass fails

in shear

'ross pressure is the total pressure at the base of the foundation due to the weight of the

superstructure, self#weight of the foundation and the weight of earth fill, if any.

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Eng. T. !uthaaran&!cEng. '/ip. (!tru. Eng), "%*E (!-)

Diploma Level


Construction Techniques 3Sa#e ,earin! Capacit)

The safe bearing capacity is the ultimate bearing capacity divided by factor of safety.

actor o# sa#et)

The factor of safety to be selected depends on how accurately the soil conditions are nown, the type

of loading and the ha7ard imposed by a complete foundation failure.

$or most structures, where no possibility of soil failure can be tolerated and when there is a

reasonably accurate soil and loading information available, a safety factor of 2.: is employed.

*f there is a large component of live load that is liely to develop, a safety factor of 2 may be

employed.

hen the soil conditions are not well established, a factor of 4 should be used. $or temporary

structures.

here some ris of bearing failure can be tolerated a safety factor of .: may be used.

Soil Contamination

!oil contamination meas, the presence of man#made chemicals or other alteration in the natural soil

environment.

*t may occure due to

# 8nderground storage tans,# Oil and fuel dumping

# /irect discharge of industrial wastes

# "pplication ofpesticides.

There are three general approaches to clean up it# !oil can be excavated from the ground and be either treated or disposed

# !oil be left in the ground and treated in place or site# revent the contamination

'eneral rocedure

# ;eep a large plastic cover over the contaminated soil to prevent direct contract

# "llow rain water from seeping into the soil and spreading the contamination# Then flash the contaminants out of soil using water, hemical solvents or air

:
http://en.wikipedia.org/wiki/Underground_storage_tankhttp://en.wikipedia.org/wiki/Pesticidehttp://en.wikipedia.org/wiki/Underground_storage_tankhttp://en.wikipedia.org/wiki/Pesticide


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&!cEng. '/ip. (!tru. Eng), "%*E (!-)

Diploma Level



$.0 round WorksSite Works and Settin! *ut

The site having been taen over, the tas of preparing for and setting out the building can be

commenced. These operations can be grouped under three heading.i) learing the site

ii) !etting out the building.

iii) Establishing a datum level.

Site Clearin!

/emolition of existing building

'rubbing out of bushes and trees

1emoval of top soil because it is not good foundation of the building# 1emove 4cut? or >fill? or >cutting and fill? operation is needed

ut = is undisturbed soil for wor but costly

$ill = either deep foundation or large settlement to be accepted and not recommended for building

construction

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Eng. T. !uthaaran

&!cEng. '/ip. (!tru. Eng), "%*E (!-)

Diploma Level


Construction Techniques 3E'cavation Works

-i emoval o# Topsoil

The wor is being carried out in a redevelopment area, the first section of ground to be excavated is

the topsoil or vegetable soil

The reason for this is that the top layer of ground contains material which is decomposing along

with active plant life in the form of grass, flower, roots or shrubs, etc.

This material is easily compressible and as such n unsuitable for foundation

The topsoil layer approximately :< mm to 4


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Eng. T. !uthaaran

&!cEng. '/ip. (!tru. Eng), "%*E (!-)

Diploma Level


Construction Techniques 3educed Level E'cavation The ground which lies between the topsoil and the EarthBs crust is nown as the subsoil

*t comprises particles of weathered roc of various shapes and si7es

*t is usually necessary to provide a level surface from which construction may tae place

This level may be lower than the top of the subsoil

!o, it is re0uired to reduce the level of the ground

The volume of subsoil to be excavated, together with the nature of the material, will determine the

type of machine and method to be used.

,ulk E'cavation

*n this method large volume of subsoil are re0uired to be excavated in order to reach the formation

level

This type of excavation may be to reduce level or to provide basement areas

*n addition to the plant already mentioned, a face shovel may also be used for this type of wor

Trench E'cavation

+ormally after the formation of the level it will tae place, it is fre0uently necessary to excavate

trenches to a lower level

The foundation of the building are constructed in to the trench

!ome time trench may re0uired out side the building for the laying of pipes and cables which carrygas, water, electricity and other services.

*f the trenches are straight and uniformly shaped, it is generally cheaper to use a machine for the

excavation

*f the trenches are small and have a complicated layout, a gang of men with pics and spades can

still provide the most economical method of excavation

4ole or +it E'cavation

The design of the substructure may re0uired holes or pits to be excavated

*n the case of circular holes, hand or mechanically driven augers or drills can be used

its, being small shallow or rectangular holes, may be excavated mechanically or by hand.

Water in E'cavation

if excavation is to be carried out to a depth below that of the level of the water table, the excavated

area will be filed with water

*t is difficult to carry out further construction wor in water without incurring extra expense,

especially when wormen rather than machines are involved

The ground on either side of the excavated area is less stable and more liely to collapse when

waterlogged

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*t is therefore essential that any water which enter the excavation should be removed as soon as

possible or a better alternative is to prevent the water entering in the first place.


&!cEng. '/ip. (!tru. Eng), "%*E (!-)

Diploma Level


Construction Techniques 3round Water Control

ater from a particular area or merely to lower the water table to given reasonably dry woring

conditions especially for excavation activities

ater affects the stability and bearing capacity of a sub#soil

The effect of the water is that of a lubricant enabling them to move when subjected to a force such

as a foundation loading or simply causing them to flow by movement of ground water.

The voids caused by excavation wors encourage water to flow since the opposition to the ground

water movement provided by the soil has been removed.

*n cases where the flow of water is liely an artificial opposition must be installed or the lielihoodof water movement must be restricted by geotechnical processes.

These processes can be broadly classified into one two group.

i) ermanent exclusion of ground water.

ii) Temporary exclusion of ground water by lowering the water table.

+ermanent E'clusion o# round Water.

a Sheet pilin! 56

!uitable for all types of soils except boulder beds and is used to form a barrier or cut#off wall to the

flow of ground water.

The sheet piling can be of a permanent nature, being designed to act as a retaining wall or it can bea temporary enclosure to exaction wors in the form of a cofferdam

This method is unacceptable due to vibration and noise during the driving process

The capital costs can be high unless they can be apportioned over several contacts on a use and re#

use basis.

% Diaphra!m (alls 56

!uitable for all types of soils and are usually of in situ reinforced concrete installed using the

bentonite slurry method.

This form of diaphragm wall has the advantages of low installation noise and vibration, can be used

in restricted spaces and can be installed close to existing foundations.

'enerally, unless the diaphragm wall forms part of the permanent structure, this method is

uneconomic.

c Slurr) trench cut o## 56

These are non#structural thin cast in situ un#reinforced diaphragm wall suitable for sub#soils of silts

sands and gravels.

They can be used on sites where there is sufficient space to enclose the excavation area with a cut#

off wall of this nature sited

There is sufficient earth remaining between the wall and the excavation to given the screen or

diaphragm wall support.

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rovided ade0uate support is given these wall are rapidly installed and are cheaper than the

structural version.


&!cEng. '/ip. (!tru. Eng), "%*E (!-)

Diploma LevelEnvironmental Science and Construction Techniques 3

Construction Techniques 3d Thin !routed mem%rane 56

"lternative method to the slurry trench cut#off wall when used in silt and sand sub#soils, they are

also suitable for installation in very permeable soils and made up ground where bentonite methods

are unsuitable.

-ie the previous ample earth support is re0uired for this non#structural cut off wall.

The common method of formation is to drive into the ground a series of touching universal beam or

column sections, sheet pile sections or alternatively small steel box sections to the re0uired depth.

" grout injection pipe is fixed to the web or face of the section and this is connected, by means of aflexible pipe, to a grout pump at ground level.

"s the sections are withdrawn the void created is filled with cement grout to form the thin

membrane

e Conti!uous pilin! 56

"n alternative method to the reinforced concrete diaphragm wall consisting of a series of

interlocing reinforced concrete bored piles.

The formation of the bored piles can be carried out as ensuring that the piles interloc for their

entire length.

This will re0uire special cutting tools to form the ey in the alternate piles for the interlocing

intermediate piles. The pile diameter selected will be determined by the strength re0uired after completion of the

excavations to one side of the wall.

ontiguous piling can be faced with a reinforced rendering or covered with a mesh reinforcement

sprayed with concrete to give a smooth finish.

This latter process is called shot#rete or 'unite.

"n alternative method is cast in front of the contiguous piling a reinforced wall terminating in a

capping beam to the piles

Temporar) E'clusion o# round Water

a Sump +umpin! 56

!uitable for most sub#soils and in particular gravels and coarse sands when woring in open

shallow excavation.

The sump or water collection pit should be excavated below the formation level of the excavation

and preferably sited in a corner position to reduce to a minimum the soil movement due to

settlement which is a possibility with this method.

Open sump pumping is usually limited to a maximum depth of A.:< m due to the limitations of

suction lift of most pumps.

"n alternative method to the open sump pumping is the jetted sump which will achieve the same

objective and will also prevent the soil movement.


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*n this method a metal tube is jetted into the and the void created is filled with a sand media, a

disposable nose and strainer


Eng. T. !uthaaran

&!cEng. '/ip. (!tru. Eng), "%*E (!-)

Diploma Level


Construction Techniques 3% Well point s)stem 56

opular method of water lowering in non#cohesive soils up to a depth of between :.


12/30

"n alternative is the hori7ontal system of dewatering which consists of installing into the ground a


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*t will temporarily bloc off the face

The strut to be nailed or bolted to the ends tightly in order to avoid the falling

!teel trench sheets can be used instead of timber

/rive down the runners by a heavy maul

Tight the runners by using wedge against the face of excavation

hen the excavation reaches the level of the second bracing from the waling are threaded through

the struts of the top frame and then set in position


&!cEng. '/ip. (!tru. Eng), "%*E (!-)

Diploma Level



-onger uprights are set between the waling enabling the struts to be tightened against the face

uncheons are placed between waling to support the top frame

-acing boards are nailed vertically between pair of struts, it will brace the two frames together, so

uneven ground movement on either sides of the excavation and as safe guard to struts

*f the excavation is deeper set third frame

&ut usually runners are not more than 9.C m long

!econd and third settings need additional excavation.

Support %) sheet pilin!

!uitable for soft soil sub grade, can be used for compacted gravel ground or where soil containing

cobbles or boulders

+ormally can be used up to : m length

/riven by drop hammer or double acting hammer

The boulders to be remove before driving

reate noise and vibration

Tim%erin! (ith +olin! %oards

!uitable method for deep cuts in restricted site conditions

Example where width is not available for several setting of runners, or where little headroom is

available for pitching and driving sheet piling

The poling boards are 0uite short not usually more than .2 m with or without sharpened ends

itched out side timber guide the waling &y driving the boards in short stages immediately ahead of the excavation the ground is supported

all times

" tucing board will be placed in the space occupied by them before next setting of board is placed

"fter completion of driving a setting of boards the trucing board is replaced

4ori7ontal tim%erin!

!upport the ground by hori7ontal laggings between solider pile

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14/30

hen excavation is taen down timber laggings are inserted hori7ontally between the flanges of the

piles and held against the face by wedges

+ecessary to expose the ground over a depth of two or three boards to provide enough space to slip

one board between the flange

Support to sti#t cla)s compact or cohesive dr) sands or (eak rock strata

These materials can usually be relied upon to stand unsupported for a varying length of time

!upports are needed to prevent yielding and settlement of the adjacent ground surface and to ensurethe safety of wormen

'reatly simplifies procedure of timbering

/o the excavation up to the re0uired depth and place the boards


&!cEng. '/ip. (!tru. Eng), "%*E (!-)

Diploma Level



actors to %e considered (hen desi!nin! trench support

'round pressure of soils

"ngle of internal friction

Effect of water table

ressure from adjacent building

-oading caused by construction plant

What is #oundation&

*t is a sub structure transmitting all the loads to ground safely

Components o# oundations

+atural $oundation

"rtificial $oundation

Choice o# a oundation

"bility of artificial foundation to support the weight

"bility if the natural foundation to carry the loads

"bility of the structure to sustain small movement at foundation level

T)pe o# oundation

!trip foundation 3# $or low rise building

*solated foundation F ad foundation 3# !uitable for building having long span between the columns

and low stores building

1aft foundation 3# !uitable of medium rise building

ombination of all three above

ile foundation 3# !uitable for high rise building

Trench fill foundation 3# Guite small and no wider than the wall carried

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15/30

oundation t)pe availa%le in various t)pe o# soil

!and, gravel 3# ad foundation, !trip foundation and combined footing

%ade up ground 3# /raft foundation F ellular foundation

/eep clay F 8ncontrolled fill 3# ile foundation

unctions o# oundation

!afe load distribution 1esistance to settlement including differential

1esistance to shear

onsideration of seasonal movement


Eng. T. !uthaaran

&!cEng. '/ip. (!tru. Eng), "%*E (!-)



The #actors to %e considered (hen desi!nin! #oundation #or lo( rise %uildin!

'round bearing capacity

&ending and !hear

"cidity or "lalinity of soil

round "ovement

hange of soil particle level or location

hat are the factors

# !ubsidence due to mining underground

# Overloading of the natural foundation

# -owering of the ground water table# *ncrease in the water table level

# $ree7ing of moisture

# !ettlement

+recaution measure #or the sa#et)

"de0uate supply of timber or other suitable materials

Timbering should be carried out under supervisions of competent person %aterial used should be ade0uate strength

!ee 1esource %anagement note

:


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&!cEng. '/ip. (!tru. Eng), "%*E (!-)Diploma Level


Construction Techniques 33.0 Supper Structure

ramed ,uildin!

The purpose of any framed building is to transfers of the loads of structures plus any imposed loads

through the members of the frame to suitable foundation

$ramed buildings are practically suitable for

# %edium and high rise structures

# *ndustriali7ed low rise building $rames can be considered under three headings

lane frames

# $abricated in a flat plane

# 8sually called trusses or girders according to their elevation and shapes

# /esigned as a series of connected rigid triangle# %ainly used in roof construction and long span beam of light loading

!pace frame

# !imilar conception to a plan frame# /esign to span in two direction

# " series of lined yramid frames forming a light weight roof

!eleton $rames# !eries of rectangular frames placed at right angles to one an other# The loads are transmitted from member to member until they are transferred through the

foundation to the sub soil

# *t can be construct as followsi) oncrete seleton frames

ii) !teel seleton frames

iii) Timber seleton frame

$actors to be considered when selecting the material for frame structure

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# !ite condition

# Economics# "vailability of labours

# Time factors

# !tatutory regulation# apital costs

# ersonal preferences

unctions o# Skeleton #rame mem%ers%ain beam

!pan between the columns and transfer the live and imposed loads placed upon them to the columns

!econdary beam

!pan between the main beams

Transfer their loading to the main beams

1educe the span of the floors or roof being supported by the frame



Diploma Level


Construction Techniques 3Tie beam

&eams spanning between columns at right angle to the direction to main beams

!ame functions as main beams

*nternal beams

Edge beams

!ame as tie beams but spanning between external columns

olumns

ertical members

arry loads transferred by the beams to the foundation

$oundation

The base, to which the columns are connected

Transfer the loadings to a suitable load bearing subsoil

$loors

%ay or may not be an integral part of the frame

rovide the platform on which e0uipment can be placed and on which people can circulate

Transmitting these live loads to the supporting beams

1oof

!imilar to floors

%ain function is to provide a weather resistant covering to the upper most floor

Claddin!s8E'ternal Envelope to #ramed Structures

laddings are a form of masing or infilling a structural frame

A


18/30

rovides the resistance to the elements entry of day light, natural ventilation, fire resistance, thermal

insulation and sound insulation

*t can be consider under the following headings

i) !heet claddings

ii) &ric claddings

iii) *nfill panelsiv) urtain walling

v) oncrete claddings

"ll forms of cladding must fulfils the following functions

i) &e self supporting between the framing members

ii) rovide the necessary resistance to rain penetration

iii) &e capable of resisting both positive and negative wind pressures

iv) rovide the re0uired degree of thermal resistancev) rovide the necessary resistance to wind penetration

vi) rovide the re0uired degree of sound insulation to suit the building type

vii) 'ive re0uired degree of fire resistanceviii) rovide sufficient opening for natural day light and ventilation

ix) &e constructed to a suitable si7e



Diploma Level



) Sheet Claddin! -i! 9.:; 9.


19/30

# /urability is depend up on the alloy used

# /urability can be increased by painting

$. ,rick Claddin!s -i! lll.$


20/30

*nfill panels are light weight structures

'ive good internal natural day lighting

*t can be arranged to expose some or all of the structural members creating various optional

impression

Timber, steel, aluminium and plastic can be used

!ingle or double gla7ing techni0ues is possible

hen it is coated by dirt its visual appearance is less acceptable so need routine cleaning or

maintenance

>. Curtain Wallin!

*t is a form of external light weight cladding attached to a framed structure forming a complete

envelope or sheath around the structural frame

+on = loading bearing claddings

!upported only their own dead weight

ind load will be transferred to the structural frame through connectors usually positioned at floor

level

*t is a series of vertical mullions spanning from floor to floor interconnected by hori7ontal transoms

Opening into which can be fixed panels of glass or infill panels *t is a dry construction method, minimum load to structural frame

'ive good architectural feature


Eng. T. !uthaaran

&!cEng. '/ip. (!tru. Eng), "%*E (!-)

Diploma Level



Details o# rein#orced concrete cast in6situ (alls -i! lll.3; i! lll.@ i! lll.


21/30

# $orm si7es should be designed so that they are the maximum si7e which can easily be

handled by hand or by a mechanical lifting device# %aterial must be formwor units should be such that they can easily be assembled and

dismantled without any members being trapped

orm (ork materials

!oft wood boards

lywood

lipboard

!teel frame

"ould oils and Emulsions

&low holes, these are small holes being less than : mm in diameter caused by air being trapped

between the formwor and the concrete face

8neven colour, this is caused by irregular absorption of water from the wet concrete by the formwor

material

%ould oil can be applied to the inside surface of the formwor to alleviate these defects

To obtain smooth patterned or textured surfaces the inside of a form can be lined with various

materials such as oil tempered hardboard, mould rubber, mould and glass fiber and reinforcepolyester



Diploma Level


Construction Techniques 3T)pes o# #orm(ork

$oundation formwor

olumn formwor

&eam formwor

!lab formwor

all formwor

oundation #orm(ork -i! lll.10

$oundation may be any types

*f the subsoil is firm and hard it may be possible to excavate the trench or pit for the foundation to the

si7e and depth re0uired and cast the concrete against the excavated faces

*f this is not practicable formwor is needed

!ides and end anels will be re0uired

$irmly strutted against the excavated face

Ties will be re0uired across the top of the form as a top restraints and these can be utili7ed to form

the icer for a reinforced concrete columns

Columns orm(ork -i! lll.11 i! lll.13

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22/30

*t may be form or box consists of a vertical mould

The column box should be located against A: mm high plinth or icer which has been cost

monolithic with base or floor

Ti should be tight grout flow

hec and tie time to time

,eam orm(ork -i! lll.1=

*t consist three sides box hich is supported by cross member called head trees which are propped to the under side of the

soffit board

!offit board thicness is greater than the side boards

!offit board is inside of the beam side boards

Sla% orm(ork -i! lll.1?

$ormwor of floor or roof slab called as shuttering

+ormally consist of panels that can be easily handle

*t can be framed or joisted

an be supported by the beam forming with any intermediate propping -evel adjustment propping can be used





Wall orm(ork

There are two different way of formwors

Traditional formwor ($ig ll., $ig ll.2)

# The framed panels tied together over their bacs with hori7ontal members called waling

# *t will be formed above the A: mm height concrete icers# revent the loss of grout

# 8se pre#cast concrete spacer blocs to get the cover

# Timber or steel can be used

limbing formwor ($ig ll.4)

# same forms are used as in a repetitive fashion# %aximum usage of forms

# +eed minimum number of forms

# *t is possible to use this method for casting wall against an excavated or sheet piled bac face

using formwor to one side only by replacing

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"ethods o# Compactin! concrete

5and tamping

ibrating oer in concrete

4and tampin!

!uitable for small concrete wor and for testing (!lump, cube casting)

!i7e should be less than the spacing of reinforcement

Edge is rounded shape

9i%ratin! poker in concrete

oers are often used inefficient in site

$rom the observation of number of site about A< I of the operating time being made as waste

To get maximum use of poer and to give good compaction to concrete consider the following facts

# %ae sure you can see the concrete surface

# ut it in 0uicly, leave it in the concrete for about < seconds and with draw it slowly# ut the poer bac in not more than about :


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Warm Deck oo#

The insulation is placed above the roof dec but below the weather proofing

+o insulation below the dec and no ventilation is re0uired

External wall insulation needs to be extended up to the underside of the roof insulation to prevent

cold bridging

Cold Deck oo#

The insulation is placed between the flat roof joists at ceiling level

hen the insulation is placed at ceiling level there is possibility to form condensation so to prevent

it allow minimum of :< mm gap for ventilation above insulation

" vapour barrier should be placed on the warm side of the insulation

The roof to be ventilated by continuous gap running the full length of the eaves on two opposite

sides

The external wall insulation need to be extended up to the underside of the roof insulation to

prevent cold bridging

Cold deck #lat roo# Warm deck #lat roo#

1oof covering 1oof covering 1oof dec Overlay

entilated air space 1igid insulation

Thermal insulation apour control layer

apour control layer !tructural roof dec

eiling lining


&!cEng. '/ip. (!tru. Eng), "%*E (!-)

Diploma Level


Construction Techniques 3Concrete #lat roo# coverin!

1oof slab will be constructed as normal concrete reinforced concrete slab

$or small span timber roof is suitable, for a large span concrete flat roof can be used

1oofs are design to support the self weight of the roof together with loading from rain and snow

resist wind pressure and provide support for access for maintenance The concrete roof is supported on external walls with intermediate supports from internal loading

bearing walls or beams as necessary

The top of the flat roof will be sloped : J to < J to ensure the rain water flow

+ormally it will be done by a cement and sand screed with one way, two way or four way falls to

rain water outlets

2se o# ,itumen #elts coverin!

To prevent drying out of screed concrete in the top of the roof the bitumen felt covering is applied

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$elt roofs consist of two or three layers of sheet felt materials that form a dense, void less and

impermeable barrier

aterproofing agent such as tar or asphaltic bitumen that prevents ingress of moisture.

There are several ways of doing this

a. +our and roll5hot bitumen is poured in front of the felt as it is unrolled, and thus acts as the

adhesive and seals the laps.b. Torchin!5in this method specially designed felt is heated with a gas torch and no separate

bonding bitumen is needed. &est suited to repair wor, small areas, or where access to the roof

is difficult. The contractor must tae precautions against fire. Torching is not suitable over oradjacent to flammable materials.

c. Cold applied5here, a cold adhesive is spread onto the roof surface and the felts unrolled

into position. -aps are also sealed with the cold adhesive. Thus no bitumen boiler or gas torches

are re0uired, enhancing safety.d. Sel#6adhesive5 the undersides of these membranes include a high#tac adhesive and release

paper. Once positioned, the release paper is peeled off, and the membrane stuc down to the

substrate. They are not suitable for laying over uneven surfaces or in cold conditions. Theyre0uire rolling, or a soft broom applied over the whole area to assist full adhesion.

Sur#ace +rotection

"ll felt roofs need some protection. *f the only access onto the roof is for inspection, use either3

stone chippin!s(2Kmm)5these should be bonded to the waterproofing in a gritting compound, not

bitumen.

mineral #inish5small slate flaes are bonded to the felt during manufacture. arious colours are

available.

re#lective paints5although effective when first applied, these soon wear and discolour and need re#

painting every 4 to 9 years.

&itumini7ed roofing felt, unless carefully maintained, has a shorter life than other types of roof

covering and therefore, strict regulations control its use.


&!cEng. '/ip. (!tru. Eng), "%*E (!-)

Diploma Level



eneral

hen constructing of flat roofs consider the following

# %aterials used must be suitable for use in flat roofs# 1oofs need to achieve an external fire rating

# apour barriers should be used# $lat roofs should be anchored to walls to prevent uplift

# $lat roofs should be laid to falls# $lat roofs re0uire regular maintenance

+re6cast; +re stressed concrete section used as structural mem%ers #or #loor and #lat roo#s in skeletal

#ramed %uildin!

anel

lan

2:


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Trough

5ollow beam

!olid beam

* = beam

- = beam

T = beam

+ote3#. ommon forms of roof trusses and rafters = $ig ., $ig ll.99 L $ig ll.9:

2. Typical jointing techni0ues = $ig .2, $ig .4, $igll.96, $ig ll.9A, $ig l.: L $ig l.6)

# $or !teel 3# elding, &olted gusset plates to steel angle members# Timber 3# &olt or toothed timber connectors, nailed, glued plywood gusset plates


&!cEng. '/ip. (!tru. Eng), "%*E (!-)

Diploma Level


Construction Techniques 3E'ternal Work

Estate oads and +avement Construction

avement is a general term for any paved surface

*t is specifically applied to the whole construction of a road

*t can be classified as

(i) $lexible avements

(ii) $lexible avements

le'i%le +avements -i! 9ll.$ a

!ub base is laid directly onto the foundation

The formation level is nown as sub grade

*t is consist of well compacted granular material such as a 0uarry overburden or crushed rocs

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The thicness of sub base can be determined by using

# The cumulative number of standard axles to be carried and# &1 (alifornia &earing 1atio)

!e0uence of layer from bottom to top

# !ub grade

# !ub base# &earing course

# earing surface

sub base may be consist of any material which remains stable in water

*t is a relatively cheap flexible payment

i!id +avements -i! 9lll.$ %

*t is form of road using a concrete slab laid over a base layer

The preparation of the sub grade is as described above for above for flexible pavements

oncrete slab laid over the sub grade as sub base

Thicness is depend upon the nature and type of sub grade, intensity of traffic

1einforcement is provided to the slab accordingly

&efore the concrete is laid the base layer should be covered with a slip membrane of olythene

sheet to prevent the grout loss from the concrete slab

over of reinforcement depend on the thicness of concrete slab (but

normal range 9< M c M C


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The basic function of a retaining wall is to retain soil at a slope which greater than it would

naturally assume

*t is usually vertical or near vertical

+atural slope taen up by any soil is called its angle of repose

The wall are designed to offer the necessary resistance by using their own mass to resist the thrust

*t must be designed to ensure that

# Overturning does not occur

# !liding does not occur# The soil on which the wall rests is not overloaded

# The materials used in construction are not overstressed

$actors to be considered

# +ature and type of soil

# 5eight of water table

# !ub soil water movement# Type of wall

# %aterial used in the construction of the wall

Earth +ressure

"ctive soil pressure assive soil pressure

T)pes o# Walls

"ass retainin! (alls

!ome time called as gravity wall

1elying upon their own mass together with the friction on the underside of the base

'enerally economic up to a height of .C m

*t can be constructed by brics bedded in a 3 4 cement mortar or of mass concrete

+eed some light fabric reinforcement to control surface cracing

+atural stone is suitable for small walls up to .< m height


Eng. T. !uthaaran

&!cEng. '/ip. (!tru. Eng), "%*E (!-)

Diploma Level


Construction Techniques 3Cantilever etainin! (alls

1einforced concrete and wor on the principles of leverage

*t can formed with a large heel so that the mass of earth above can be added to the mass of the wall

for design O1

" large toe must be used

%ain reinforcement are in the tension face and minimum of reinforcement (


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1elying the depth of penetration in the soil

an anchored to ground

$or method see support to excavation

+re cast concrete retainin! (alls

re cast from high grade concrete with cantilever principle

an be erected on a foundation as a permanent retaining wall

" reduction in time by eliminating curing period and eliminating the need of costly form wor

&oth side reinforcement

-ifting holes are provided



Diploma Level


Construction Techniques 3=.0 nternal inishes

unction o# loor #inishes

+on slip

*mpact resistant

5ygienic

/urable

"coustic consideration

*mproved thermal insulation

2D


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unction o# Ceilin! inishes

"bsorption F reflection of light and sound

1esistance for flames

"esthetics

T)pe o# inishes

et $inishes = External wall

/ry $inishes = *nternal wall

unction o# e'ternal (all

Exclusion of wind F rain F snow

!olar reflection

thermal *nsulation

*mpact resistance

"esthetics

"aterial used #or (et inishes

!creeds

1enders

lasters boards

"aterials used #or dr) #inishes

laster board

all board

Tiles

lastic

lastic laminated sheets



Documents

Construction Techniques - 3