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UNIVERSITI TEKNOLOGI MALAYSIA

BORANG PENGESAHAN STATUS TESIS♦

JUDUL: PERFORMANCE OF STAINLESS STEEL PURLIN IN BENDING SESI PENGAJIAN: 2005 / 2006 Saya NG ZEE SUM (HURUF BESAR) mengaku membenarkan tesis (PSM / Sarjana / Doktor Falsafah)* ini disimpan di Perpustakaan

wUniversiti Teknologi Malaysia dengan syarat-syarat kegunaan seperti berikut: 1. Tesis adalah hak milik Universiti Teknologi Malaysia. 2. Perpustakaan Universiti Teknologi Malaysia dibenarkan membuat salinan untuk tujuan

aaaimapengajian sahaja. 3. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara institusi

miimmpengajian tinggi. 4. **Sila tandakan (√) (Mengandungi maklumat yang berdarjah keselamatan atau

ke kepentingan Malaysia seperti yang termaktub di dalam AKT AKTA RAHSIA RASMI 1972)

(Mengandungi maklumat TERHAD yang telah ditentukan

ole oleh organisasi/ badan di mana penyelidikan dijalankan) Disahkan oleh _____________________________________ _____________________________________

(TANDATANGAN PENULIS) (TANDATANGAN PENYELIA) Alamat Tetap: 65, LORONG WAN ZAINAL ABIDIN, TAMAN AUN SAY, PM IR. DR. MOHD. HANIM OSMAN 34000 TAIPING, PERAK. Nama Penyelia Tarikh: 5 MAY 2006 Tarikh: 5 MAY 2006

CATATAN: * Potong yang tidak berkenaan. ** Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/

organisasi berkenaan dengan menyatakan sekali sebab dan tempoh tesis ini perlu dikelaskan sebagai SULIT atau TERHAD.

♦ Tesis dimaksudkan sebagai tesis bagi Ijazah Doktor Falsafah dan Sarjana secara penyelidikan, atau disertasi bagi pengajian secara kerja kursus dan penyelidikan, atau Laporan Projek Sarjana Muda (PSM).

SULIT

TERHAD

√ TIDAK TERHAD

“I hereby declare that I have read this project and in

my opinion this project is sufficient in term of scope and

quality for the award of the degree of Master of Engineering

(Civil-Structure)”

Signature : ............................................

Name of Supervisor : PM. IR. DR. MOHD. HANIM OSMAN

Date : 5 MAY 2006

PERFORMANCE OF STAINLESS STEEL PURLIN IN BENDING

NG ZEE SUM

A project report submitted in partial fulfilment of the

requirements for the award of the degree of

Master of Engineering (Civil-Structure)

Faculty of Civil Engineering

Universiti Teknologi Malaysia

MAY 2006

ii

I declared that this project report entitled “PERFORMANCE OF STAINLESS

STEEL PURLIN IN BENDING” is the result of my own research except as cited

in references. This project has not been accepted for any degree and is not

concurrently submitted in candidature of any degree.

Signature : ............................................

Name : NG ZEE SUM

Date : 5 MAY 2006

iii

Specially dedicated to my parents, my dear dear, brother and sisters, and friends...

iv

ACKNOWLEDGEMENTS

I would like to thank all the parties who have given their co-operations and

assistance to me during the course of completing this project. First and the

foremost, I would like send my sincerest gratitude to my respectable supervisor,

Assoc. Prof. Ir. Dr. Mohd. Hanim Osman whom i would not forget particularly for

his tonnes of patience and friendliness. Without his continuous supports and

guidances, i think, i would not have see through my master project. He has set a

high standard for conduct of this study and his valuable suggestions and guidance

have provided me the motivation needed to complete this project report.

Many thanks to all the technicians in structure lab especially Encik Raja

Ezar Ishamiddin, Encik Mohd. Amiroll Mohd. Rashid, Encik Azmi Abd. Aziz,

Encik Zaaba Morap, Encik Razalee Mohammed, Encik Jafar Ahmad, and Encik

Zalaini who have contributed their practical experiences and skills in the testing

works.

I would also like thank my family and friends for their endless support and

encouragement. Their encouragement and advice are the most valuable amour

for me to push through the hard times. I would also like to acknowledge the

contributions of those who have helped either directly or indirectly in the

completion of this project.

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ABSTRACT

The results of bending test and lateral buckling test of cold formed stainless

steel purlin are presented in this dissertation. Bending test was carried out by simply

supporting purlin and loaded on its top flange, while lateral torsional buckling test

was done by using cantilevered purlin loaded at the free end of purlin. Theoretical

bending capacity of purlin was determined from BS5950 Part 5: Code of practice for

design of cold formed sections. While the buckling resistance moments were

obtained from BS5950 and from Design Manual for Structural Stainless Steel

published by European Stainless Steel Development & Information Group. From the

bending test, it was found out that the experimental moment capacities of purlin were

slightly higher than the theoretical moment capacities. However, the experimental

buckling resistance moments were significantly lower than design buckling

resistance moments. Therefore, the bending test method was considered satisfactory,

while for lateral torsional buckling test, further studies and other testing methods

were needed in order to explore verify the accuracy of cantilever method used in this

study.

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ABSTRAK

Keputusan ujian lenturan dan ujian lengkokan kilasan bagi purlin keluli tanpa

karat yang dibentuk dalam keadaan sejuk. Ujian lenturan telah dilaksana dengan

purlin disokong bebas pada kedua-dua hujungnya dan dikenakan beban pada bebibir

atas. Manakala ujian lenkokan kilasan dilaksana dengan purlin berkeadaan

tergantung dimana satu hujung diikat tegar pada tiang and satu lagi hujung bebas.

Nilai kapasiti lenturan purlin teori diperoleh berpandukan BS5950: Code of practice

for design of cold formed sections. Nilai teori keupayaan lengkokan kilasan bagi

purlin diperoleh dari BS5950 dan dari Design Manual for Structural Stainless Steel

yang diterbit oleh European Stainless Steel Development & Information Group.

Daripada ujian lenturan, didapati bahawa keupayaan lenturan purlin yang didapati

secara eksperimen adalah lebih tinggi daripada keupayaan lenturan yang diperoleh

secara teori. Walaubagaimanapun, keupayaan lengkokan kilasan yang didapati secara

eksperimen jejas lebih rendah daripada keupayaan lengkokan kilasan yang didapati

secara teori. Oleh itu, cara melaksanakan ujian lenturan dapat dianggap memuaskan.

Untuk ujian lengkokan kilasan, lebih banyak lagi kajian dan cara ujikaji diperlukan

demi menentukan tahap kebolehpercayaan kejituan cara ujikaji purlin dalam keadaan

tergantung.

vii

TABLE OF CONTENTS

CHAPTER TITLE PAGES DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES xi

LIST OF FIGURES xii

LIST OF SYMBOLS xv

LIST OF APPENDIXES xvii

1 INTRODUCTION 1

1.1 Introduction to Cold Formed Purlin 1

1.2 Advantages of Cold Formed Steel Section 3

1.3 Objectives 5

1.4 Scope of Study 6

2 LITERATURE REVIEW 7

2.1 Cold Formed-Steel 7

2.1.1 Applications of Cold Formed Steel 7

2.1.2 Manufacturing Processes 9

2.2 Stainless Steel 11

2.2.1 The Families of Stainless Steels 12

2.2.1.1 Austenitic Stainless Steels 14

2.2.1.2 Ferritic Stainless Steels 15

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2.2.1.3 Martensitic Stainless Steels 16

2.2.1.4 Duplex Stainless Steels 17

2.2.1.5 Precipitation Hardening Stainless

Steels 17

2.2.2 Characteristics of Stainless Steels 18

2.3 Design according to British Standard 5950: Part 5 18

2.3.1 Strength of Section 19

2.3.2 Effects of Cold Forming 19

2.3.3 Calculation of Section Properties 21

2.3.4 Local Buckling 21

2.3.4.1 Maximum width to thickness ratios 22

2.3.4.2 Basic Effective Width 22

2.3.4.3 Effective Widths of Plates with Both

Edges supported (stiffened elements) 25

2.3.4.4 Edge Stiffeners 26

2.3.5 Design of Members Subject to Bending 27

2.3.5.1 Determination of Moment Capacity 27

2.3.5.2 Utilization of plastic bending capacity 28

2.3.5.3 Moment Buckling Resistance 30

2.4 Design according to Design Manual for Structural

Stainless Steel 34

2.4.1 Classification of Cross Section 34

2.4.2 Effective Widths 37

2.4.2.1 Effective widths of element in Class 4

cross-sections 37

2.4.3 Design of Flexural Members 40

2.4.3.1 Yielding of Cross Section 41

2.4.3.2 Lateral Torsional Buckling 41

3 EXPERIMENTAL METHOD 46

3.1 Test Specimens 46

3.2 Coupon Test 48

3.3 Bending Test 49

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3.3.1 Experimental Method for Bending Test 49

3.3.2 Theoretical Calculation for Bending Capacity 53

3.4 Lateral Torsional Buckling Test 53

3.4.1 Experimental Method for Lateral Torsional

Buckling Test 54

3.4.2 Theoretical Method for Lateral Torsional

Buckling Test 60

3.4.2.1 Calculation Using British Standard

BS5950 (Part 5) 60

3.4.2.2 Calculation using Design Manual

for Structural Stainless Steel 61

4 RESULTS AND ANALYSIS 63

4.1 Results of Tensile Coupon Tests 63

4.2 Results of Bending Test 66

4.2.1 Experimental Bending Test 66

4.2.1.1 Results Summary of Experimental

Bending Test 67

4.2.2 Theoretical Approach to Obtain Bending Capacity 68

4.2.2.1 For Lipped Channel 160x71x16.5 (2.3mm thickness) 69 4.2.2.2 For Lipped Channel 160x71x16.5 (1.5mm thickness) 71 4.2.2.3 For Lipped Channel 160x71x16.5 (1.0mm thickness) 73 4.2.3 Comparison and Discussion of Bending Test

Results 75

4.3 Results of Lateral Torsional Buckling Test 77

4.3.1 Most Critical Load Position 77

4.3.2 Experimental Lateral Torsional Buckling Test

Results 80

4.3.3 Theoretical Approach to Obtain Buckling

Resistance Moment 84

4.3.3.1 Detailed Calculation of Resistance

Moment (Mb) Using BS5950: Part 5 85

x

4.3.3.2 Detailed Calculation of Resistance

Moment (Mb) Using Design Manual

For Structural Stainless Steel (DMSSS) 88

4.3.4 Comparison and Discussion of Lateral Torsional

Buckling Results 94

5 CONCLUSIONS 97

5.1 Summary of Study 97

5.2 Conclusions 98

5.3 Future Studies 99

REFERENCES 100

APPENDIX A 102

APPENDIX B 118

xi

LIST OF TABLES

TABLE NO. TITLE PAGES 2.1(a) Comparative Properties of stainless steel families 13

2.1(b) Comparative Properties of stainless steel families 14

2.2 Maximum width-to-thickness ratios for compression elements 35

2.3 Internal compression elements 38

2.4 Outstand compression elements 39

2.5 Values of factors C1, C2, C3 corresponding to values of factor k:

End moment loading 44

2.6 Values of factors C1, C2, C3 corresponding to values of factor k:

Tranverse loading cases 45

3.1 Specimen dimensions and types of tests conducted 47

4.1 The ultimate and yield strength of material 66

4.2 Bending capacity of purlin specimens from experiment 68

4.3 Theoretical bending capacity of different thickness 68

4.4 Comparisons of experimental and theoretical bending capacity 76

4.5 Values of buckling resistance moment obtained experimentally 80

4.6 Specimens theoretical buckling resistance moments 84

4.7 Comparison of experimental and design buckling resistance

moments 95

xii

LIST OF FIGURES

FIGURE NO. TITLE PAGES 1.1 Types of roof purlin in common use at the present 2

1.2 Roof purlin system in common use 3

2.1 Typical roll-forming sequence for a Z-section 10

2.2 Roll forming tools by stages 10

2.3 Brake press dies 11

2.4 Families of Stainless Steels 13

2.5 The Families of Austenitic Stainless Steels 15

2.6 The Families of Ferritic Stainless Steels 16

2.7 The Families of Martensitic Stainless Steels 16

2.8 The Families of Duplex Stainless Steels 17

2.9 Effective width idealization 22

2.10 K factors for uniformly compressed members 24

2.11 K factors for stiffened compression elements of beams 25

2.12 Simple lip edge stiffener 26

2.13 Single and double curvature loading 31

2.14 Restraint conditions for lateral buckling 32

2.15 Class 4 cross-section subject to bending moment 40

2.16 Class 4 cross-section subject to compression 40

3.1 General Dimension Symbols of Purlin Section 48

3.2 Tensile coupon test 49

3.3 Coupon dimension 49

3.4 Type (I) - Two point loads, restraint at two points in the

middle of the span 51

3.5 Type (II) - Four point loads, restraint at two points in the

middle of the span 51

xiii

FIGURE NO. TITLE PAGES 3.6 Type (III) - Four point loads, restraint along the span 51

3.7 Actual setup of Type I Loading and Restraining Condition 52

3.8 Actual setup of Type III Loading and Restraining Condition 52

3.9 Loading location at free end 57

3.10 Setup of lateral buckling test 57

3.11 Fixing the purlin beam rigidly to the channel column 57

3.12 Adjusting the purlin beam using the lever 57

3.13 Attaching the laser pointers to all four corners of beam 58

3.14 Fixing the transparent screen at the free end of beam 58

3.15 Testing in progress with graph paper attached on the screen 58

3.16 General setup of lateral torsional buckling test 59

3.17 Laser beam shown on the graph paper during testing 59

3.18 The component of modified laser pointers and power supply 59

3.19 Modified laser pointer circuit 60

4.1 Coupon test result for 0.8mm thick plate 64

4.2 Coupon test result for 1.0 thick plate 64



4.5 Relationship between moment and lateral displacement at

different load positions (Sample 3) 78













xiv

FIGURE NO. TITLE PAGES 4.12 Moment-lateral displacement curve for specimen no.3 81

4.13 Moment-lateral displacement curve for specimen no.4 81






xv

LIST OF SYMBOLS

An - Net area of a section

B - Width of flange

b - Overall width of an element

beff - Effective width of the stiffened plate element

beu - Effective width of the unstiffened plate element

Cb - Coefficient defining the variation of a moment on a beam

Cbx - Cb factors about x axis

Cby - Cb factors about y axis

D - Overall web depth

E - Modulus of elasticity

es - Distance between the geometric neutral axis and the effective

neutral axis of a section

fc - Applied compressive stress

Fc - Applied axial load

J - Torsion constant

H - Warping constant

Ix - Moment of inertia of a section about the x-axis

Iy - Moment of inertia of a section about the y-axis

K - Buckling coefficient

LE - Effective length of a member

L - Length of section

λLT - Equivalent slenderness

Mb - Buckling resistance moment

Mcx - Bending moment capacity about x axis in the absent of Fc and

My

Mcy - Bending moment capacity about y axis in the absent of Fc and

Mx

Mx - Applied bending moment about x axis

xvi

My - Applied bending moment about y axis

Mcr - Critical moment

ME - Eleastic lateral buckling moment of a beam

m - Equivalent uniform moment’s factor

n - Slenderness correction factor

η - Perry coefficient

γm - Material strength factor

pb - Bending strength

Pc - Buckling resistance under axial load

Pc’ - Buckling resistance under axial load for singly symmetrical

sections

pcr - Local buckling stress of an element

Pcs - Short strut capacity

PE - Elestic flexural buckling load (Euler load) for a column

po - Limiting compressive stress in a flat web

Pt - Tension capacity

py - Design strength of steel

ry - radius of gyration of section about the y axis

Sx - Plastic section modulus

t - Net material thickness

tw - Thickness of web

tf - Thickness of flange

u - Buckling parameter

x - Torsional constant

χLT - a reduction factor accounting for lateral torsional buckling

Ys - Yield strength of material

Zx - Elastic section modulus

Zeff - Effective section modulus

Zc - Compressive section modulus of the effective cross-section

xvii

LIST OF APPENDIX

APPENDIX NO. TITLE PAGES A Results from Bending Tests in Table and

Graph Format 102

B1 Graphs Used to Determine Critical Load

Locations (Raw Data) 118

B2 Graphs Used to Determine Buckling Resistance

Moment (Raw Data) 161

CHAPTER 1

INTRODUCTION

1.1 Introduction to Cold Formed Purlin

Purlin is a horizontal structural member spanning between beams or trusses to

support a roof deck. In slope glazing, purlins are the horizontal framing members.

Purlins have been used in roofing system for decades. Roof purlins account for a

substantial proportion of cold formed steel usage in buildings. Purlins are ideally

suited for production as cold rolled sections and over 60000 tonnes of cold formed

steel purlins are produced annually in United Kingdom.

There are various types of purlins available in the market; the most

commonly are Cee and Zed purlins which take the form of C and Z letter. The Zed

shape purlin was introduced from USA around 1960. Another type of purlins shape

is the Sigma shape which was introduced a few years later after the Zed shape. In

recent years the fierce competition between purlin manufacturers has led to

substantial research and development effort in the field of purlin design to produce

purlin with even greater efficiency. This has lead to further developments of the Zed

shape in particular such as Zeta shape and the UltraZED shape. All the typical shapes

of purlins are shown in Figure 1.1. Most purlins are produced from steel and most

recently galvanized steel which has a greater advantage over steel in terms of

strength. Most purlins are cold formed which means that they are formed in the cold

state from a strip of uniform thickness.

2

Figure 1.1: Types of roof purlin in common use at the present

At present, the Zed shape and its derivatives accounts for approximately two

thirds of the markets in purlins, with the other one third being accounted for by

Sigma shape. Purlin thickness used range from about 1.2 mm to 3.2 mm and material

of yield strength of 350 N/mm2 is commonly used in the production of purlins.

A variety of different purlin systems are also available to enable the designer

to exercise a choice between simple inexpensive and easy to erect systems or more

complex but more efficient systems. The main systems in use today are shown in

Figure 1.2. Figure 1.2(a) shows the simple non-continuous system in which the

purlins are more or less simply supported at each rafter. Figure 1.2(b) shows the

double spanning system in which the purlins span continuously over a central rafter.

This system is generally stronger and much less flexible than the non-continuous

system, but is subject to some restrictions on the lengths of double spanning purlins

which can be transported. Figure 1.2(c) shows the sleeved system in which purlins

are jointed at alternate rafters by semi-rigid sleeve connections, with the sleeves

being, in most cases, of the same cross-section as the purlin. This system is most

widely used at the present moment. Of the sleeves are designed correctly the ideal

moment distribution can be obtained due to the moment redistribution capabilities of

the semi-rigid connections. In the overlap system, Figure 1.2(d), the purlins are

“overlapped” at each rafter to provide double the strength at the supports. This

system gives the best performance, but necessitates care in erection and the use of

end purlins of different thickness to interior purlins.

Zed Sigma Zeta Ultra Zed Cee

3

Figure 1.2: Roof purlin system in common use

While steel and galvanized steel are common material in purlin, there is

another less popular material that can be used in purlin production which is stainless

steel. Until now, little has been studied about the behavior of cold formed stainless

steel purlin. The focus of research is to study the behavior of stainless steel Cee-

purlin using experimental method, and to produce a draft design guide for stainless

steel Cee-purlin.

1.2 Advantages of Cold Formed Steel Section

Generally, cold formed steel sections have several advantages over hot rolled

steel sections, timber sections and concrete. The main advantages are listed as

follows:

1. No insect and fungal infection: The problems such as rotten or decomposed

due to insect and fungal infection are eliminated, therefore the material curing and

maintenance costs which is necessary for the timber and concrete construction could

also be eliminated.

4

2. Consistency and accuracy of profile: The nature of the manufacturing process

– cold rolling – enables the desired profile to be maintained and repeated for as long

as it required, in a very close tolerances. Moreover, the very little tool wear and the

cold rolling process is ideally suited to computerized operation which assists to the

maintenance of accuracy.

3. Versatility of profile shape: Almost any desired cross-sectional shape can

be produced by cold rolling.

4. It could be pre-galvanized or pre-coated: The steel material may be

galvanized or coated by plastic materials either to enhance its resistance to corrosion

or as an attractive surface finish.

5. Variety of connection and jointing methods: All conventional methods of

connecting components, e.g. riveting, bolting, welding, and adhesives are suitable for

cold formed section.

6. Speedy in construction, and suit for site erection: Generally the steel

construction has eliminated the curing time which is unavoidable in concrete

construction; therefore cold formed steel construction in certain parts of a structure is

far faster than concrete construction. The cold formed steel may have an edge over

hot rolled steel since it can be easily be cut and erected with very light machine or

manually.

7. Increase in yield strength due to cold forming: The cold forming process

introduces local work hardening in the strip being formed in the vicinity of the

formed corners. This local work hardening may results in an increment of ultimate

yield strength to about 25% from its virgin strength.

8. Minimization of material usage: Since the material used can be very thin in

comparison with the lower thickness limits of hot rolled steel sections, it allows the

material usage for a given strength or stiffness requirement to be much less than that

of the smallest hot rolled sections. The material thickness, or even the cross-sectional

5

geometries could be controlled to achieve the structural features with minimum

material weight.

9. High profitability: In cold rolled process, the manufacturing cists of cold

rolled steel section mainly involve the initial modal of purchasing the rolling

machine and the costs of steel strip material later. The machinery cost is only needed

once, then the cost can be recovered back from the continuous production. The cold

formed purlin normally used for roof building purposes involves only simple and fast

erection with light erection tools, therefore it is gaining the preference of local

constractors and fabricators since the investment is little and the profits return is

faster than other constructional parts.

1.3 Objectives

The objectives of this research are as follows:

i) To develop experimental method to study the behavior of Lipped Channel

sections subjected to moment and lateral torsional buckling moment.

ii) To obtain experimental data of section and member capacities of the

stainless steel purlin subjected to flexural load (bending and lateral

torsional buckling)

iii) To analyze the results of the test in comparison with the design capacity

according to relevance standard reference based on the tested yield

strength of the materials.

6

1.4 Scope of Study

The scope of study will cover both the experimental and theoretical

investigation of stainless steel cold formed lipped channel (Cee Purlin) subjected to

bending moment and lateral torsional buckling moment. The size ranges of purlin

samples tested are of thickness from 1.0 to 2.7mm, width of 71 mm, depth of 160

mm and lip depth of 16.5 mm. The scopes of study in this research are:

i) Determination of the design yield strength of stainless steel of purlin

sections using tensile coupon test.

ii) Determination of the ultimate moment capacity of stainless steel lipped

channel experimentally* and theoretically**.

iii) Stainless steel lipped channel are tested in simply supported condition for

bending failure.

iv) Determination of the buckling resistance moment, Mb of stainless steel

lipped channel experimentally* and theoretically**.

v) Stainless steel lipped channel are tested in cantilevered condition for

lateral torsional buckling failure.

vi) To study the behavior of stainless steel lipped channel under the effects of

lateral torsional buckling experimentally* (most critical load point,

torsional profile).

* Conducted in the structural laboratory of civil engineering faculty, UTM

** Based on BS5950 - Part 5: Code of Practice For the Design of Cold Formed Sections and

Design Manual for Structural Stainless Steel by European stainless steel development &

information group.

CHAPTER 2

LITERATURE REVIEW

2.1 Cold Formed-Steel

Cold formed steel products are used in all aspects of modern life. Besides

being used as structural members, cold formed steel are also used in automobile

bodies, kitchen appliances, furniture, corrugated sheets for farm buildings,

corrugated culverts, round grain bins, retaining walls, rails and many other uses.

With the help of cold forming processes, cold formed steel products come with a

diversity of shapes, sizes and applications. Cold formed steel for industrial and

commercial buildings began about mid-20th century, and widespread usage of cold

formed steel in residential buildings only started in the 1980s.

2.1.1 Applications of Cold Formed Steel

Cold formed steel structural members are normally used in the following

applications:

i) Roof and wall systems of industrial, commercial and agricultural buildings

Typical sections for use in roof and wall systems are Z- (zee) or C- (channel)

sections, used as purlins and girts, or sometimes beams and columns. Typically,

formed steel sheathing or decking spans across these members and is fastened to

8

them with self-drilling screws through the “valley” of the deck. In most cases, glass

fiber insulation is sandwiched between the deck and the purlins or girts.

ii) Steel racks for supporting storage pallets

The uprights are usually channels with or without additional rear flanges, or

tubular sections. Tubular or pseudotubular sections such as lipped channels

intermittently welded toe-to-toe are normally used as pallet beams. In the United

States the braces are usually welded to the uprights, whereas in Europe, the braces

are normally bolted to the uprights.

iii) Structural members for plane and space trusses

Typical members are circular, square, or rectangular hollow sections both as

chords and webs, usually with welded joints. Bolted joints can also be achieved by

bolting onto splice plates welded to the tubular sections. Channel section chord

members can also be used with tubular braces bolted or welded into the open

sections. Cold formed channel and Z sections are commonly used for the chord

members of roof trusses of steel-fromed houding, Trusses can also be fabricated from

cold-formed angles.

iv) Frameless stressed-skin structures

Corrugated sheets or sheeting profiles with stiffened edges are used ti form

small structures up to a 30-ft clear span with no interior framework. Form buildings,

storage sheds, and grain bins are typical applications.

v) Residential framing

Lipped and unlipped channels, made to the same dimensions as nominal 2 x

4s are typically used in the walls of residential buildings. Larger channel sections are

used as floor and ceiling joists, and roof trusses are commonly made of small channel

sections screwed or bolted together.

vi) Steel floor and roof deck

Formed steel deck is laid across steel beams to provide a safe working

platform and a form for concrete. It is normally designated as a wide rib,

intermediate rib, or narrow rib deck. Some deck types have a flat sheet attached to

9

the bottom of the ribs which creates hollow cells providing raceways for electrical

and other cables. This bottom sheet may be perforated for an acoustical ceiling.

Some decks have embossments in the sloping sides of the rib that engage the

concrete slab as a kind of shear key and permit the deck to act compositely with the

concrete.

vii) Cold-formed tubular members

Hollow structural sections (HSS) may be made by cold-rolling to produce a

round, which is then closed by electric resistance welding (ERW). The round shape

can then be used as is or further formed into a square or rectangular.

2.1.2 Manufacturing Processes

Cold-formed members are usually manufactured by one of two processes

which are roll forming and brake forming.

Roll forming consists of feeding a continuous steel strip through a series of

opposing rolls to progressively deform the steel plastically to form the desired shape.

Each pair of rolls produces a fixed amount of deformation in a sequence of the type

shown in Figure 2.1. For example, a Z section is formed by first developing the

bends to form the flanges. Each pair of opposing rolls is called a stage, as shown in

Figure 2.2. In general, the more complex the cross-sectional shape, the greater the

number of stages that required.

Brake forming involves producing one complete fold at a time along the full

length of the section, using a machine called as press brake such as one shown in

Figure 2.3. For sections with several folds, it is necessary to move the steel plate in

the press and to repeat the braking operation several times. The completed section is

then removed from the press and a new piece of plate is inserted for manufacturing

of the next section.

10

Roll forming is the more popular process for producing large quantities of a

given shape. The initial tooling costs are high, but the subsequent labor content is

low. Press braking is normally used for low-volume production where a variety of

shapes are required and the roll-forming tooling costs cannot be justified. Press

braking has the further limitation that it is difficult to produce continuous lengths

exceeding 20ft.

A significant limitation of roll forming is the time it takes to change rolls for

a different size section, Consequently, adjustable rolls are often used which allow a

rapid change to a different section width or depth. Roll forming may produce a

different set of residual stresses in the section when compared with braking, so the

section strength may be different in cases where buckling and yielding interact. In

addition, corner radii tend to be much larger in roll-formed sections, and this can

affect structural actions such as web crippling.

Figure 2.1: Typical roll-forming sequence for a Z-section

Figure 2.2: Roll forming tools by stages

Stage 1

Stage 2

Stage 3

Stage 4

Stage 5

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