FRAMED- TRUSS SYSTEMS FOR LARGE SPAN INDUSTRIAL …

FRAMED- TRUSS SYSTEMS FOR LARGE SPAN INDUSTRIAL STRUCTURES

A DISSERTATION Submitted in partial fylfiliment of the

requirements for the award of the degree ©f

MASTER OF TECHNOLOGY in

CIVIL ENGINEERING (p ith Specialization yin Structural Engineering)

By

MAHESH GAMI

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Date I ?th....

DEPARTMENT OF CIVIL ENGINEERING INDIAN, INSTITUTE OF TECHNOLOGY ROORKEE

ROORKEE - 247 667 '(INDIA) JULY, 2012

CANDIDATE'S DECLARATION

I hereby declare that the work which is being presented in this dissertation entitled

FRAMED-TRUSS SYSTEMS FOR LARGE SPAN INDUSTRIAL STRUCTURES, in

partial fulfillment of the requirements for the award of the degree of Master of Technology

in Civil Engineering with specialization in Structural Engineering submitted in the

Department of Civil Engineering, Indian Institute of Technology Roorkee, Roorkee, is an

authentic record of my own work carried out for a period from July 2010 to June, 2012

under the supervision of Dr. J. Prasad, Associate Professor and Dr. Bhupindar singh,

Associate Professor, Department of Civil Engineering, Indian Institute of Technology

Roorkee, Roorkee.

The matter embodied in this dissertation has not been submitted by me for the award

of any other Degree.

Date: July 04, 2012

(Mahesh Gami)

Place:IIT Roorkee

CERTIFICATE

This is to certify that the above statement made by the candidate is correct to the best of my

knowledge.

JA ~~ 1)r. BhupIkdar Singh

Dr. Jag rasad

Associate Professor, Associate Professor,

Department of Civil Engineering Department of Civil Engineering

IIT Roorkee, IIT Roorkee,

ACKNOWLEDGEMENT

I wish to express my deep sense of gratitude and sincere indebtedness to my

guides, Dr.Jagadish Prasad, Associate Professor, and Dr. Bhupindar Singh, Associate

Professor, Department of Civil Engineering, Indian Institute of Technology Roorkee for

their kind cooperation and encouragement that they have given me to bud new ideas in

tackling the various situations while doing the dissertation work. Their undying

determination to get the best out of their students served as inspiration for completion of

this report. Their unique way of explaining things using examples related to day to day

life are truly praiseworthy.

I am also grateful to my friends and Family who actively got involved in providing me

with vital support and encouragement whenever I needed.

MAHESH GAMI

ABSTRACT

Large span (30-60m) Industrial Roofing systems have traditionally been done

through conventional simply supported Truss systems using open sections such as Angle,

Channel and I-section. This needs a large height for the truss system so as to create high

moment resisting capacity by members which are capable of carrying axial forces only.

The large space between the bottom chord and the ridge remains unutilized (5-7m height)

and provides a very large projected area for the wind pressure to act. As a consequence to

this, the truss spacing is reduced so as to deal with comparatively low values of load. Use

of closed form tubular sections has helped in meeting some requirements up to some

span. In the recent time, however, framed truss made in high strength steel (300-35OMPa

as against 250 for hot rolled section) hollow sections has become quite popular. The roof

slop of the framed truss is generally in the range of 5°-7° as against l00-150 for

conventional trusses. The roofing system of an industrial building comprises elements

such as Purlins and roof sheeting. All these elements transfer the imposed loads through

flexural actions to rafter of framed truss. To deal with large moment on account of very

large spans with force couple action large liver arm (truss depth) is required. Also, the

moment in the rafter of the frame varies in a parabolic profile with respect to span and

hence a constant truss depth becomes inefficient in comparison with trapezoidal shaped

framed truss. This type of manufacturing has now become feasible and cost-effective.

This category of work in steel is referred to as Pre-Engineered Building (PEB).

In the present thesis work, framed truss have been studied for their performance

for the span of 30 and 40m. The rafter inclination has been kept in the low range of 5°-7°

with a column height of 6m and frame spacing about 5-6m. The elements of rafter such

as Eva depth, ridge depth, and number of panels for various web patterns have been

varied in the suitable range to study their impact/influence on the ridge deflection and

finally the percent capacity utilization of various members. The results have been

presented in a lucid manner in a combination of graphical and tabular form.

Contents

CHAPTER PAGE

ACKNOWLEDGEMENT ------ II

ABSTRACT ------ III

FIGURES ------ VI

TABLES ------ VII

NOMENCLATURE ------ VIII

NOTATIONS ------ IX

1. INTRODUCTION

1.1 General ----- 01 1.2 Breif Review of Assosiated Literature ----- 04 1.3 Critical Coments 05 1.4 Problem definition ----- 05

1.5 Scope of work ----- 05

1.6 Organisation of thesis. ----- 06

2. REVIEW OF LITERATURE

2.1 General ------ 07

2.1.1 Hollow sections ------ 07 2.1.2 Cold Formed steel ------ 08

2.2 Literature review on Cold-formed Steel sections ------ 11

2.3 Literature review on Tubular trusses ------ 12 2.4 Critical coments ------ 13 2.5 Justification of the problem ------ 13

3. THEORITICAL PART

3.1 General ------ 14

3.2 Selection of member cross-section ------ 14 3.3 Frrned-truss system ------ 15

3.4 Design criteria

3.4.1 Behaviour of light gauge sections ------ 15

3.4.2 Effective design width of stiffed elements ------ 18 3.4.3 Tension member ------ 19

LP/

3.4.4 Compression --- --- 20

3.5 Relative Merites of tubular sections --- --- 22

3.6 Deflection Criteria --- --- 25

4. PROBLEM UNDER STUDY

4.1 Common Data --- --- 26

4.2 Materials used and their properties --- --- 26

4.3 Detail explination of the problem considered --- --- 26

4.4 Analysis --- --- 29

4.5 Sequence of the study --- --- 30

5. RESULTS 5.1 Results for 30m span

5.1.1 Effect of increasing Eva & Ridge depth --- --- 32

5.1.2 Effect of Roof angle --- --- 36

5.1.3 Effect of number of panels --- --- 37

5.2 Results for 40m span

5.2.1 Effect of increasing Eva & Ridge depth --- --- 41

5.2.2 Effect of Roof angle --- --- 45

5.2.3 Effect of number of panels --- --- 46

5.3 Design of typical Framed Truss --- --- 50

5.3.1 Design of typical framed truss for 30m span --- --- 53

5.3.2 Design of typical framed truss for 40m span --- --- 56

6. DISCUSSION AND CONCLUSIONS

6.1 Aim of study ---- -- 59

6.2 Discussion and conclusions ---- -- 59

6.3 Scope for futer study ---- -- 61

REFERENCES ------ 62

LIST OF FIGURES

Title Figure .No Page

Typical Pre-engineered building 1.1 3

Various terminologies used for Framed-Truss 1.2 3

Nature of axial forces in Framed-truss members-

-for gravity loading, with different web patterns 3.1 16

Buckling coefficients for flat rectangular plates 3.2 17

Effect of increasing depth at Eave and Ridge For 30m span for 5° , 6° & 7° roof angles -------- 32 to 35

Effect of roof angles (span: 30m) 5.1.6 36

Effect of number of panels for 30m span for various web patterns -------- 37 to 40

Effect of increasing depth at Eave and Ridge For 40m span for 5°, 6° & 7° roof angles -------- 41 to 44

Effect of roof angles (span: 40m) 5.2.6 45

Effect of number of panels for 40m span For various web patterns -------- 46 to 49

Stress ratio for truss members (span: 30m) -------- 53 to 55

Stress ratio for truss members (span: 30m) -------- 56 to 58

Photos regarding Pre-engineered Buildings, - -------- Appendix-A Manufacturing of hollow sections and their- Connections.

LIST OF TABLES

Title Table .No

Cold rolled versus Hot rolled ---

Chronicle summary of cold-formed-

-steel framing standards ----

Values of `k' for various stresses under-

-different boundary conditions ----

Effective length of prismatic member ---_

Deflection Limits ----

Varying range of various parameters -

For the study purpose ----

Properties of square Hollow-sections ----

F ramed-truss system design data (span: 30m)

Design cross-sections and corresponding-

-frame deflection (30m)

Framed-truss system design data (span: 40m)

Design cross-sections and corresponding-.

-frame deflection (40m)

2.1

2.2

3.1 ----- 18

3.2 ----- 21

3.3 ----- 25

4.1 ------- 27

4.2 ------- 28

5.3.1 - ------ 53

5.3.2 ------- 54

5.3.3 ------- 56

5.3.4 -- 57

NOMENCLATURE

YS _ Material yield strength

E - Modulus of elasticity of steel

- Poisson's Ratio

- Deflection of plate perpendicular to surface

w - Width of plate

a - length of plate

d - Depth

t - Thickness

k - Buckling coefficients

A - Area of the cross-section

D - Deflection

W - Weight

A„et - net cross-sectional area

L r, - effective length

- slenderness ratio

cyst - permissible stress in axial tension

Qac - allowable compressive stress

6cr - critical buckling stress

f - elastic critical stress

p - Unit mass of steel

'-'max _ Maximum allowable deflection

nr - Deflection ratio

A - Actual Deflection

i

VIII

NOTATIONS

Abbreviations

PEB - Pre-Engineered Building

FT - Framed-Truss

SHS - Square-Hollow section

RI-IS - Rectangular-Hollow section

CTS - Cylindrical Tubular section

IX

CHAPTER 1 INTRODUCTION

1.1 General:

The trusses are vector active structural system made up of short and straight lineal

members, in which redirection of forces is effected by vector partition, i.e. by

multidirectional splitting of single force simply to tension or compressive elements. As in

trusses moment is resist by forming force couple. In the simply supported structure the

maximum moment is produced in the middle of span. For the long span simply supported

trusses demand large depth in the middle span to have larger liver arm, due to which the

depth of truss is becomes nearly equal to height of column, which result in higher wind

load and uneconomical structure.

In recent years, framed truss with tubular members have provided practical and

economical design solutions for warehouses, Storage sheds, various factory buildings and

for other civil/military purposes particularly in the span above 30m. The name framed

truss indicates the 'truss is connected with column/s at two vertically separated points i.e.

at top and bottom chord level by pin connection. Due to which the central moment of

simply supported truss is distributed between support and midpoint of span which result

in requirement of small and uniform depth of truss. Both top and bottom chord of framed

truss are sloping and this slope increases the stability and reduces the deflection. The

main advantages of a framed truss are

a) Larger spans possible.

b) Clear height available within the framed structure is more than available in

conventional simply supported truss.

c) Less depth of truss require for given span compared to Simply support truss.

d) Lighter construction for same span when compared to conventional simply

supported truss.

e) It has advantages of both Gable frame and truss system.

f) This configuration reduces the problems associated with the chord members adjacent to the supports in simply support truss.

The most common form of framed truss is the pinned-base framed truss with

different rafter and columns (framing elements), shapes and sizes. These framed trusses

form the primary framing structure of a pre-engineered building which are the main load

1

carrying and support members of the buildings. In pre-engineered buildings, the ec

trusses usually formed by welding together steel tubular members of higher strengt

form the truss panels. The panels of suitable sizes are then field-assembled (e.g. bo ete

connections or welded connections) to form the entire framed truss of the pre-engineerec

building.

Most of the times, the rafter and columns (framing elements, Fig: 1.1) are tapered

(varying in depth) according to the local loading effects. Tapered elements are widely

used in steel framed truss to make the stress in the structure more evenly distributing, so

that the consumption of steel can be reduced this is done because of the non-uniform

distribution of bending moments.

Use of hollow sections, has been growing in popularity over the years. Now that

fabrication by welding has become normal connection/joining practice, and in certain

cases preferable to bolted structures. (Riveting having become almost obsolete), it has

automatically followed that use of tubular structure should have received the attention of

structural engineers. More so, because, they are predominantly welded structures, except

where bolts are used for erection purpose, or for joining at site of individual pre-

fabricated components.

There are several reasons which have led to the increase use of tubes, and one of

the most significant is the excellence mechanical properties of tubular members.

Structural hollow sections have high bending and Torsional rigidity compared to their

weight and they are suitable for compressed members. Another reason that can be

mentioned is the large amount of research which has been done to ensure the safety of the

design codes of tubular members and joints. Also the selection of commercially available

tubular profiles is large which makes it possible to choose appropriate profiles in a truss.

Cold formed Z and C-shaped members may be used as secondary structural

elements such as purlins, girts to fasten and support the external cladding. The connection

of purlins with the roof cladding and girts with wall cladding is more effective using the

self tapping screws all along the length of the purlins and girts. A picture showing a

connection of a purlin with the roof sheeting using a self tapping screw is available in

Appendix —A. Cold-formed steel products are made by bending a flat sheet of steel at

room temperature into a shape that will support more load than the flat sheet itself. They

nuo:us bearr rind

a Post and beam heig endframe

Ainchor .-.-s jj indpost

ep

Eave

Eave

Truss Height

Roof Angle

Eave pur n

RI

abIe wall

Fig: 1.1, Typical Pre-Engineered Building

Top Chord Bottom Chord

Eave Depth

Eave Height

Column Truss

Hinge Support

Ridge Depth Vertical Web member

Truss Panel

Rif Truss Truss Height

Inclined Web member € oof Angle

CIearSpan --

Column Truss

Span

Hinge Support

Fig: 1.2, Various terminology used for Framed Truss

have been produced for more than a century since the first flat sheets of steep were .

produced by the steel mills. However, it is only in recent years that higher stren ,

materials and a wide range of structural shapes and sizes have caused a significant growth

in cold-formed steel relative to the traditional heavier hot-rolled steel structural

members.

The designing of Pre-Engineered Buildings (PEB) is quick and efficient as they

are made of standard connections and sections. In contrast to PEB's conventional steel

buildings require enormous labor and heavy equipments. Future changes can be more

easily incorporated in PEB's as compared to conventional. Some of the figures to get an

idea regarding the Pre Engineered Buildings and the various connections of different

elements is listed in Appendix-A.

1.2 BRIEF REVIEW OF ASSOCIATED LITERATURE

J. Marshall (1972), studied Torsional behavior of structural rectangular hollow

sections. This paper presents a basis for determining displacements and stresses arising

from the torsion of structural rectangular hollow sections. Jeffrey A. packer et al. (1986)

Design aids and design procedure for HSS trusses. In implementing the IIW

recommendations, some conservative modifications needed to be made, and resistance

factors were also derived from an extensive international data base. Some more

researchers are focused their investigation on rectangular hollow section joints, and other

focused on optimization of tubular tresses using Heuristic Algorithms (Jussi Jalkanen,

2007). Zhi-ming Ye , Roger Kettle and Long-yuan Li (2004), carried out a analytical

study on a model for cold-formed purlin-sheeting systems subjected to wind uplift

loading in which the restraint of the sheeting to the purlin is taken into account by using

two springs representing the translational and rotational restraints provided by the

sheeting.

Cold-formed steel products are made by bending a flat sheet of steel at room

temperature into a shape that will support more load than the flat sheet itself. However, it

is only in recent years that higher strength materials and a wide range of structural shapes

and sizes have caused a significant growth in cold-formed steel relative to the traditional

heavier hot-rolled steel structural members.

4

The Design Standard for hot-rolled steel is developed by American institute of

Steel Construction (AISC). Certain Guidelines for design of a steel building have b

made by AISI, but there exists limited laid down methodology for use of Indian Codes for

design of a steel truss or any other structure.

1.3 CRITICAL COMMENTS

From all the research papers that has been reviewed so far it is noted that a good

amount of research has been carried out in different aspects of strength and stability of

conventional truss with tubular section and also in Cold-formed steel sections.

But there exist limited guidelines or standard methodology for design of a framed

truss. The process is complicated since tools for analysis of a framed truss with tapered

shape are not easily available to lay engineers.

1.4 PROBLEM DEFINITION

An internal framed truss with hinge support of an Industrial building of two

different spans viz., 30m and 40m is considered for the present study. For the purpose of

study the loading on the frame is taken as lOkN/m along the top chord. The column

height has been taken at 6m in all the cases. The aim of the study is to have some

preliminary design considerations in fixing up the roof truss geometrical dimensions

which gives a shape which is structurally efficient in terms of controlling the deflection

and proper utilization of steel. Efforts have been made to vary all the relevant geometric

parameters (including roof angle), rafter web pattern and number of panels in a realistic

range and their effect on ridge deflection and weight of rafter of framed truss is observed.

In addition to this, final typical design is performed with keeping in mind the availability

of steel tubular sections of various cross-sections.

1.5 SCOPE OF WORK

Analysis of a framed truss to arrive at values of maximum deflection at ridge

point, utility ratio of truss members and weight of the structure has been carried out using

STAAD-Pro 2007.

The values so obtained will be plotted against, rafter depths variation at Eva and

ridge level, roof angle variation and variation in number of panels so as to provide a

5

preliminary guidelines for selection of Initial shape and topology by a s ruc urai designer.

while designing a framed truss for large span industrial buildings.

1.6 ORGANIZATION OF THESIS

The Thesis is divided into six chapters. Chapter 2 consists of Review of literature.

Chapter 3 discusses Theory related to Design of a Framed-truss, Steel Design and

properties of materials, namely steel that is being utilized. Chapter 4 gives the clear

picture of the Problem under study in detail Chapter 5 consists of presentation of results

so obtained and deriving a correlation from the corresponding Chapter 6 the final

discussions and conclusions are given.

CHAPTER 2 LITERATURE REVIEW

2.1 General: .

Literature survey is essential to review the work done in the area of related

engineering field. Taking care the specific needs of closed form section properties and its

behaviour for the understanding of design, the literature like technical papers, journals

and books need to be referred. The prime importance in the review was to understand the

structural behavior of Tubular sections, cold formed steel and truss structure.

2.1.1 Hollow Steel Sections:

The increasing use of tubes, as a consequence, has made it necessary upon various

international standards institutions to pay adequate attention to control quality,

permissible stresses, welding procedures etc., for such structures, several standards have

come up in Britain, America, Europe and even in India to regularize procedures aiming at

ensuring quality and procedures of designs which can be expected to meet the

requirements of different civic or private bodies, and Government agencies. BS: 5950

part-I — "The use of structural steel in Building design" and its Indian counterpart IS: 800

and BS:1387- "Steel tubes and tubulars" as also similar other European and Americans

codes cater to the standardizations of material, stresses, and other requirements in general.

Material and dimensional specifications for tubes in India conform to IS: 1161, IS: 806

(Use of Steel Tubes in general building construction), and IS: 1293. Engineering today,

besides using tubular circular enclosed sections are also showing advantages for ready-

made rectangular or square hollow sections conforming to IS: 4293. Apart from average

material savings, which is quite significant, these sections have other positive attributes,

such as lower wind drag coefficient, lesser corrosion and improved aesthetic appeal.

Closed structural sections (RHS/SHS/CTS) have many advantages over

Conventional structural sections

➢ The excellent distribution of the materials around the axes of closed structural

exhibit remarkable strength qualities and thus offer decisive advantages as regards

to application technology.

7

➢ Due to their high torsional rigidity and compressive strength, closed structural

members behave more efficiently than conventional structural members.

➢ The smooth uniform profile of these sections minimizes corrosion and facilitates

ease, at site fabrication.

➢ Such sections have a higher resistance to bending in torsion also they show a

marked superiority over conventionallunconventional open sections such as

channels, angles, etc.

➢ Such sections have a smaller slenderness ratio on weight to weight basis than

conventional sections. Thus they can be designed for higher stresses.

➢ RHS have greater shear strength due to double web. They are light to handle,

allow easy shop fabrication and quick and economic erection.

➢ Since. RHS/SHS have flat sides, fabrication can use existing equipment designed

for fabrication with conventional sections.

➢ Special profiling, cutting (i.e. edge preparation) and welding technique, usually

associated with tubular fabrication are not required. Joints are generally less

complicated than joints with conventional sections.

➢ RHS/SHS structures are cleaner, as there is little room for formation of dust traps.

➢ Painting cost is less as the painting surface of RHS/SHS is about 20% to 30% less

than other conventional sections.

➢ Although, RHS (Rectangle Hollow Sections) and SHS (Square Hollow Sections)

are slightly more expensive as compared to conventional sections, the high

strength to weight ratio ensures a considerable weight saving, when incorporated

in an efficient design. This reduces foundation, handling, erection and

transportation costs.

2.1.2 Cold-formed steel:

Cold-formed steel products are made by bending a flat sheet of steel at room

temperature into a shape that will support more load than the flat sheet itself However, it

is only in recent years that higher strength materials and a wide range of structural shapes

and sizes have caused a significant growth in cold-formed steel relative to the traditional

heavier hot-rolled steel structural members. The advantages of cold formed over hot

rolled sections are listed in table 2.1 below.

Hot Rolled Cold Rolled

Material Yielding The material is not deformed; The yield value is increased by Properties Strength there is no initial strain in the 15%-30% due to prework (initial

material, hence yielding starts deformation). at actual yield value as the original material.

Unit Unit weight is comparatively It is much smaller. Weight huge.

Ductility More ductile in nature. Less ductile.

Design Most of the time, we consider Local buckling, Distortional only the global buckling of the Buckling, Global Buckling have to member. be considered.

Flexibility Standard shapes are followed. Any desired shape can be molded of Shapes High value of unit weight limits out of the sheets. The light weight

the flexibility of manufacturing enhances its variety of usage. wide variety of shapes.

Economy High Unit weight increases the Low unit weight reduces the cost overall cost — material, lifting, comparatively. Ease of transporting, etc. It is difficult construction (e.g. connection). to work with (e.g. connection).

Research In the advanced stages at More possibilities as the concept is Possibilitie present. relatively new and material finds

s wide variety of applications.

Table: 2.1, Cold rolled versus Hot rolled

E

Cold-formed sections, being thinner than hot-rolled sections, have different

behavior and different modes of failure. Thin-walled sections are characterized by local

instabilities that do not essentially lead to ultimate failure, but are helped by post buckling

strength, hot-rolled sections rarely exhibit local buckling. The properties of cold-formed

steel are altered by the forming process and the residual stresses are significantly

different from hot-rolled.

The industry of cold-formed steel differs from hot-rolled steel in an important way:

there is much less standardization of shapes in cold-formed in relation to hot-rolled steel.

Rolling heavy structural sections involves a major investment in machine and equipment.

The handling of heavy billets, the need to reheat to 2300°F, the heavy rolling stands

capable of exerting great pressure on the billet, and the loading, stacking, and storage of

the finished product all make the production of hot-rolled steel shapes a significant

financial investment by the manufacturer. Conversely, all it takes to make a cold-formed

structural shape is to take a flat sheet at room temperature and bend it. The equipment

investment is much less than that for hot-rolled industry and the end product coming out

of the last roller stand can often be lifted by one person. Therefore, from these aspects it

may be inferred that there is need to have a different design standard for cold-formed

steel structures. Some design codes developed for cold-formed steel framing is given

below in table 2.2.

Year Published Significances

1996 The first edition of the combined ASD and LRFD Specification

was published.

1996 The first edition of the Prescriptive Method for Residential Cold-

Formed Steel Framing was published and was adopted by IRC

2000.

2001 The following standards were first published:

1) Standard for Cold-Formed Steel Framing -Prescriptive

Method for One and Two Family Dwellings

2) Standard for Cold-Formed Steel Framing -General

Provisions

3) Standard for Cold-Formed Steel Framing -Truss Design

10

4) Standard for Cold-Formed Steel Framing - Header Design

2004 The following standards were first published:

1) Standard for Cold-Formed Steel Framing -Lateral Design

2) Standard for Cold-Formed Steel Framing -Wall Stud

Design

Table: 2.2 Chronicle summary of cold-formed steel framing standards

2.2.1 Some literature regarding cold formed-steel section:

(Ghosn and Sinno, 1995), have shown that the most common failure of the lapped

connections over the internal supports of multi-span purlins is mainly caused by the local

buckling of the compression flange, and the key parameter controlling the load carrying

capacity of the lapped connection multi-span purlins is the moment resistance.

(Zhi-ming Ye et al. 2004), carried out a analytical study on a model for cold-formed

purlin-sheeting systems subjected to wind uplift loading in which the restraint of the

sheeting to the purlin is taken into account by using two springs representing the

translational and rotational restraints provided by the sheeting. The results obtained from

this study not only highlight the influence of the sheeting restraints on the results of

stresses but also can be used as an input to the finite strip code for carrying out the linear

elastic buckling analysis of the sections. The two springs have different influence on the

buckling behavior of the purlin. The translational spring has more influence on the local

buckling while the rotational spring has more influence on the lateral torsion buckling.

For the distortional buckling, the influence of the two springs is mixed and is interfered

by the loading position.

(Ho and Chung, 2004), have provided experimental evidence for semi-continuity of

lapped purlins and shown that it depends not only on the stress level and the connection

configuration (e.g. location of bolts on web or on web and flanges) but also on the lap

length-to-section depth ratios. They have also shown that the failure mode of such purlins

is mostly influenced by the shear buckling of the web of single sections at the edge of the

lapped length and, consequently, the design procedure must include checking against

combined bending and shear in this point.

11

(Zhang and Tong, 2008), concluded that the edge section of lapped connection is the

most critical. Because the moment resistance of built-up lapped sections on the internal

support is almost twice the one of single sections at the edge of the lap, it implies that

only this one needs to be checked for strength. - the failure of such purlins usually occurs

at the edge of the lap zone by the local buckling of compression flange; _ additionally, the

failure of purlins is influenced by the shear buckling of the web of single section at the

edge of the lap.

2.2.2 Some literature review on tubular trusses:

Many studies have examined the structural behavior of tubular members in the

past several decades. Some of them have been listed over here.

(Jeffrey A. packer et al. 1986), "Design aids and design procedure for HSS trusses". By

using these design aids, one gains an appreciation of the principal parameters affecting

the strength of a truss joint and thereby selects truss members in, a more efficient manner.

Also there are design examples given by the writers for further clarification and

assistance. In this paper separate design procedures are given for gapped and overlapped

joints types, for most failure modes, the joints adequacy should be checked for both the

compression web critical and tension web critical cases.

(Wei-wen yu, 1979), "Cylindrical Tubular Members". Book of cold form steel structures

design, analysis and construction. Discuss various types of steel tubes grouped as

manufactured tubes and fabricated tubes. Explain various buckling problem associates,

local buckling, elastic buckling and inelastic buckling with example. Various design

criteria as per AISI Specification and CRC formulae are considered.

(J. Marshall, 1972), "Torsional behavior of structural rectangular hollow sections". This

paper presents a basis for determining displacements and stresses arising from the torsion

of structural rectangular hollow sections. Particular attention is given to stress

concentrations at the re-entrant corners. A relationship is determined between freely

formed corner redial and section thickness. Analytical solution is compared with

experimental results on steel sections and predictions from thin walled torsion theory. The

first part of this paper is concerned with giving a general procedure for determining stress

concentration factors within the range of structural rectangular hollow sections and which

takes account of the radius at an external corners.

12

(J. Wardenier, 2002), "Hollow sections In Structural Applications". The author has had

an enormous impact on the design methods for tubular steel structures in the late 20 n

century. This book cover all aspect related to design of tubular structural members and

different type of connections.

2.3 Critical comments: ♦ From all the research papers that has been reviewed so far it is noted that a

good amount of research has been carried out in different aspects of strength

and stability of tubular structural members such as local and lateral buckling

effects, flexural or Torsional buckling effects, various connections in tubular

structures, and also on post buckling effects in cold-formed steel sections has

been done so far.

♦ So, in the present report, study has been carried out to come up with some

preliminary design considerations of a framed truss with respect to roof angle

variation & optimum depth for roof truss at eave and ridge level which give an

efficient and economical framed truss under vertical loading.

♦ There is a limitation in selection of preliminary geometry of rafters and the

columns. So, efforts are needed to study the effect of different aspects such as

shape and topology of rafter & columns on stability (deflection) and utility

ratio to come up with a structurally efficient and safer framed truss.

2.4 JUSTIFICATION OF THE PROBLEM UNDER STUDY:

In the present report, efforts have been made to observe the effect of variation of

geometric parameter of rafter element in a suitable range on ridge deflection, stress utility

fectore of truss members and finally on the weight of the truss and come up with some

guidelines that enables an engineer in selection of preliminary shape of a rafter for large

span industrial buildings.

13

CHAPTER3 THEORETICAL PART

3.1 General

Steel, as a construction material displays high values of yield stress, while

compression it generally fails in local or shear buckling. A large number of studies have

been conducted considering the various elements to behave as plates with varying support

conditions as per their location. In modern day practices, where Pre-Engineered steel

sections are the norm of the day, due to the thin sections employed, local buckling

becomes a major design criteria, As studies in steel buckling show, failure occurs at

generally 2-3.5 times the theoretical buckling load. This gives rise to the present

condition where post-buckling strength of a section is utilized in design.

The truss is framework in which the members are connected at their ends. To cover a

certain area a series of trusses are placed on wall or two parallel lines of columns. The

trusses support the purlins on their principal rafters and the purlins support the roof

covering either directly or through common rafters and battens.

3.2 Selection of the member cross-sections

For optimization of the truss weight, the member shape plays major role, because

for design of compression member, the radius of gyration comes in picture, which

depends on the member shape. For any compression member, the higher radius of

gyration gives lower slenderness ratio and ultimately gives higher permissible

compressive stress value, which leads to lighter sections for given loading.

The closed structural sections (RHS/SHS/CTS) have higher radius of gyration compared

to the other conventional sections i.e., Angle sections, Channel sections, I-Sections etc.

Closed structural sections (RHS/SHS/CTS) have many advantages over Conventional

structural sections,

➢ The excellent distribution of the materials around the axis of closed structural

exhibit remarkable strength qualities and thus offer advantages as regards to

application technology.

➢ Due to their high torsional rigidity and compressive strength, closed structural

members behave more efficiently than conventional structural members.

14

➢ Their higher strength to weight ratio results in up to 25 % saving in steel.

➢ The smooth uniform profile of these sections minimizes corrosion and facilitates

ease, at site fabrication.

➢ Closed structural members also enhance the aesthetic appeal of structures.

3.3 Framed truss system

In case of very long span length Framed truss having trapezoidal configuration,

with depth at the ends and have hinge-connections at two vertically separated nodes/joints

along the height of the column/s are used. This configuration results in shifting of the

moment resisting capacity of the truss from central/mid-span section to the support point

section.

The trapezoidal configurations having the sloping bottom chord can be economical in

very long span trusses (spans > 30 m), since they tend to reduce the web member length

and the chord members tend to have nearly constant forces over the span length. It makes

available higher room-space near the central part of the covered area.

3.4 Design Criteria

The truss members e.g. top & bottom chord members, vertical web members and

inclined web members which are subjected to axial tension and compression, various

design criteria associated with design are discussed below.

3.4.1 Behavior of Light-Gauge Sections [IS 801: 1975]

The element of light-gauge section is subjected to local/plate buckling. The thin

elements are subjected to compressive stresses when the sections are used as the

compression members or flexural members. The thin elements act as plates and are

susceptible to buckling known as local or plate buckling. This type of buckling may be

prevented by providing a minimum thickness to the elements of the section. The critical

buckling stress air for a rectangular plate supported on all edges is iven by

6cr — k1T2 E

12(1 — v2)(b/ ACCNo..... 75 . ~...rp

\ ti

Date. •i.? .)0 )-2-- ,•

ROOS'~"1t

Red:- Compression

Blue: - Tension

Fig:- 3.1, Nature of axial forces in Framed-truss members for gravity loading, with

different web pattern

16

Where, k=[M(W)+

z

1 a a mw

E = Modulus of elasticity of steel, 2x105N/mm2

t = Thickness of Plate

v = Poisson's Ratio= 0.3 for steel in elastic Range

w = Width of plate

a = length of plate

: JfiE

Fig:- 3.2, Buckling coefficients for flat rectangular plates

The value of `k' is thereafter derived for varying values of m'. The values are as shown

in above.

If all the edges are simply supported = 4.0.If one of the edges parallel to the loading is

free, the value of k reduces drastically to 0.425. The additional values of `k' are as

provided in the table 3.1.

Hence, the element of a light-gauge section with one longitudinal edge frees perform very

poorly. To improve the performance of these elements, lips are provided which act as

stiffeners. Therefore, these elements behave as stiffened elements.

For long columns, the critical loading the ultimate load. That is, columns do not process

any post buckling strength. However, plates with edges supported or stiffened parallel to

the direction of compression; possess additional strength beyond 6cr which is known as

the post-buckling strength.

17

1Z{i Xi/t)2

Boo- edition Type of Stress

Value of k for ION Plote

Cornprsscr 40

Compression 6.97 xed

Compression 3.425

Compress,cn 1 .277

s.s. SS

Cornpessc 5. 42

5.35

S.S.

77 - tc—j Bending

Table:- 3.1, Values of 'k'

IS 801:1975 lays down the design specifications based on the working stress method.SP6

(part 5): 1980[27] provides a commentary on the provisions of IS 801, the design tables

and curves and design.

3.4.2. Effective Design Widths of Stiffened Elements

Load Determination (For rectangular/square hollow sections):

w 487 If, —~-----, b=w,

i.e. the flanges of rectangular/square hollow sections are fully effective,

18

w 487 If, —>-

\1?,

b_ 671 133

t V J 1 (w/t). J

Deflection Determination (For rectangular/square hollow sections):

w 630 If, —s—, b = w,

i.e. the flanges of rectangular/square hollow sections are fully effective,

w 630 If, t > ,

b_ 5u~ r 17'

t L1 (w/t)VJ

3.4.3 Tension Member

Tension members are linear members in which axial forces act causing elongation

(stretch). Such members can sustain loads up to ultimate load, at which stage they may

fail by rupture at a critical section. However, if the gross area of the member yields over a

major portion of its length before the rupture load is reached, the member may become

nonfunctional due to the excessive elongation.

3.4.3.1 Design criteria for Tension Member (IS: 800-1984)

Axial Stresses:

The permissible stress in axial tension, o, in N/mm2 on the net effective area

of the sections shall not exceed.

aSt =0.6xfy

Where, fy = minimum yield stress of steel (N/mm2)

3.4.3.2. Design Steps for Tension Member (IS: 800 – 1984)

➢ The net area required (A1et) to carry the design load P is obtained by the equation,

19

Anet = P/Oat

➢ The net area calculated thus, is increased suitably (25 % - 40 %) to compute the

gross sectional area. From SP: 6 suitable section is provided whose cross-sectional

area is greater than computed gross sectional area.

➢ The number of bolts required to make the connection is calculated. These are

arranged in a suitable patterns and the net area of the section provided is

calculated. This should be more than the net area calculated.

➢ The slenderness ratio of the member is checked as per Table-3.1 of IS:800 (1984).

3.4.4 Compression Member

Columns and struts are termed long or short depending on their proneness to

buckling. If the strut is short, the applied forces will cause a compressive strain, which

results in the shortening of the strut in the direction of the applied forces. Under

incremental loading, this shortening continues until the column squashes. However, if the

strut is long, similar axial shortening is observed only at the initial stages of incremental

loading. Thereafter, as the applied forces are increased in magnitude, the strut becomes

unstable and develops a deformation in a direction normal to the loading axis.

Buckling behavior is thus characterized by deformations develops in a direction (or plane)

normal to that of the loading that produces it. Buckling occurs mainly in members

subjected to compressive forces. If the member has high flexural stiffness, its buckling

resistance is high. Also when the member length is increased, the buckling resistance is

decreased. Thus the buckling resistance is high when the member is stocky and is low

when the members are slender.

3.4.4.1 Effective Length of Compression Member

Effective length is the distance between the points of inflection in the buckled

mode. The effective column length can be defined as the length of an equivalent pin-

ended column having the same load carrying capacity as the member under consideration.

The smaller the effective length of a particular column, the less possibility of lateral

. buckling, and the greater its load carrying capacity.

20

Boundary C: onclitiOns Schematic Effective At onfe end At the other end representation Length Tris1aiioii .Riiwtation Translation Rotation

Restrained Restrained Free Free --...._.-.._._......- ....--........ . -....-.".."-.. - ....... - ..... - 20L

Free Restrained Free pm

Restrained -.-..-.-........

Free. -

Restrained ..... .......

Free - ----

1 .0L ......................

Restrained Restrained Fi'e Restrained j

1.2L

Restrained I Restrained I Restrained I Free I

Restrained Rest rained Restrained Restrained - 0.65 L

lable:- 3.2, Fttective length of prismatic compression member

Note: L is the unsupported length of the compression member.

3.4.4.2 Design criteria for Compression Members (IS: 800-1984)

Evaluation of design compressive strength (Cl-5. 1)

> The direct stress in compression on the gross sectional area of axially loaded

compression members shall not exceed (0.6 x fy) nor the permissible stress o,

calculated using the following formula,

fcbxfy Ubc = 0.66 1/

[(fcb)n ()fl] TI

fy

Where, ac = permissible stress in axial compression, in N/m 2 m ,

fy = yield stress in steel, in N/mm2 ,

fcc elastic critical stress, in N/mm2,

E = elastic critical stress in compression, = (n2 x E) / X2 ,

2 (= KL/r) = slenderness ratio of the member, ration of the effective length

to appropriate radius of gyration, and

n = a factor assumed as 1.4

21

3.4.4.3 Design steps for Axially Loaded Compression Member (IS: 800-1984)

➢ Average allowable compressive stress in the section is assumed. It should not be

more than the upper limit for the column formula.

➢ The cross sectional area required to carry the load at the assumed allowable stress

is computed.

Arequired = 0

Allowable Compressive stress

Where,

A = Tentative cross sectional area required, in mm2.

P = Load on column, in Newton

➢ Section that provides the estimated required area is selected. The section is so

chosen that the minimum radius of gyration of the section selected.

➢ The effective length of the column is calculated on the basis of end conditions and

the slenderness ratio is computed (X = 1/r), which should be less than the

permissible slenderness ratio (Table 3.1 of code).

> For this estimated value of slenderness ratio, the maximum allowable compressive

stress, 6ac is calculated from the Table 5.1 of the code.

> The load carrying capacity of the member is computed by multiplying the

maximum compressive stress thus obtained with the cross sectional area provided.

This value of the load carrying capacity of the member should be more than the

load to be supported by it.

3.5. Relative merits of tubular sections

1) Tube as Compression Members

> It is common knowledge with structural designers that allowable stresses in

compression members (Axially Loaded) are dependent on slenderness ratio, i.e.

the ratio of effective length and least radius of gyration. The effective length

depends on the end fixity and restraint. It is more often than not that the effective

length of members in a tubular welded construction will be as effective as in any

other form of construction. It is because the complete cross section is likely to be

connected to the restraining member, provided, of course, the end preparation is

adequate and accurate, offering complete bearing contact. As far as radius of

22

gyration is concerned, the larger its value, the stronger the structure. Therefore, in

all strut design it is essential to choose sections with the largest radius of gyration

for any given weight per meter.

➢ Conventional sections, such as beams, channels, angles have varying values of

radius of gyration about different axes and to reduce the slenderness ratio about

weaker axes to an economical figure, it is often necessary to introduce additional

members to act as bracing, in order to reduce the effective length. Such members

can be omitted, or reduced in number, since tubes have same radius of gyration

about all axes. For any given weight/meter, radius of gyration in a tube has the

largest possible value, and therefore, for a strut, no other sections could be thought

of as more efficient.

2) Tubes as Tension Members

➢ Load in a tension member is absorbed by the net cross sectional area deducting the

area for bolt holes in case of bolted connection. In welded connection, gross area

of the tube is effective, while in single angles, only a portion of the unconnected

leg may be considered effective, as the vertical or horizontal C.G. lines do not

divide the cross sections symmetrically. Thus for any given load, the sectional

area required in a tube will be less than in a single angle, which is generally the

alternative section.

3) Torsional Quality of Tubes

➢ Tubes, being enclosed sections and symmetrical about all axes, are ideal for taking

care of torsion. Torsional stresses get distributed equally over the whole section.

However, in case of an open section, unsymmetrical in nature, such quality is not

obtained.

4) Advantages in Terms of Thickness of Material

➢ Tubular sections are less likely to be affected by weather hazards provided they

are galvanized or are given adequate coats of requisite paints, depending on the

environmental conditions, and properly sealed at ends to prevent corrosion. That

is why, in case of tubes exposed to weather, the minimum thickness can be as

small as 8 gauge and when not exposed to weather, it may be even less i.e. 10

23

gauge. So, obviously, in case of angles and plates, even if the design requirement

does not demand a thickness as high as 8 mm thick, we may have to provide it.

This, in all likelihood, facilitating saving in material.

5) Aesthetic Appeal

➢ When the requirement of aesthetic appeal of a structure, tubes offer a more

pleasing appearance than the irregular shapes of other sections. In any case, when

aesthetics is a primary consideration, it will be ideal for an engineer to decide

upon the shape and proportion of the structure, in consultation with an architect. It

must be borne in mind that tubes may enable one to avoid a large cluster of

complex bracing, leading a rather ugly appearance to a structure. Lesser the

members, the simpler and more attractive will appear the structure.

24

3.6. Deflection criteria

The deflection under serviceability loads of a building or a building component

should not impair the strength of the structure or components or cause damage to

finishing's. Deflections are to be checked for the most adverse but realistic

combination of service loads and their arrangement, by elastic analysis, using a load

factor of 1.0. Table 3.3 gives recommended limits of deflections for certain structural

members and systems. Circumstances may arise where greater or lesser values would

be more appropriate depending upon the nature of material in element to be supported

(vulnerable to cracking or not) and intended use of the structure, as required by client.

Typc of Difltlioi 0*4 Lead Member Suppoi1b g hlulmum lluildinp~ DerA i"

(t) (2a (3) (4) (S) ()

Lis, fond/ Wind Io d Purls snd C rls Fa'tic cladding $pan~1 G SpnnftAO BriittcsJadding

f Ela~t{e cladding. Span/240 Li rc Id 5innatc +pun

Briele cladding Sponl3t)0

Elastic cladding Span/120 Live load Cdntilcvci spin

HritdeCladding Spbnl150

moiled Metal Shecong SpanI110 V Livcloadf W and laab fixttct avppotting

Piaslerad Sheering Span/240

Crane load (Manual rrtntry Cront SlrunJ5(Ji) upetatlon )

C tdnc fud (Llulric operattivn up tO 50 t1 {;entry Crone Span;150

Crane load (Electric :rer:,t»~it~,veT i1,) Cinntry crane SpawI000

C.•aasticcludding 13eighafl50 :~c,cranwr; Column

)vlastlnry/Efiu)e eladdir►g 1

Heig)I11240

Crmne (u solutc) Spanl4ttO

Crane + wind Gantry (littral) t Relative dip iacerncnt i between all sapponing 10 mm 9 crane

Gantry (Elastic cladding; Metgt~

Crane+wind Coluinnffrontc 'pendent .operated)

Gantry (Brittle cladding, cab MelghtfddlQ nperated)

EIrin rns not 3uacepiibIc to Spa .1m

tho load floor and Roof dt`'uking Elemns suscepfble to 5paN36O cryckin{

C 1 lcmentz not sauepti6k to S nri50 decking ' iVt lwtl Carib/ *w

1 Elcnlc ltla Susccpiibic to Spanilsa clwking

Wind 13uiicling Etuu cladding ic HeightI3U0

i Brittleclattlding Me1ght/500

Wind InicrscrucyUrifi ^- Swrcyicilshtl30O

Table:- 3.3, Deflection Limits

25

CHAPTER- 4 PROBLEM DEFINITION

4.1 Common Data of the framed Truss:

An internal gable framed truss with hinge support of an Industrial building of two

different spans viz., 30m & 40m is considered for the present study. For the purpose of

study the loading on the frame is taken as IOkN/m along the top chord and also the

column geometry & member cross section is kept fix for given span and eave height is

kept at 6m in all the cases.

4.2 Materials used and their properties:

a) High Strength Steel, with yield strength to be fy =31 OMPa

b) Unit mass of steel, p = 7850 kg/m3

c) Modulus of elasticity, E = 2.0 x 105 N/mm2(MPa)

d) Poisson ratio, µ = 0.3

4.3 Detailed explanation of the problem considered:

If economy and deflection are disregarded trusses may be theoretically built to

almost any proportion. An understanding of the interrelated factors that contributes to

performance and economy will aid the designer in selecting the best system.

The aim of the present study is to obtain variation in deflection and weight with

various geometrical parameter of roof truss of framed truss.

26

Roof angle:

Roof angles considered for study are 5°, 6° and 7°. Since these angles give more

suction over a large span, the connectivity of the roof sheeting with purlins may become a

problem. But this problem can be overcome in Pre-engineered buildings because of using

closely spaced self tapping screws throughout the length of the purlin. This range of roof

angle is taken under the consideration of draining the storm water. If the roof angle

considered is beyond 7°, for larger spans the height above the eave level to ridge level

will be high, which is undesirable. So in the present study, roof angle varies from 5° to 7°.

Depth of the truss at Eave and Ridge:

There is no standard method or guidelines available for deciding the depth of

rafter of framed truss at ridge and eva level. It has been observed that with increase in

depth there will be better deflection control but truss height and weight also increase.

Based on the number of trails suitable ranges for eave and ridge depth is decided for the

study purpose.

Number of panel:

The number of panel usually should be determined by reasonable to chord sizes,

rather than by any fix formula. Desirable panel length will usually be in the range of 1.5m

to 2.8m.

Span = 30 m Span = 40m

Truss Geometric Parameters Truss Geometric Parameters

12 to 20 1300 to 1500 600 to 1000 20 to 28 1500 to 1700 600 to 1000

Table:4.1 Varing range of various parameters for the study porpose

P

Member cross section:

High strength steel hollow square sections available in market which conforms to

IS 4923 are used for the present study:

SHS (BxB)mm

Thick ness mm

Sec Area

(A) cm2

Unit W

kg/m

Mome. of Iner. Radi. of Gyr. Elastic Modu. Torsional Const. B

lxx cma

lyy cm4 rxx cm ryy

cm Zxx cm3

Zyy a cm3 cm 3 cm

2 1.74 1.36 1.48 1.48 0.92 0.92 1.19 1.19 2.29 1.68 25x25 2.6 2.16 1.69 1.72 1.72 0.89 0.89 1.38 1.38 2.68 1.92

3.2 2.53 1.98 1.89 1.89 0.86 0.86 1.51 1.51 2.96 2.07 2 2.3 1.8 3.36 3.36 1.21 1.21 2.1 2.1 5.3 3.05

32x32 2.6 2.88 2.26 4.02 4.02 1.81 1.81 2.51 2.51 6.45 3.63 3.2 3.42 2.69 4.54 4.54 1.15 1.15 2.84 2.84 7.41 4.07 2.6 3.51 2.75 7.14 7.14 1.43 1.43 3.76 3.76 11.51 5.49

38x38 3.2 4.19 3.29 8.18 8.18 1.4 1.4 4.3 4.3 13.45 6.28 4 5.03 3.95 9.26 9.26 1.36 1.36 4.87 4.87 15.67 7.12

2.6 3.72 2.92 8.45 8.45 1.51 1.51 4.22 4.22 13.63 6.2 40x40 3.2 4.45 3.49 9.72 9.72 1.48 1.48 4.86 4.86 16 7.12

4 5.35 4.2 11.07 11.07 1.44 1.44 5.54 5.54 18.75 8.12 2.6 4.76 3.74 17.47 17.47 1.92 1.92 6.99 6.99 28.53 10.37 2.9 5.25 4.12 18.99 18.99 1.9 1.9 7.6 7.6 31.15 11.23

50x50 3.6 6.35 4.98 22,15 22.15 1.87 1.87 8.86 8.86 36.58 12.98 4.5 7.67 6.02 25.5 25.5 1.82 1.82 10.2 10.2 41.99 14.68 2.6 5.8 4.55 31.33 31.33 2.33 2.33 10.44 10.44 50.08 15.52 3.2 7.01 5.5 36.94 36.94 2.3 2.3 12.31 12.31 60.02 18.31

60x60 4 8.55 6.71 43.22 43.22 2.26 2.26 14.52 14.52 72.41 21.62 4.8 10.1 7.85 49.22 49.22 2.22 2.22 16.41 16.41 83.86 24,51 3.2 8.54 6.71 66.32 66.32 2.79 2.79 18.42 18.42 106.81 27.47

72x72 4 10.47 8.22 79.03 79.03 2.75 2.75 21.95 21.95 129.85 32.78 4.8 12.31 9.66 90.31 90.31 2.71 2.71 25.09 25.09 151.55 37.55 3.2 9.57 7.51 92,71 92.71 3.11 3.11 23.18 23.18 148.55 34.6

80x80 4 11.75 9.22 111 111 3,07 3.07 27.76 27.76 181.22 41.49 4.8 13.85 10.9 1127.6 127.6 3.04 3.04 31.89 31.89 212.26 47.77 3.6 12.32 9.67 156.5 156.5 3.56 3.56 34.21 34.21 251.17 51.14

91.5x91.5 4.5 15.14 11.9 187.6 187.6 3.52 3.52 41 41 306.78 61.4 5.4 17.85 14 215.7 215.7 3.48 3.48 47.14 47.14 359.76 70.77 4 14.95 11.7 226.4 226.4 3.89 3.89 45.27 45.27 364.75 67.5

10Ox100 5 18.36 14.4 271.1 271.1 3.84 3.84 54.22 54.22 441.84 80.54 6 21.63 17 311.5 311.5 3.79 3.79 62.29 62.29 511.8 92.06

4.8 20.28 15.9 393.3 343.3 4.4 4.4 69.3 69.3 637.45 103.89 113.5x113,5

5.4 22.6 17.7 432.6 432.6 4.38 4.38 76.23 76.23 708.69 114.41 4.8 23.83 18.7 634.4 634.4 5.16 5.16 96.12 96.12 1018.3 144.11

132x132 5.4 26.6 20.9 700.1 700.1 5.13 5.13 106.1 106.1 1134.3 159.18 4 22.95 18 807.8 807.8 5.93 5.93 107.7 107.7 127346 161.38 5 28.36 22.3 982.1 9&2.1 5.89 5.89 131 131 1569.1 196.38

150x 150 6 33.63 26.4 1146 1146 5.84 5.84 152.8 152.8 1856.2 229.44 8 43.79 34.4 1443 1443 5.74 5.74 192.4 192.4 2405.8 290.12 4 27.75 21.8 1422 1422 7.16 7.16 158 158 2224.3 236.76

5 34.36 27 1737 1737 7.11 7.11 193 193 2747.9 289.4 180x180 6 40.83 32.1 2037 2037 7.06 7.06 226.3 226.3 3259.2 339.65

8 53.39 41.9 2591 2591 6.97 6.97 287.9 287.9 4246.2 433.32 6 50.43 39.6 3813 3813 8.7 8.7 346.7 346.7 6034.5 520.18 8 66.19 52 4895 4895 8.6 8.6 445 445 7897.5 668.99

220x220 10 81.43 63.9 5887 5887 8.5 8.5 535.2 535.2 9549.2 796.48 12 96.14 75.5 6793 6793 8.41 8.41 617.6 617.6 11117 915.37

Table:- 4.2, Properties of Square Hollow sections

W

4.4 Analysis:

The models of all the cases have been analyzed and designed using STAAD Pro-

2007 software. The deflection at the ridge, stress ratio, and weight of the frame for each

analysis has been taken. The sequence of the study is given in the next page.

29

'-I -

C - V44

0

4701 0 0

iLl iLl

5 U S '-I

LI

V.- - 0 CD

0 0

iLl pl

c;L4

0, I-

Q

C

I 0

CHAPTER 5 RESULTS

The results obtained from the analysis of different models using the STAAD Pro-

2007 software is noted down systematically. The same results have been presented in a

lucid manner in a combination of graphical and tabular form here in this chapter.

The order of the results presented in this chapter is given below:

5.1 Result for 30m span

5.1 .1 Effect of increasing Eva & Ridge depth

5.1.2 Effect of Roof angle

5.1.3 Effect of number of panels

5.2 Result for 40m span

5.2.1 Effect of increasing Eva & Ridge depth

5.2.2 Effect of Roof angle

5.2.3 Effect of number of panels

In the above sections, effect of Truss geometry (i.e. Eave depth, Ridge depth,

Roof angle), effect of Truss web pattern (i.e. Warren, Pratt and Howe) and number of

Truss Panels, on control of deflection, weight of truss and finally the percent capacity

utilization of various members has been presented in the form of graphs and figures.

5.3 Design of typical Framed Truss

5.3.1 Design of typical framed truss for 30m span

5.3.2 Design of typical framed truss for 40m span

In this section, design of an intermediate framed truss for an industrial roof

system with tubular sections, Pratt web pattern, and possible governing loadings has been

carried out for span of 30m and 40m. All design parameters and design results, i.e. truss

deflection, weight and finally the percent capacity utilization of various members has

been presented in the form of graphs and figures.

31

10 JN/m

Fig:- 51,1, Various terminology used for Framed-truss

Om Load t

Variable parameters for the study

Roof Angle Eva Depth (ED) Ridge Depth (RD)

(mm) (mm)

600

1° 1300 700

8° 1400 800

9° 1500 900

1000

Fixed Parameters for the Study purpose

Truss Geometrical Parameters:

Clear Span: 30m Column Clear height :6m

Structural System: Framed Truss Web Pattern: Pratt

Number of panels :18

Member Cross-sectional parameters:

Truss Members Column Members

Parameter SHS Cross-section

( )


(mm2)

Top Chord (Rafter) 132x132x4,8 (R3) Chord Members 150x150x5 (R4)

Bottom Chord 132x132x4,8 (R3)

Vertical web members, 60x6Ox2.6 (R1) Web Members 91.5x91.5x3,6 (R5)

Inclined web members. 1002100x4 (R2)

5.1.1 Effect of truss depth at Eave and Ridge (Span=30m):

Objective: To study effect of increasing truss depth at Eave and Ridge on the weight and deflection of Framed-Truss, at various-

-roof angles, with all other parameters kept constant,

Fig:- 5.1.2, Member cross-section reference

Span: 30 m Roof angle: 5°

1.24 2830

w....__._ ... ............. 2810 X D a

0 1.12

1.06 -- 2770

1 wr - 2750 0 y,, C1

Y t

0.94 --- 2730 ~+

3 D3 0.88 - ...._- ...__.. ....._...._._ .................... 2710

0.82 D 2690

0.76 (._..__..._...__.__._ __ ..__...._ ._... —._.. - ._............ — — - _.........._.. _ -- 2670

600 650 700 750 800 850 900 950 1000

Truss depth at ridge (mm)

Fig: - 5.1.3, Variation between i) Truss depth at ridge Vs Deflection Ratio and

ii) Truss depth at ridge Vs Weight of the frame

Notation Description

Deflection &

D 1 & W 1 Weight for Truss with Eave depth 1300 mm

Deflection &

D2 & W2 Weight for Truss with Eave depth 1400 mm

Deflection &


Comments:-

a) As the Eave depth increases from

1300mm to 1400mm and from 1400mm

to 1500mm the percentage reduction in

maximum deflection is ii and 10.

b) As the Eave depth increases from


to 1500mm the percentage increase in

weight of the Truss frame is 0.162 and

0.164.

c) Frame become safe as per deflection, for

all Eave height from web depth at ridge = 950 mm.

d) As Eave depth of the truss increases the overall height of the truss also

increase.

33

an

2800 m

2780

2760 0 r

2740

3 2720

2700

1.06 0 M cc 1 C 0

0.94

0.88

650 700 750 800 850

Truss Depth at Ridge (mm)

0.7

600 900 950

2680

1000

1.18

1.12

2840

2820

0.82

0.76


Fig: - 5.1.4, Variation between i) Truss depth at ridge Vs Deflection Ratio and



Deflection &

D1 &W1 Weight for Truss with Eave depth 1300 mm

Deflection &


Deflection &


Comments:-

a) As the Eave depth increases from 1300mm to

1400mm and from 1400mm to 1500mm the

percentage reduction in maximum deflection is

10.5 and 10.

b) As the Eave depth increases from 1500mm to


percentage increase in weight of the Truss

frame is 0.165 and 0.164.

c) Frame become safe as per deflection, for all

Eave height from web depth at ridge = 900mm.

d) As Eave depth of the truss increases the overall height of the truss also

increase.

34


1.18 2840

1.12 2820 V v

1.06 _ 0 2800 E

Y

1 LL

2780 N i L

0 94 ........ 2760 0

ao 0 .88 ........ .........._. .._....._.- – — 2740 a

0.82 -._.. _ .. — — 2720

0.76 _ — 2700

0.7 — ...__._.__..__ - - - 2680

600 650 700 750 800 850 900 950 1000

Truss Depth at Ridge (mm)

Fig: - 5.1.5, Variation between i) Web depth at ridge Vs Deflection Ratio and

ii) Web depth at ridge Vs Weight of the frame

Comments:-



percentage reduction in maximum deflection

is 10 and 11.

b) As the Eave depth increases from 1300mm to




c) Frame become safe as per deflection, for all

Eva height from web depth at ridge = 800mm.

d) As Eave depth of the truss increases the

overall height of the truss also increase.


Deflection & Weight for Truss Dl &W1 with Eave depth 1300 mm

Deflection & D2 &W2 Weight for Truss

with Eave depth 1400 mm

Deflection & Weight for Truss D3&W3 with Eave depth 1500 mm

35

5.1.2. Effect of roof angle (span: 30m):

Span: 30m Depth at Eave: 1400mm

Fig: - 5.1.6, Depth at ridge Vs Deflection Ratio for various roof angles [web depth at eave =1400mm]

Comments:-

a) Percentage reduction in deflection with

increase in roof slope from 5° to 6° and 6°

to 7° is in range of4 to 7.

b) As the depth at ridge increase from

600mm to 700mm the deflection control is

better and after that the deflection control

with increasing the truss depth at ridge,

reduces gradually.

c) The Truss becomes safe in deflection for

Notati Description on

Deflection of D1 Truss with Roof 5°



each roof angle at ridge depth 800mm and above.

d) At Roof angle 7° the truss becomes safe in deflection at all ridge depth considered.

36

Warren Web Pattern

Howe Web Pattern

5.1.3 Effect of Number of Panels (Span=30m):

Objective: To study effect of increasing number of panels on the deflection of Framed-Truss for Pratt;

Howe and Warren web patterns, with all other parameters kept constant, 10 KNIm

Pratt Web Pattern

Fig: 5,1.7, Framed-truss with various Web Patterns

Pratt web pattern : 6°

Range of panel number for the study: 12, 14, 16, 18, and 20

Member Cross-sections used



(mm)


(mm )

Top Chord (Rafter) 132x132x4.8 Chord Members 150x150x6

Bottom Chord 132x132x4.8

Vertical web members. 60x60x2,6 Web Members 100x100x4

Inclined web members. 1133x113,5n45

Warren web pattern : 6°)

Range of panel number for the study:

6, 7, 8, 9, and 10

Member Cross-sections used

Truss Members Column Members Parameter SHS Cross-section

(mm)


(mm')

Top Chord (Rafter) 150x150x6 Chord Members 150x150x6

Bottom Chord 150x150x6

Inclined web members. 132x132x4,8 Web Members 100x100x4

Howe web pattern : 6°)

Range of panel number for the study:

12, 14, 16, 18, and 20

Member Cross-section used:

Truss Members Column Members Parameter SHS Cross-section ( z Parameter SHS Cross-section

(mmr)

Top Chord (Rafter) 150x150x6 Chord Members 1502150x6


Vertical web members. 72x12x3.2 Web Members 100x100x4

Inclined web members. 1135x1135x4.8

Web pattern: Pratt Roof angle: 6° Span: 30m

Depth at Eave: 1400mm Depth at Ridge: 700mm

116.8

116

E 115.2

112.8

112

10 12 14 16 18 20 22

Number of Pannels

Fig:-5.1.8, Number of Panels Vs Deflection [truss depth at eave =1400mm]

Comments:-

a) As the number of panel increase deflection control is better to certain number

of panels there after increase in number of panels doesn't have significant

control over deflection.

b) For number of panel 18 the truss will have batter control on deflection.

c) With increase in number of panels, number of connection also increases.

38

Web Pattern: Warren Roof angle: 6° Span: 30m

Depth at.Eva:.1400mm Depth at Ridge: 700mm

105.5 --- __.....__.._..._ .__-

.. 104. D1

E E

101 0

99.5 w

D2D 1

98

D1 96.5 ~ ..._ ._. _

D

95

93.5 -_ ... .~.

5 6 7 8 9 10 11 12

Number of Pannels

Fig:-5.1.9, Number of Panels Vs Deflection [truss depth at eave =1400mm

Comments:-

a) As the number of panel increase deflection

control is better to certain number. of panels

there after increase in number of panels doesn't

have significant control over deflection.


D1 With even number panels

D2 With odd number panels

b) For Warren truss two pattern of variation in

deflection (i.e. D1 & D2) with number of panels is observed. This is due to

change in the arrangement of web member of the panels connected with

column (as shown in Figures below).

Roof Truss

eb member Web member

-. Column Truss -a- oiumnTruss

For odd number of panels For even number of panels

39

c) For number of panels 11 the truss will have batter control on deflection, but

for economy we have to check for number of panels 10 also.

d) With increase in number of panels, number of connection also increases.

Web Pattern: Howe

Depth at Eva: 1400mm

i 112

110.5

E 109 E

C 107.5

u 106

104.5

103

101.5

Roof angle: 6° Span: 30m

Depth at Ridge: 700mm

100 I-. __.._. __.4 ..._.__.._... _........... 10

12 14 16 18 20 22

Number of Pannels


Comments:-

a) As the number of panel increase deflection control is better up to certain

number of panels there after increase in number of panels doesn't have

significant control over deflection.

b) For number of panels 20 the truss will have batter control on deflection, but



40

10 KNIm

w wu wu

Fig: .5.2.1 Various terminology used for framed-truss

Variable parameters for the study

Roof Angle Eva Depth (ED) Ridge Depth (RD)

(mm) mm)

600

1° 1500 700

8° 1600 800

9

0

1700 900

1000

Fixed Parameters for the Study purpose

Truss Geometrical Parameters: -

Clear Span : 40m Column Clear height : 6m

Structural System: Framed Truss Web Pattern: Pratt

Number of panels :24

Member Cross-sectional parameters:



(am)


(ce)

Top Chord (Rafter) 150x150x8 (R3) Chord Members 150z150z8 (RI)

Bottom Chord 150z150z8 (R3)

Vertical web members. 72z12z3,2 (R6) Web Members 113.5x113.5x4.8 (R4)

Inclined web members. 100x100x5 (R5)

5,2.1 Effect of truss depth at Eave and Ridge (Span=40m)

Objective: To study effect of increasing depth at Eave and Ridge on the weight and deflection of Framed-Truss, at various-

-roof angles, with all other parameters kept constant,

Fig: -5.2.2 member cross-section reference


1.18 -- - - — 5640

1.12 vvs

1.06 -- -- v 5570 W3" E

1 ~.~ _ 5535 W DL """ VVL

wiswniw*i~ O CA

0.94 5500

0.88 = 3 5465

0.82 _._._.... __..___.__. —__ _ 5430

0.76 .......... ......_ ..__........ - .. - 5395

0.7 h---- -___ 5360

600 650 700 750 800 850 900 950 1000

Depth of Truss at Ridge (mm)

Fig:-5.2.3, Variation between i) Truss depth at ridge Vs Deflection Ratio and


Comments:-

a) As the Eave depth increases from 1500mm

to 1600mm and from 1600mm to 1700mm

the percentage reduction in maximum

deflection is 9.5 and 8.5.

b) As the Eave depth increases from 1500mm

to 1600mm and from 1600mm to 1700mm

the percentage increase in weight of the

Truss frame is 0.165 and 0.164.

c) Frame become safe as per deflection, from

web depth and ridge = 900mm.




Deflection &

Dl &W1 Weight for Truss with Eave depth 1500mm

Deflection & Weight for Truss D2 & W2 with Eave depth 1600mm

Deflection & Weight for Truss D3 & W3 with Ea depth 1700 mm

42


1.18 — — — — --.__.._

-------- —._.._._.— -_---- ..___._........-_ .. 5650

1.12 5600

1.06 o

.... _... ~...._.-~. _. ~

3 I 5550

C

0.94

vA

5500

0.88 5450

0,82 —__.-..__.

0.76 ------_ 3 5400

0.7 5350

600 650 700 750 800 850 900 950 1000



ii) Truss depth and ridge Vs Weight of the frame

Comments:-

a) As the Eave depth increases from


to 1500mm the percentage reduction in

maximum deflection is 9.3 and 8.2.

b) As the Eave depth increases from


to 1700mm the percentage increase in

weight of the Truss frame is 0.165 and

0.164.

c) Frame become safe as per deflection,

from web depth at ridge = 700mm.




Deflection & Weight for Truss D 1 & W 1 with Eave depth 1500 mm

Deflection & Weight for Truss D2 & W2 with Eave depth 1600 mm

Deflection &


43

Span: 40 m Roof angle: 70

1.12 _..._.__._..._..._........-,._.. _.,,._._.....__..... _-_...._ _m ...__._ _._.... _._.._._....._.._ 5700

1.06 --4

5650 Y

0 1 ........ ... ..W3-- 5600 W3 LL

3

0 0.94 5550 2 o

0.88 5500

uLz

0.82 -- -- 5450

0.76 3 b3 5400

0.7 .. ..__.... .......... ........_ _ . ....... ......_ . .... _. _. _ ................... 535

600 650 700 750 800 850 900 950 1000




Comments:-



percentage reduction in maximum deflection

is 9 and 8.

b) As the Eva depth increases from 1500mm to




c) Frame become safe as per deflection, from

web depth and ridge = 600mm.


Deflection & Weight for Truss

D1 & W1 with Eave depth 1500 mm

Deflection & Weight for Truss

D2 & W2 with Eave depth 1600 mm

Deflection &


d) As Eave depth of the truss increases the overall height of the truss also increase.

44

5.2.2 Effect of roof angles (Span: 40m)

Span: 40m Depth at Eave: 1500mm

600 650 700 750 800 850 900 950 1000

Depth at Ridge (mm)

Fig:-5.2.6, Depth at ridge Vs Deflection Ratio for various roof angles [Truss depth at eave =1500mm]


Deflection of Dl Truss with Roof

5°

Deflection of D2 Truss with Roof

6°

Deflection of D3 Truss with Roof

7°

Comments:-

a) Percentage reduction in deflection with

increase in roof slope from 5° to 6° and 6° to

7° is in range of 7 to 9.

b) As the depth at ridge increase the deflection

control is better to certain web depth and after

that increasing the web depth doesn't have

significant control in deflection.

Th T b -r • dfl -r h c) e russ ecomes sa e in e ection or eac

roof angle at ridge depth 900mm and above.

d) At Roof angle 7° the truss becomes safe in deflection at all ridge depth considered.

45

Pratt web pattern : 6°) ge of panel number for the study:

20, 22, 24, and 26 nber Cross-sections used :


(mm) Parameter SHS Cross-section

(MM2)

)p Chord (Rafter) 150x150x8 Chord Members 15Ox15Ox8


:ical web members. 80x80x3.2 Web Members 113.5x113.5x5.4

ned web members. 100x100x5

Warren web pattern (RA : 60 ige of panel number for the study:

11, 12, 13, and 15 tuber Cross-sections used:

Truss Members Column Members Parameter SITS Cross-section

( 2) Parameter SHS Cross-section

(mm

~p Chord (Rafter) 150x15Ox8 Chord Members 150x15Ox8

Bottom Chord 150x15Ox8

fined web members. 100x100x5 Web Members 113.5x113.5x5.4

Howe web pattern : 6°) ►ge of panel number for the study:

22, 24, 26, and 28 nber Cross-sections used:


(mm)

Parameter SHS Cross-section (mm

)p Chord (Rafter) 15Ox15Ox8 Chord Members 150x15Ox8


:ical web members. 80x8Ox3.2 Web Members 113.5x113.5x5.4

ned web members. 100x100x5

5.2.3 Effect of Number of Panels (Span=40m):

Objective: To study effect of increasing number of panels on the deflection of Framed-Truss for Pratt,

- Howe and Warren web patterns, with all other parameters kept constant. 10 KN/m

Pratt Web Pattern

Truss Pannel

Warren Web Pattern

} Howe Web Pattern

Fig: 5.2.7, Framed-truss with various Web Patterns

Web pattern: Pratt Roof angle: 6° Span: 40m

Eave depth: 1600mm Ridge depth: 800mm

16 18 20 22 24 26 28

Number of Pannels

Fig:-5.2.8, Number of Panels Vs Deflection [truss depth at cave =1600mm]

Comments:-

a) As the number of panel increase deflection control is better to certain



b) For number of panel 24 the truss will have batter control on deflection.


47

Web Pattern: Warren Roof angle: 6° Span: 40m

Depth at Eave: 1600mm Depth at Ridge: 800mm

---

D1

150 ~

149 .. ......... .... ......._..._ . .. ............_... ............._ _. ........ ............

E E

0 147

146. .... .

145 ~--

144 —..__ ._ __.._..._._...._.._ .__.._...... _.. _ ._ D2

143 --

10 11 12 13 14 15 16

Number of Pannels

Fig:-5.2.9, Number of Panels Vs Deflection [truss depth at eave =1600mm


With Even Number Dl of panels

With Odd Number D2 of panels

Comments:-

a) As the number of panel increase deflection

control is better to certain number of panels

there after increase in number of panels doesn't

have significant control over deflection.

e) For Warren truss two pattern of variation in

deflection (i.e. Dl & D2) with number of panels is observed. This is due to

change in the arrangement of web member of the panels connected with

column (as shown in Figures below).

Roof Truss Roof Truss

Web member Web member

a-. Column Truss 4* Colurnn Truss

For odd number of panels For even number of panels




Web Pattern: Howe Roof angle: 6° Span: 40m

Depth at Eave: 1600mm ..................................................................................................... .

Depth at Ridge: 800mm

159.3

158.7 .._

----

_. .

-

E

^ 158.1 ..._- ... ....... .. ...... ._..._.._ ......_ -

E 157.5 __._. _ ___

156.9 ......._. _...._ ..............._....., .,_.... ........ _... ....... ...___ __ _...._.. _.___... _._..__...._.,__.._...___..

O 156.3

155.7 -..__._.........,

1545

18 20 22 24 26 28 30

Number of Pannels


Comments:-

a) As the number of panel increase deflection control is better up to certain






49

5.3 Design of -typical framed truss:

In this section design of typical intermediate framed truss with tubular

sections, and Pratt web pattern is carried out for clear span of 30m and 40m. The

design has been carried out with the help of STAAD Pro-2007, as per IS: 800-1984.

Since uniformly distributed load is taken on the top chord of the truss, it is designed

assuming that it is simply supported but continuous member. The effective length

factor (K) for compression member in a truss can always be conservatively taken as

equal to 1. However, due to considerable end restrains present in truss the effective

length factor (K) is generally less than 1. The maximum slenderness ratio of

compression Members has been restricted to be less than 180 and tension members to

be less than 250.

Common Data:

➢ High-Reflecting Profiled Galvalume sheet as roofing materials.

➢ Square tubular section used for purlins.

➢ Column clear height is equal to 6m.

➢ The framed truss is supported with pinned support at both ends.

➢ Brick wall as side cladding.

➢ The trusses are spaced at 6 m apart.

➢ Purlins spacing is limited to 0.77 m.

Loading

1) Dead load

Self-weight of the Framed-Truss is considered directly through the self-weight command of STAAD-pro 2007.

Dead load of roof sheeting:

The weight of 24 gauge (0.63mm thick) Galalume sheet as 4.8 kg/m2. To include the

additional weight due to overlapping of sheets, and moisture and heat insulation

treatment, take effective thickness of the sheets as 1 mm. hence,

Dead load per meter due to sheeting on the rafter of the truss=

(4.8/0.63)x6 = 47 kg/m

5.3 Design of typical framed truss:

In this section design of typical intermediate framed truss with tubular

sections, and Pratt web pattern is carried out for clear span of 30m and 40m. The

design has been carried out with the help of STAAD Pro-2007, as per IS: 800-1984.

Since uniformly distributed load is taken on the top chord of the truss, it is designed

assuming that it is simply supported but continuous member. The effective length

factor (K) for compression member in a truss can always be conservatively taken as

equal to 1. However, due to considerable end restrains present in truss the effective

length factor (K) is generally less than 1. The maximum slenderness ratio of

compression Members has been restricted to be less than 180 and tension members to

be less than 250.

Common Data:

➢ High-Reflecting Profiled Galvalume sheet as roofing materials.

➢ Square tubular section used for purlins.

➢ Column clear height is equal to 6m.

> The framed truss is supported with pinned support at both ends.

> Brick wall as side cladding.

> The trusses are spaced at 6 m apart.

> Purlins spacing is limited to 0.77 m.

Loading

1) Dead load

Self-weight of the Framed-Truss is considered directly through the self-weight command of STAAD-pro 2007.

Dead load of roof sheeting:

The weight of 24 gauge (0.63mm thick) Galalume sheet as 4.8 kg/m2. To include the

additional weight due to overlapping of sheets, and moisture and heat insulation

treatment, take effective thickness of the sheets as 1mm. hence,

Dead load per meter due to sheeting on the rafter of the truss=

(4.8/0.63)x6 = 47 kg/m

50

= 0.47 KN/m

Due to purlins:

The square tubular pulins (50x5Ox2.9) with self weight of 4.12 kg/m, are provided at

the spacing of 0.77m. The number of purlins required for span 30m is 42, and for 40m

is 56.

Dead load per meter due to purlins on the rafter of the truss (span=30m)

42x6x4.12/30 = 34.6 kg/m

0.35 KN/m

Dead load per meter due to purlins on the rafter of the truss (span=40m)

56x6x4.12/40 = 34.6 kg/m

0.35 KN/m

2) Live load

Referring clause 4.1 of IS: 875-1984, Live load for roof membrane sheets or purlins is

0.75 kN/m2, for every degree increase in slope over 10 degrees (i.e. LL = 0.75-0.02

(Theta- 10) kN/m2). Hence,

Live load per meter on the rafter of the truss =

0.75x6 = 4.5 KN/m

3) Wind Load

For calculation of the design wind pressure, as per IS - 875 - part - III depending upon

the location of the structure, the coefficient and other parameters required can be

taken as follows,

➢ Basic wind speed for wind zone III = 44 m/sec.

➢ Basic wind speed for wind zone V = 50 m/sec.

➢ Risk coefficient K 1 = 1.0 (Cl. 5.3.1)

➢ Terrain, Height and Structure size factor K2 = 0.93 (Cl. 5.3.2)

51

➢ Topography factor K3 = 1.0 (C1.5.3.3 and Appendix — C of IS - 875 - part -

III)

➢ External pressure coefficient Cpe = -0.8p for pitched roofs (Table 5)

➢ Internal pressure coefficient Cpi = + 0.2 p for buildings with normal

permeability (Cl. 6.2.3).

Using above parameters and constants, the `equivalent load per meter on the top chord

of given truss is:

For wind speed of 44 kmph (zone III)= 7 KN/m

For wind speed of 50 kmph (zone V)= 9 KN/m

Load Combinations:

1) Dead Load + Live Load

2) Dead Load + Wind Load

52

Fig: - 5,3,3, Truss members stress ratio Fig: • 5,3,4, Truss members stress ratio

LU IQ I

Fig: - 5.3.5, Truss members stress ratio

Note: 1) LF: Load Factor; 2) Application of wind load in reverse direction, So negative sign is given to load factor

when wind is acted. 3) Allowable vertical Deflection: 125mm 4) Allowable lateral Deflection: 31mm 5) When WL is acting permissible stresses will increase by 33%. 6) The cross-sections of Fig-5.3.5, which are given in table 5.3.1, will be suitable for both 44

kmph &50 kmph, 7) Basic wind speed 44 kmph correspond to III wind zone and 5(1 kmph correspond to V

wind zone, 8) By locally strengthening the panels adjacent to column weight of Framed Truss may

further raduce,

Table. - 5.4.1, Design cross-sections and corresponding frame deflection.

*TopChord Dimensions (mm) .

Unit Deons imnsi (mm

Unit Inclined Dimensions (mm) wBotom'Chard

-

Unit ~ Unit

n Deflection Figure Weight Weight

's Weight

Vertical Dimensions (mm )=

Weight t Weight o

Remarks

(mm)

No depth thickness (Kg~m~

. width depth thicknes s ~KB/m) width depth thickness

r (Kg/m) width it hcn (Kgfm)

(Tones)

53.1 132 132 - 5,4 20.88 132 132 54 2088. .. 100 '` 100: 4 1113 60 60 26 4.55 1,61 ' 18.8 1F0.6

512 132 132 5,4 2088, 132 132 54 2088. 100 100 4 ' 11,13 60 60 26 " e 4,55 1.61 •78,3 IF 0.7,for 44kmph

5.3.3 113.5 113.5 4.8 - 15,92 - 113.5 113.5 48 1592 80 ` 80 4 9.22 60 60 2,6 455 1.37 - 83.1 LFA,6

Lf; 0.1 for 5.3.4 1135 113.5 4.8 ` 15.92 113.2 113.2 4,8 15.92 80 80 4 9.22 60 , 60 2.6 a 4,55 131 •84.6

44kmph

5.3.5 113.5 113.5 48 15,92 113.5 1135 4.8 15.92 80 F860 4 9.22 60 60" 2.6 4.55 1,31 110.4 1ft0,9,for

50kmph

Fig: -5.3.2, Truss members stress ratio Fig: -5.3.1, Truss members stress ratio

53.1 Design of Framed•Truss for 30m span:

FRAMED TRUSS @ Roof Angle 60

NODE NUMBERS

Nodal Displacement Summary

Parameters Node Horizontal

X(mm)

Vertical

Y(mm)

Resultant

(mm)

Max X 212 12.450 0.577 12,463

Min X 112 •12.450 0.577 12.463

Max Y 107 •7.471 1,298 7.583

Min Y 19 0 •83.045 83.045

Max Rst 19 0 •83.045 83.045

Table: 53.1, Frame Truss System Design Data

Span: 30m Truss height: 2.98m Truss Spacing : 6m

Number of panels ;18 Roof Angle: 60

SI,

No.

Parameter Cross-section

(mm)

Length

(m)

Weight

(kgim)

Total wt

(kg)

Remarks

I Top Chord (Rafter) 1135x113,9x4.8 30.16 15.92 148.828

2 Bottom Chord 11351113.514.8 30,34 15.92 151.11

3 Vertical web members.

60x6022,4 17.50 4.55 78.00

4 Inclined web members,

80x80x4 31,16 9.22 340.6

Column

5 Chord members 1501150x5 39.29 22.26 856.1

6 Web members 80180x4,8 26.82 10.87 285.4

Purins

7 Porbns [email protected] 50x5012,9 252 4,12 1038.24 Sag-Rod

NIL

High-Reflecting Profiled Galvalume Roofing Sheet (Min 500MPa)

$ Roof Sheet: 0,63mm 09mm+coating 4,8 kg/m1 864

Moisture Condensation + Heat Insulation Treatment

9 Glass-wool: 10mm Medium density Glass-wool panel flush with the bottom of Purlins:

Plastic sheet supported

Loads for Truss Analysis

10 Live Load (kN/m) 4,5

11 Roof Sheet (kNlm) 0.47 lmm thick

12 Purlin 0d4/m) 0.35

13 DL of Truss (kN) 13.7

FRAME TRUSS @ Roof Angle 60

NODE NUMBERS

53.2 Design of Framed-Truss for 40m span;

Nodal Displacement Summary

Parameters Node

Horizontal

X(mm)

Vertical

Y(rain)

Resultant

(nun)

Max X 214 15.017 -7.090 16.606

Min X 114 15.017 -7.089 16,606

Max Y 25 10.980 1.682 11.108

MinY 25 0 -113.9 113,893

Max Rst 25 0 -113.9 -113.9

Table. 5,33; Frame Truss System Design Data

Span: 40m Truss height: 3.70 in Truss Spacing: 6m

Number of panels : 24 Roof Angle: 60

SL

No.

Parameter Cross-section

(mm)

Length

(in)

Weight

(kg/in)

Total wt,

(kg)

Remarks

1 Top Chord (Rafter) 150X150X5 40.22 22.26 878.4

2 Bottom Chord 150X150X5 40.42 22.26 878.0

3 Vertical web members,

72X72X3.2 27.20 6.71 178.4

4 Inclined web members.

100X100X4 52.54 11.73 588.9

Column

5 Chord members 150X15018 42.53 34.38 1430.4

6 Web members 100X100X5 28.89 14.41 407.4

PurWts

7 Purlins:56 @0.77m 50z90n2,9 336 4.12 1384.32 Sag-Rod

N-R

High-Reflecting Profiled Galvalume Roofing Sheet (Min. 500MPa)

8 Roof Sheet:0.63mm 0.5mm+eoafing 4.8kglm' 864

Moisture Condensation+ Heat Insulation Treatment

9 Glass-wool: ilium Medium density Glass-wool panel flush with the bottom of Purlins

I Plastic sheet supported

Loads for Truss Analysis

10 Live Load (kNlm) 4,5

11 Roof Sheet (kNlm) 0.47 lmm thick

12 Purlin (kNlm) 0.35

13 DL of Truss (kN) 25.4

Table:- 5,3.2, Design cross-sections and corresponding frame deflection

Figure Top Chord Dimensions (mm) Unit.

Bottom Chord

Dimensions(mm) Unit Inclined Dimensions (mm) Unit Vertical Dimensions (mm) Unit

Weight Deflection

No Weight Weight Weight Weight

(Tones) ~mm~ Remarks

width depth thickness (Kg/m) width depth thickness "(Kg/m) width depth thickness (Kg/m) width depth thickness (Kg/m)

5.3.6 150 150 6 26.40 150 150 6 26.40 100 100 5 14.41 72 72 3,2 6,71 0 104.7 LF:0,6

5.3.7 150 150 6 26.40 150 150 6 26.40 100 100 5 14.41 12 72 3.2 6.71 0 -97.494 LF:-0J,for44kmph

5.3.8 150 150 5 22.26 150 150 5 22.26 100 100. 4 11,13 72 72 3.2 6,71 2.54 113.9 LF:0.6

5.3.9 150 150 5 22.26 150 150 5 22.26 100 100 4 11.73 12 72 3.2 6.71 254 -110,1 LF: -0,7, for

44kmph

5,3.10 150 150 5 22.26 150 150 5 22.26 100 100 4 11.73 12 72 3,2 6,11 2,54 .144,54 Lfc -0.9, for

SOkmph

EM

Fig: - 5.3.6, Truss members stress ratio Fig: - 5.3.7, Truss members stress ratio

Fig: - 5,3,8, Truss members stress ratio Fig: • 5.3.9, Truss members stress ratio

Note: 1) LF:LoadFactor; 2) Application of wind load in reverse direction. So negative sign is given to load factor when wind is

acted. 3) Allowable Vertical Deflection. 166 mm. 4) Allowable Lateral Deflection 31mm, 5) When WL is acting permissible stresses will increase by 33%. 6) The cross-sections of Fig-5,3,10, which are given in table 5,3.3, will be suitable for both 44 kmph &50

kmph. 7) Basic wind speed 44 kmph correspond to III wind zone, and 50 kmph correspond to V wind zone. 8) By locally strengthening the panels adjacent to column weight of Framed Truss may further raduce,

Fig: • 5.3.10, Truss members stress ratio

0.817

As the number of panels increase number of connection also increase, practically which

may cost to economy and deflection, at the same time if the number of panel is less (i.e.

more panel width) than unsupported length of the truss member increase, due which

members with higher cross section required. Which may lead to uneconomical design,

therefore the designer has to consider the above factors for deciding panel width.

In Warren web pattern the panel width is large, (i.e. nearly equal to twice of Pratt or

Howe panel width) due to which members with larger cross-sectional area is required, but

due to not having vertical web member and lesser number of connection it may lead to

overall economical truss. From fig: 5.1.9 and fig: 5.2.9 it is seen for a truss with Warren

web pattern if odd number of panels (i.e. 9 or 11 for 30m span and 13 or 15 for 40m

span) are provided the deflection control is better.

From typical design of an intermediate framed truss for an industrial roof system

with tubular sections, Pratt web pattern, and possible governing loadings the weight of

truss for 30m span is 1.37 tones and for 40m span is 2.57 tones. It has been observed that

if the panels adjacent to columns are locally strengthened the weight of the truss

frame can further be reduced.

6.3 SCOPE FOR FUTURE STUDIES:

The framed truss is commonly used structure in construction of Industrial

buildings. In present times due to large scale utilization of Pre-Engineered structures

including framed truss with tubular sections, it has imperative to further study the

behavior of the framed truss so as to provide a design more efficient than the present. The

following factors may need further study:

[1] Study on the column dimensions for varying column height under lateral loading.

[2] In present scenario, the commonly used shape of the purlins is Z & C. So a study

is required with purlin as tubular sections and their effect on purlin spacing and

effect of their connectivity with the main rafter.

[3] Interaction of framed truss as regards loads along the main axis of the building.

[4] Study of the framed truss joints with tubular sections.

61

APPENDIX-A

INTERNAL VIEW OF A SII1)

I

CLOSE UP OF A PIN-SUPPORT FOR FRAME

I. .

, _SS•

- . . -• L.J ol •.

S • - -

5) p lip

- r -

S ._P. ' • • - - -

S - -

- P. •

- •••.• - -- ,

64

i i :" /

1/ :

~~~

`~' F -1 °-rte,

vr y I ~

Typical truss with RHS

Manufacturing of Rectangular Hollow Section

65

Typical Framed truss

End Cutting Machine

x'0'0 f, mean'.

400-

— — — —,

___ __ __ () 0 Perimeter

Influence of cold-forming on yield strength for a square hollow section

X

9Of+1 ___

TandY

Ii 14 - __ Lf1

I and K K'.1'

Basic Types of joints

67

•itI'ir iIer.t for

1,2N

0 do 1r

TUN

N.

14-0

O00% N

2N sir

(e)

(g)

Example of Hollow section joint classification

A

a) Chord face h) Punchl qq shear ialwe c chord

(ci 1nvnIrd dUihti1ion, in Iho trsion hrac (d) Urvn idsIribttkn, ir. the comprosq on brace

() Shear ythnq of the choid, in the gao ) Chord Side wall failure

{g Local buckling o tie chord face

Failure mode of K and N type RHS truss joints

[4]

SELF TAPPING SCREW CONNECTING PURLIN AND ROOF SHEETING

W

EPDM WASHER (these washer are co-polymers, consisting of ethylene, propylene with proportion of diene and they offer extended life with best weather-proofing characteristics under extreme climatic condition)

SCREW GAUGE (gauge of a screw is determined by the basic of the thread outside diameter)

THREAD PITCH (thread pitch is the number of thread crests counted along a linear measurement of one inch)

IDENTIFICATION CODES of self-drilling screws is asfollows:

12 - 14 X 2.5 Screw Gauge Thread Pitch (threads Overall length of the

(Thread outside per inch) screw measured from diameter) under the head (mm) Figure -10

RIDGE-END

RIDGE PURLIN -- DSr

PURL! I Jy ( r' ® r/ r5) )\ OVERHANG AT EAVES

EAVES PURLN O /

O0 iin ri•

rF+- , EAVE-€ND f Mutwr-enay

OVERHANG AT SIDES 100 mm

LAYING OF SHEETS

70

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FRAMED- TRUSS SYSTEMS FOR LARGE SPAN INDUSTRIAL …