A COMPARISON BETWEEN EUROCODE 3 (1992) AND BRITISH STANDARD 5950 (2000) FOR FLEXURAL MEMBER DESIGN

FRANKY ANAK AJIE

..

This project is submitted in partial fulfil1ment of . the requirements for the degree of Bachelor of Engineering with Honours

(Civil Engineering)

,.• Faculty of Engineering UNIVERSITY MALAYSIA SARA WAK

2006

I

To my beloved parents, Ajie Anak Lang and Ungo Anak Bilong

•

11

ACKNOWLEDGEMENT

.,'"

The following people have made significant contributions to the writing of this

project and their assistance is acknowledged with grateful thank.

The author is grateful to thesis supervisor, Puan Azida Rashidi for her guidance

and advices throughout the project.

Not forget also to thank the author's parents, Ajie Anak Lang and Ungo Anak

Bilong who give financial support until the completion of the project.

Finally, thanks once again to everyone who has helped in contributing ideas and

advices throughout the entire project. Thank you very much .

11l I

ABSTRACT

The European Standards and British Standards are the standards used in design of

structural steeL This project is about the comparisons between the two standards

with respect to a flexural member design. The European Standards used for this

project is the Eurocode 3: Part 1.1 (1992) or simply written as EC 3: Part 1.1

(1992). While, the British Standards used in this project is the BS 5950: Part 1

(2000). There are few methods of comparison used in this project. These methods

include the notation, load factors, load combinations and design considerations, an

example of flexural member design, the safety factors, economical factors,

advantages and disadvantages of the two standards. Throughout the project, it is

found that the notations used are slightly different from each standard. The limit

states design is the design basis for both standards. The factors considered in

flexural member design include shear capacity, bending moment capacity, web

buckling capacity, web bearing capacity or web crushing capacity and deflection.

For the EC 3: Part 1.1 (1992), an extra check on web crippling and maximum

deflection, ornax which is not required in the BS 5950: Part 1 (2000). From the

results, it can be concluded that the EC 3: Part 1.1 (1992) is more conservative

while the BS 5950: Part 1 (2000) is more economical. However, in the real

practice, both of the standards offer almost the same results in term of

conservativeness and economical factor.

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ABSTRAK

European Standards dan British Standards merupakan piawaian yang

digunakan untuk merekabentuk struktur binaan. Projek ini membincangkan

perbezaan di antara kedua-dua piawaan dengan merekabentuk angota lenturan.

European Standards yang digunakan dalam projek ini ialah Eurocode 3: Part 1.1

(1992) atau ringkasnya ditulis sebagai EC 3: Part 1.1 (1992). Manakala British

Standards yang digunakan dalam project ini ialah BS 5950: Part 1 (2000).

Beberapa kaedah telah digunakan dalam projek ini. Ini termasuklah perbandingan

simbol-simbol yang digunakan, perbandingan faktor beban, perbandingan

gabungan factor beban dan pertimbangan merekabentuk, perbandingan

menggunakan contoh merekabentuk angota lenturan, perbandingan dari segi

faktor keselamatan, faktor economi dan perbandingan kebaikan and keburukan

antara kedua-dua piawaian tersebut. Melalui projek ini, diketahui bahawa

kebanyakan simbol-simbol yang digunakan dalam kedua-dua piawaian agak

berlainan antara satu sarna lain. Rekabentuk keadaan had muktamad dan had

khidmad merupakan dasar rekabentuk untuk kedua-dua piawaian. Faktor-faktor

yang dipertimbangkan dalam angota lenturan termasuk keupayaan ricih,

keupayaan lenturan, web buckling capacity, web bearing capacity atau web

crushing capacity dan pesongan. Untuk EC 3: Part /.1 (1992) semakan tambahan

ke atas web crippling dan pesongan maximum, omax perlu dilakukan, semakan ini

tidak diperlukan di dalam BS 5950: Part 1 (2000). Daripada keputusan yang

diperolehi, dapat disimpulkan bahawa EC 3: Part 1.1 (1992) lebih konservatif

manakala BS 5950: Part 1 (2000) lebih jimat dari segi ekonomi. Walau

bagaimanapun, dalam situasi sebenar, kedua-dua piawai akan memberikan

keputusan yang hampir sama dari segi factor konservatif and ekonomi.

.",

v

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TABLE OF CONTENT

Page

TITLE i

DEDICATION ii

ACKNOWLEDGEMENT iii

ABSTRACT iv

ABSTRAK v

TABLE OF CONTENT vi-ix

LIST OF FIGURES x

LIST OF TABLES xi-xii

LIST OF SYMBOLS xiii-xviii

LIST OF ABBREVIATION xix

Chapter 1 INTRODUCTION

1.1 Background 1-3

'- 1.2 Significance of Study 4

1.3 Aim and Objective 5

.... 1.4 Scope of Study, 6

1.5 Conclusion 6

VI

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Chapter 2 LITERATURE REVIEW

2.1 Introduction 7

2.2 The Standards 7

2.2.1 European Standard - EC 3: Part 1.1 (1992) 8

2.2.2 British Standard - BS 5950: Part 1 (2000) 8

2.3 Structure Design Basis 8

2.3.1 Load Factors and Combinations for the EC 3: Part 1.1 (1992) 10-11

2.3.2 Load Factors and Combinations for the BS 5950: Part 1 (2000) 12 -13

2.4 Partial Safety Factors for materials 13

2.4.1 Partial Safety Factors for materials for the EC 3: Part 1.1 (1992) 13-14

2.4.2 Partial Safety Factors for materials for the BS 5950: Part 1 (2000) 14

2.5 Flexural Member Design Consideration 14

2.5.1 Flexural Member Design Consideration for the EC 3: Part 1.1 (1992) 15-24

2.5.1 Flexural Member Design Consideration for the BS 5950: Part 1 (2000) 25-34

2.6 Conclusion 35

Chapter 3 METHODOLOGY

3.1 Introduction 36

3.2 Methods of comparison 36 ... 3.2.1 Notation 36

3.2.2 Load factors, load combinations and

Vll

Chapter 4

Chapter 5

.... !

design consideration

3.2.3 A case study of flexural member design

3.2.4 The safety factors, economical factors, advantages and disadvantages of the two standards

3.4 Conclusion

DESIGN EXAMPLES

4.1 Introduction

4.2 Design examples

4.3 Design using EC 3: Part 1.1 (1992) for simply supported restrained beam

4.4 Design using BS 5950: Part 1 (2000) for simply supported restrained beam

4.5 Design using EC 3: Part 1.1 (1992) for simply supported unrestrained beam

4.6 Design using BS 5950: Part 1 (2000) for simply supported unrestrained beam

4.7 Conclusion

RESULTS AND DISCUSSION

5.1 Introduction

5.2 Terminology

5.2.1 Decimal Point

5.2.2 Actions

5.2.3 Resistance

5.2.4 Subscripts

5.2.5 Design Philosophy

37

37-39

40

40

41

41-42

43-52

53-62

63-72

73-81

82

83

83

84

84

85

85

86

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Chapter 6

.. ,

5.2.6 Partial Load Factors 86

5.2.7 Load Factors and combination 87-90

5.2.8 Partial Safety Factors 91-92

5.3 Symbols 92-93

5.4 Conventions 93-94

5.5 Material and Elastic Modulus 94-96

5.6 Limiting shear stress and limiting shear capacity 96-98

5.7 Summary of results obtained from Chapter 4 98-99

5.8 Conclusion 100

CONCLUSIONS AND RECOMMENDATIONS

6.1 Introduction 101

6.2 Problems Faced 101

6.3 Conclusion 102-104

6.4 Recommendations 105

REFERENCES 107-108

APPENDIX A 109-116

APPENDIXB 116-122

APPENDIXC 123

APPENDIXD 124-125

IX I

,..... ... e

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Figures

2.1

3.1

5.1

5.2

5.3

5.4

5.5

5.6

LIST OF FIGURES

Pages

Vertical Deflection 24

Simply Supported Beam 38

Actual load consist ofdead load and imposed load. 88

Actual load consist ofdead load and wind load 89

Actual load consist ofdead load, imposed load and 90 wind load.

Comparison ofmembers axes between EC 3: Part 1.1 (1992) 94 and BS 5950: Part 1 (2000)

Limiting shear stress 97

Limiting shear capacity 97

x

I

Tables

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

5.1

5.2 'I':,

5.3

• 5.4

5.5

LIST OF TABLES

Pages

Limit States - BS 5950: Part: 1 (2000) 9

Design value of action for use in the combination of actions 11

Partial safety factors for actions on building structures for 11 persistent and transient design situations.

Partial factors for loads, 'Yf 12

Maximum width - to - thickness ratios for compression elements 15

Recommended limiting values for vertical deflection. 23

Classification of cross section 25

Limiting width to thickness ratios 26

Limits for calculated deflection 34

Comparison in term of decimal point 84

Comparison in term of action is called in the two standards 84

Comparison in term ofresistance is called in the two codes 85

Partial Load Factors 87

Partial Safety Factors for materials, EC 3: Part 1.1 (1992) 91

Xl

i

5.6 Partial Safety Factors for materials, BS 5950: Part 1 (2000) 91

5.7 Symbols used in the EC 3: Part 1.1 (1992) and 93 BS 5950: Part 1 (2000)

5.8 Comparison of shear capacity 96

5.9 Summary of Design - Total design loads 98

5.10 Summary of Design Shear Capacity 98

5.11 Summary of Design - Bending Moment 99

5.12 Summary of Design - Bearing Capacity 99

5.13 Summary ofDesign Deflection 99

XlI

p AX i¢

LIST OF SYMBOLS

Symbols used in this project - EC 3: Part 1.1 (1992)

Latin upper case letters

A -Accidental action

A - Area

C - Capacity; Fixed value; Factor

E - Modulus of elasticity

F - Action

F - Force

G - Pennanent action

G - Shear modulus

I - Second moment of area

K - Stiffness factor (l/L)

L - Length; Span; System length

M - Moment in general

M - Bending moment

N - Axial force

Q - Variable action

R - Resistance; Reaction

S -Internal forces and moments (with subscripts d or k)

S - Stiffness (shear, rotational ... stiffness with subscripts v, j ...)

T - Torsional moment; Temperature

V - Shear force; Total vertical load or reaction ;Ilf:,

W - Section modulus

Latin lower case letters

a-Distance; Geometrical data

a -Area ratio

Xlll I

--- --..,.....-­

b -Width; Breadth

c -Distance; Outstand

d -Diameter; Depth; Length of diagonal

e -Eccentricity

e -Edge distance; End distance

f -Strength (of a material)

h -Height

-Radius of gyration

k -Coefficient; Factor

-(or I or L) Length; Span; Buckling lengtha

a J (lower case L) can be replaced by L or by = (handwritten) for certain lengths or to avoid confusion with I (numeral) or I (upper case i)

n -Ratio ofnormal forces or normal stresses

p -Pitch; Spacing

q -Uniformly distributed force

r -Radius; Root radius

s -Staggered pitch; Distance

t -Thickness

xx -Axis along member

yy -Axis of cross-section

zz -Axis of cross-section

Greek lower case letters

a -(alpha) Angle; Ratio; Factor

y -(gamma) Partial safety factor; Ratio

o -(delta) Deflection; Deformation

-(epsilon) Strain; Coefficient [235/fy)O,5 (fy in N/mm2)

-(eta) Coefficient (in Annex E)

-(lambda) Slenderness ratio; Ratio

-emu) Slip factor; Factor

v -(nu) Poisson's ratio

p -(rho) Reduction factor; Unit mass

XIV

a -(sigma) Nonnal stress

't -(tau) Shear stress

¢ -(phi) Rotation; Slope; Ratio

X -(chi) Reduction factor (for buckling)

\jI -(psi) Stress ratio; Reduction factor or Factors defining representative

values ofvariable actions.

Subscripts

A

a

b

C

c

cr

d

E

eff

e

el

f

g

G

h

h

i, j, k

~" k

I

LT

Mr M

m

-Accidental; Area

-Average (yield strength)

-Bearing; Buckling

-Capacity; Consequences

-Cross section

-Critical

-Design; Diagonal

-Euler

-Effective

-Effective (with further subscript)

-Elastic

-Flange; Fastener

-Gross

-Pennanent action

-Height; Higher

-Horizontal

-Inner

-Indices (replace by numeral)

-Characteristic

-Lower

-Lateral-torsional

-Material

-(Allowing for) bending moment

-Bending

xv

max

mm

N

pI

Q

R

s

V

x

y

Y

z

-Maximum

-Minimum

-(Allowing for) axial force

-Plastic

-Variable action

-Resistance

-Stiff; Stiffener

-(Allowing for) shear force

-Axis along member; Extension

-Yield

-Axis of cross-section

-Axis of cross-section

XVl

l

,... ,

Symbols used in this project - BS 5950: Part 1 (2000)

A -Area

Ae -Effective net area

AetT -Effective cross-sectional area

Av -Shear area of a member

a -Spacing of transverse stiffeners

B -Width

b -Outstand

D -Depth of section or Diameter of section

d -Depth ofweb

E -Modulus of elasticity of steel

e -Edge or end distance

Fv -Shear force in a member

fc -Compressive stress due to axial force

fv -Shear stress

H -Warping constant of section

h -Height

Ixx -Second moment ofarea about the major axis

Iyy -Second moment of area about the minor axis

J -Torsion constant of section

L -Length or Span

LE -Effective length

M -Moment

Mb -Buckling resistance moment (lateral-torsional buckling)

Me -Moment capacity

m -Equivalent uniform moment factor

Pc -Compression resistance

P v -Shear capacity of a member

Pb -Bending strength (lateral-torsional buckling)

Pc -Compressive strength

py -Design strength ofsteel

qw -Shear buckling strength of a web

XVll

" p

rx -Radius of gyration about the major axis

ry -Radius of gyration about the minor axis

Seff -Effective plastic modulus

Sx -Plastic modulus about the major axis

Sy -Plastic modulus about the minor axis

T -Thickness of a flange

t -Thickness or Thickness of a web

u -Buckling parameter of a cross-section

Vb -Shear buckling resistance of a web

Vcr -Critical shear buckling resistance of a web

v -Slenderness factor for a beam

x-Torsional index of a cross-section

Zeff -Effective section modulus

Zx -Section modulus about the major axis (minimum value unless otherwise

stated)

Zy -Section modulus about the minor axis (minimum value unless otherwise

stated)

'Yf -Overall load factor

e -Constant (275/py)O.5

J... -Slenderness, i.e. the effective length divided by the radius of gyration

Acr -Elastic critical load factor

ALO -Limiting equivalent slenderness (lateral-torsional buckling)

ALI -Equivalent slenderness (lateral-torsional buckling)

AO -Limiting slenderness (axial compression)

XVlll

I

LIST OF ABBREVIATION

AL - Actual load

AM - Allowable moment

AS Allowable shear

ASD Allowable strength design

AW - Allowable web

BS - British standard

CIDB Construction Industry Development Board

DL Design Load

DM - Design Moment

DS - Design Shear

DW -Design Web

LFC - Load Factor and Combination

LRFD - Load and resistance factor design

LSD - Limit state design

MC - Moment Capacity

NARB- National Association ofRome Builders

RF - Reduction Factor

SC Shear Capacity

WC - Web Capacity

XIX

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CHAPTERl

INTRODUCTION

1.1 Background

Steel is one of the principle materials used in designing buildings and civil

engineering works such as bridges and towers. There are five types of structural

steelwork that are widely used in the construction of buildings and civil

engineering works. These are carbon steels, alloy steels, high-strength low-alloy

steels, stainless steels and tools steels. Each types of steel exhibits different

characteristics such as strength, ductility, hardness, and corrosion resistance.

Steels are usually more economical, recyclable, long life, easy to transport and

handle on site.

There are several steel standards used all over the world, such as the

American Iron and Steel Institute Standards, Australian and New Zealand

Standards, Japanese Standards, British Standards and European Standards or

Eurocodes. In this project work, the Eurocodes and British Standards will be used.

The Eurocodes are the European Standards applied in designing of structural

design. The European Standards that will be used for this project work is the

l I

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Eurocode 3 (1992) or simply written as EC 3 (1992). It applies to the design of

buildings and civil engineering works in steeL This standard came into effect on

15 November 1992 and was published by the European Committee for

Standardization (CEN) and the National Application Document (NAD) to be used

with the European Pre-Standard (ENV) for the design of buildings to be

constructed in the United Kingdom. Like the BS 5950 (2000), EC 3 (1992) comes

in a number of parts and covers a range of application. It consists of the following

Parts:

Part 1.1: General rules and rules for buildings.

Part 1.2: Fire resistance.

Part 1.3: Cold formed thin gauge members and sheeting.

Part 2 : Bridges and plated structures.

Part 3 : Towers, masts and chimneys.

Part 4 : Tanks, silos and pipelines.

Part 5 : Piling.

Part 6 : Cranes structures.

Part 7 : Marine and maritime structures.

Part 8 : Agricultural structures.

Part 1.1 of EC 3 (1992) gives a general basis for the design of buildings and

civil engineering works in steel. The remaining Parts of the code (Part 1.2 to Part

8) are generally related to specifications or to specialist types of construction and

will not be mentioned further in this project work.

2

p

The British Standards for steel that will be used in this project work is the BS

5950 (2000). It is the principal source of guidance for the design of structural

steelwork in the United Kingdom and is widely used in Malaysia. This standard

has been prepared under the direction of the Civil Engineering and Building

Structures Standards Policy Committee and was published under the authority of

the Standard Committee B/525/31 in May 2001. It replaces the BS 5950 (1990)

which is withdrawn. BS 5950 (2000) edition introduces technical changes based

on the review of the BS 5950 (1990). BS 5950 (2000) comprise of the following

Parts:

Part 1: Code of practice for design: Rolled and welded sections.

Part 2: Specification for materials, fabrication and erection: Rolled and

welded sections.

Part 3: Design in composite construction Section 3.1: Code of practice for

design of simple and continuous composite beams.

Part 4: Code of practice for design of composite slabs with profiled steel

sheeting.

Part 5: Code of practice for design of cold formed thin gauge sections.

Part 6: Code of practice for design of light gauge profiled steel sheeting.

Part 7: Specification for materials, fabrication and erection: Cold formed

sections and sheeting.

Part 8: Code of practice for fire resistant design.

Part 9: Code of practice for stressed skin design.

3

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,.......-------------------~----~~~-~FP

,!

BS 5950 (2000): Part 1 gives recommendations for the design of simple and

continuous steel structures, using rolled and welded sections. The remaining Parts

of the code (Part 2 to Part 9) are generally related to specifications or to specialist

types of construction and will not be mentioned further in this project work.

In this project work, the comparison is made between the EC 3: Part 1.1

(1992) and BS 5950: Part 1 (2000). The flexural member design is taken as an

example of calculation to show the differences. The scopes of the comparison will

be discussed further in Section 1.4 of this chapter.

1.2 Significance of study

According to a journal by Sooi and Teoh (2004), the EC 3 (1992) will

replace BS 5950 (2000) in the year 2008 in the United Kingdom. It is envisioned

that the process of transition from the usage of BS 5950 (2000) to EC 3 (1992) in

Malaysia will run parallel with that in the United Kingdom.

The adoption of EC 3 (1992) could help the local construction industry and

practicing engineers in gaining access to the latest technology in steel engineering

practices. They could also be able to get updates since the EC 3 (1992) documents

would have regular maintenance. Another advantage in adopting EC 3 (1992) is

its ready alignment with International Standards Organization or ISO, in term of

4

pit

format and coverage. EC 3 (1992) has unique features, such as National Annexes,

formally referred to as National Application Documents (NAD).

As Malaysia always uses British Standards as the main resource of reference

and since the British has decided to align with the European Union with the

adoption of EC 3 (1992), it would be prudent for Malaysia to follow suit.

1.3 Aim and objectives

The aim of this project work is to alleviate the learning curve through the

comparison of the design approaches and the parametric studies of the two

standards. This will ensure a smooth and easier transition of the BS 5950 (2000)

to the EC 3: (1992).

Thus, the objectives are:

(a) To compare the notations, limit state design and design considerations

between the two standards.

(b) To show the simplified design method ofEC 3: Part 1.1 (1992).,

I i I

(c) To show the simplified design method ofBS 5950: Part 1 (2000).

'<\'.0

l I (d) To compare the design methods for flexural member design between

the two standards.

(e) To determine the advantages and disadvantages of each standards.

I (f) To compare the safety and economy aspects between the two standards

by using an example of flexural member design as a case study.

5

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1.4 Scopes of study

This study is limited to:

(a) The Ee 3 Part 1.1 (1992) and BS 5950 Part 1 (2000).

(b) Only the flexural member design is considered as a case study.

(c) The ultimate limit state and serviceability limit state only.

(d) Only hot-rolled steel member is considered.

1.5 Conclusion

Hence, it is very important for local construction industry and practicing

engineer to understand the significance of the transition of BS 5950 (2000) to Ee

3 (1992). This will help our local construction industry and practicing engineers to

get equipped and ready to the adoption of the Ee 3 (1992) in the year 2008. In the

next chapters, we will discuss more detail about the Ee 3: Part 1.1 (1992) and the

BS 5950: Part 1 (2000).

6

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

This chapter describes about the EC 3: Part 1.1 (1992) and BS 5950: Partl

(2000) in general. It highlights the differences between the two standards based on

design basis and member design considerations with respect to flexural member

design.

2.2 The standards

As mentioned earlier in Section 1.1 of Chapter 1, there are many standards

for the design of structural steel all over the world. Thus, in this project work, the

comparison between the EC 3: Part 1.1 (1992) and the BS 5950: Partl (2000) for

t flexural member design will be studied.

I I

I I i 7

l i

2.2.1 European Standard - EC3: Part 1.1 (1992)

The European Standard used in this project work is EC 3: Part 1.1 (1992). It

gives a general basis for the design of buildings and civil engineering works in

steel. This standard is published by the European Committee for Standardization

(CEN) and the National Application Document (NAD) and come into effect on 15

November 2000. It is to be used with the European Pre-Standard (ENV) for the

design of buildings to be constructed in the United Kingdom.

2.2.2 British Standard - BS 5950: Part 1 (2000)

The British Standard used in this project work is BS 5950: Part 1 (2000).

This standard has been prepared under the direction of the Civil Engineering and

Building Structures Standards Policy Committee and was published under the

authority of the Standard Committee B/525/31 in May 2001. It replaces the BS

5950: Part 1 (1990) which is now withdrawn. BS 5950: Part 1 (2000) gives

recommendations for the design of simple and continues steel structures using

rolled and welded sections.

2.3 Standards Design Basis

The design basis in structural steel design is based on the limit states concept.

This design basis is used in both of the standards, EC 3: Part 1.1 (1992) and BS

5950: Part 1 (2000).

8

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According to Clause 2.1.3 BS 5950: Part 1 (2000), structures should be

designed by considering the limit states beyond which they would become unfit

for their intended use. There are two types of limit states to be taken into account

in the limit states design, ultimate limit states and serviceability limit states.

According to the BS 5950: Part 1 (2000), ultimate limit states concern the safety

of the whole or part of the structure while serviceability limit states correspond to

limits beyond which specified service criteria are no longer met.

Therefore, the design is done based on the strength and stability at ultimate

loading. After the design was done, the deflection will be checked under the

serviceability loading. Table 2.1 outlines the typical limit states appropriate to

steel structures.

Table 2.1: Limit States

Ultimate limit states (ULS) Serviceability limit states (SLS) Strength (including yielding, rapture, Deflection.

buckling and forming a mechanism).

Stability against overturning and sway . Vibration.

stability.

Fracture due to fatigue. Wind induced oscillation.

IBrittle fracture. I Durability.

[Source: BS5950: Part 1 (2000)]

In a flexural member design, factors such as material strength loading and

structural performance will be taken into account. For analysis purposes, partial

load factors should be applied to the working or nominal loads of dead load,

9

imposed load and wind load in order to minimize the failure of the structures.

These factors are applied based on the load factors and combinations. The load

factors and combinations of the two standards will be discussed further in Section

2.3.1 and Section 2.3.2 for the EC 3: Part 1.1 (1992) and the BS 5950: Part 1

(2000) respectively.

2.3.1 Load Factors and Combinations for the EC 3: Part 1.1 (1992)

The Eurocode provides indicative values for various safety factors and are

shown in the text as "boxed values" 1.35

According to Chanakya Arya (1994), the values in the box D signify

that these values may be used by individual member state for time being. This

system of identifying certain parameters was introduced in order to account for

national differences in material properties, design and construction practices and

climatic condition.

According to Clause 2.3.2.2 of EC 3: Part 1.1 (1992), load factors and

combinations are taken as shown in Table 2.2.

10

I

r Table 2.2: Design values of actions for use in the combination of actions

[Source: EC 3: Part 1.1 (1992)]

To obtain the persistent and transient design situations, Clause 2.3.3 ofEC 3:

Part 1.1 (1992) shall follow. Table 2.3 below shows the partial safety factors for

actions on building structures for persistent and transient design situations.

For unfavourable effect, the permanent actions is multiplied by 1,35 and

variable actions is multiplied by 1,5.

Table 2.3: Partial safety factors for actions on building structures for persistent and transient design situations.

Permanent Variable actions Qd Accidental IDesign I situation actions Gd Leading Accompanying actions Ad Ii

I variable action variable action iPersistent and 'Po YQQkYGGk YQQk

Transient I Accidental 'P2QkYGAGk J 'PIQk YAAk

!

I

Permanent actions (YG)

Variable actions (YG) Leading variable action

Accompanying variable action

Favourable effect YF inf 1,0 ** ** Unfavourable effect YF sup 1,35 1,5 1,5

: * See also 2.3.3.1 (3) ofEC 3: Part 1.1 (1992) I ** See Eurocode 1; in normal cases for building structures YQ,inf= °

[Source: EC 3: Part 1.1 (1992)]

Where,

Gk = is the characteristic values of the permanent actions

Qk is the characteristic values of the variable actions

11

= is the design value (specified value) of the accidental action

= is the partial safety factor for the permanent action Gk , ~

is the partial safety for accidental design situations, "fGA'~

= is the partial safety factor for the variable action Qk, ~

"fGA

"fQ

l'0,1' 1,1' 2 = Representative values of variable actions defined in Clause 2.2.2.3

ofEC 3: Part 1.1 (1992).

2.3.2 Load Factors and Combinations for the BS 5950: Part 1 (2000)

According to Clause 2.2 of BS 5950: Part 1 (2000), load factors and

combinations are taken as shown in Table 2.4.

Table 2.4: Partial factors for loads, "ff

i

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I

Loading Factor, 'Yf I Dead load 1.4

I Dead load when restraining sliding, overturning or uplift 1.0

Dead load acting together with wind load and imposed load

combined

1.2

Imposed load 1.6

Imposed load acting together with wind load 1.2

Wind load 1.4

Wind load acting together with imposed load 1.2

Forces due to temperature change 1.2

[Source: BS5950: Part 1 (2000)]

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r I I t

To obtain the design load at ultimate limit state, the load is multiplied by the

load factor obtained from Table 2.4. The dead load is multiplied by 1.4 and

imposed load multiplied by 1.6. When wind load is considered the dead load,

imposed load and wind load are multiplied by 1.2.

According to Clause 2.5 of BS 5950: Part 1 (2000), when considering the

combination of dead load, imposed load and wind load, only 80% of the imposed

load and wind will be considered.

2.4 Partial Safety Factors for materials

The values used in partial safety factors for materials in the both codes, EC 3:

Part 1.1 (1992) and BS 5950: Part 1 (2000) are different from one another. These

differences are explained in section 2.4.1 and section 2.4.2 respectively.

2.4.1 Partial Safety Factors for materials, EC 3: Part 1.1 (1992)

When considering combinations of loads consisting of more than one

variable load, EC 3: Part 1.1 (1992) adopts a method utilizing a combination

factor, 'P. According to Clause 5.1.1 of the EC 3: Part 1.1 (1992), the partial safety

factors for materials are taken as different values as shown below,

I 13

l

Resistance of class 1, 2 or 3 cross section, 'YMO = ~

Resistance of class 4 cross section 'YMI ~

Resistance of member to buckling 'YMI ~

Resistance of net section at bolt holes 'YM2 = ~

2.4.2 Partial Safety Factor for materials, BS 5950: Part 1 (2000)

According to Clause 2.1.3 of the BS 5950: Part 1 (2000), the material factor

is taken as 1.0 applied to the yield strength or 1.2 applied to the tensile strength

for structural steel.

2.5 Flexural Member Design Consideration

Generally, the EC 3: Part 1.1 (1992) and the BS 5950: Part 1 (2000) consider

almost the same design parameters in structural member design. The design

parameters considered in the EC 3: Part 1.1 (1992) are section classification, shear

resistant, moment resistant, web buckling, web crushing web crippling and

deflection. While, the design parameters considered in the BS 5950: Part 1 (2000)

include section classification, shear capacity, moment capacity, web buckling,

web bearing and deflection. Section 2.5.1 and Section 2.5.2 will show how these

factors are determined by each standard.

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2.5.1 Flexural Member Design Considerations for the EC 3: Part 1.1 (1992)

The flexural member design considerations are illustrated as follow:

(1) Classification of cross-sections

According to Clause 5.3.2, there are four classifications of cross section used

in the EC 3: Part 1.1 (1992). There are class 1, class 2, class 3 and class 4. The

classification of a cross section depends upon the proportions of its compression

element. The classes are given as in Table 2.5.

Table 2.5: Maximum width - to - thickness ratios for compression elements

Class of elementI Type of element IClass 1 Class 2 Class 3

IC/tr:S lOs Cltr:S 118 Cltf:S 15s II Outstand flange

I: for rolled section I Wed with neutral d/tw:S 728 d/tw:S 83s d/tw:S 1248 . axis at mid depth, I

I rolled sectionjIWed subject to I d/tw:S 33s d/tw:S 388 d/tw:S 42s . compressIOn, i rolled section I

I275 N/mm.4Yield strength, fy I 235 N/mm.4 355 N/mmL

1Strain, s 0.92 0.81

[Source: EC3:Part1.1 (1992)]

The factor 8 is given by 8 = (235/fy)o.s. According to Clause 5.3.5 of EC 3:

Part 1.1 (1992), for class 3, sections effective cross sectional properties can be

calculated using effective widths ofthe compression element.

15

(2) Shear resistance

According to clause 5.6.1 of EC 3: Part 1.1 (1992), calculation for resistance

to shear buckling should be made when the depth-to-thickness ratio ditw is greater

than 69E for an unstiffened web or 30s(kt)o.s for a stiffened web.

Where; d = Depth of the web

tw Web thickness

E Strain, [235/fy]o.s. (fy in N/mm2)

kt = Buckling factor for shear

According to clauses 5.4.6 ofEC 3: Part 1.1 (1992), the design value of shear

force, Vsd should not greater then VpLRd.

Where; (2.1)

Av = Shear area for rolled I and H sections

Av =A - btr + (tw+2r)tr (2.2)

For simplicity, Av can be taken as I,04htw

A = Cross section area

b = Overall breadth

h = Depth of section

tf = Flange thickness

tw = Web thickness

r = Root radius

t

I I 16

(3) Moment capacity,

The design value of the bending moment, Msd, is obtained from the clause

5.4.5 ofEC 3: Part 1.1 (1992) should not exceed the moment of resistance of the

section, Me.Rd·

Me.Rd. may be taken as follow:

a) The design plastic resistance moment of the gross section

M p1•Rd = Wplfy / yMO (2.3)

Where; Mpl.Rd design plastic moment resistance of the gross

cross-section

Wplfy = the plastic section modulus, for class 1 and class 2

section only.

yMO = partial safety factor for resistance applies to failure by

yielding.

b) The design elastic resistance moment of the gross section

Mel•Rd = Welfy / yMO (2.4)

Where; Mcl.Rd = design elastic moment resistance of the gross cross­

section

Wclfy = the elastic section modulus for class 3 sections.

17

yMO = partial safety factor for resistance applies to failure by

yielding.

c) The design local buckling resistance moment of the gross section

M o.Rd =WetTfy I yMl (2.5)

Where; MO.Rd design moment resistance of effective gross cross-

section

Wefffy = the effective section modulus, for class 4 cross

section only.

yMl = partial safety factor for resistance applies to all types

of buckling resistance of a member.

(4) Crippling resistance

For an I or H section, the design crippling resistance is;

- 0 5 2 Ef )1I2( 112Ra.Rd - • tw (yw (trltw) + 3(tw/tr)(sJd)1 yMl (2.6)

in which ss/d should not be more than 0.2. Where the member is also subject to

bending moments the following relationship should be satisfied;

Where; Ra.Rd = design crippling resistance

(2.7)

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Fsd = design shear of resistance of the cross section

Mc,Rd = design moment of resistance of the cross section

Msd design value of bending moment

tw = thickness of web

E Modulus of Elasticity

fyw is the yield strength of the web

tr= is the flange thickness

ss = is the length of stiff bearing

d Depth of the web

yMI partial safety factor for resistance applies to all types

of buckling resistance of a member.

(5) Crushing resistance.

According to Clause 5.7.3 ofEC 3: Part 1.1 (1992), for an I or H section, the

design crushing resistance is;

(2.8)

Where; (2.9)

in which br should not be more than 25tr, ss is the length of stiff bearing and O"[Ed

is the longitudinal stress in the flange. Alternatively, Sy may be obtained from;

Sy =[ 2.5(h-d) (1-( O'f.Ed/fyc)2) 112 ) I [(1+0.8 ss) I (h-d) ) (2.10)

19

Where; Ry.Rd = design crushing resistance

Ss = is the length of stiff bearing

Sy is the effective length of stiffbearing

tw thickness of web

tf= is the flange thickness

bf = width of flange

fyw = is the yield strength of the web

VMl = partial safety factor for resistance applies to all types

of buckling resistance of a member.

O"f.Ed = is the longitudinal stress in the flange

(6) Lateral torsional buckling

In Clause 5.5.2 of EC 3: Part 1.1 (1992), the design buckling resistance

moment of a laterally unrestrained beam shall be taken as;

(2.11)

Where; XLT is the reduction factor for lateral torsional buckling

~w = 1 for Class 1 or Class 2 cross-sections

~w = WeLy! WpLy for Class 3 cross-sections

~w = Weff.y! Wpl.y for Class 4 cross-sections

WpLy plastic section modulus about the y-y axis

fy = is the yield strength

20

1Ml = partial safety factor for resistance applies to all types

of buckling resistance of a member.

Msd design value of bending moment

The value of reduction factor, XLT the appropriate non-dimensional

slenderness A LT may be determined from Table 5.5.2 of EC 3: Part 1.1 (1992)

which is attached at the Table A6 of Appendix A. with A = Au and X = XLT, using

curve a (a = 0,21) for rolled sections and curve c (a = 0,49) for welded sections.

Alternatively, the value of reduction factor, XLTmay be obtained from the equation

below.

1 (2.12)XLT = r 2 - 2 fl2 ~ 1

¢LT + L¢u - ALT

- - 2 in which, ¢u=0,5 [1 +ULT (Au -0,2)+ ALl' ] (2.13)

Where; XLT= is the reduction factor for lateral torsional buckling

¢LT rotation

AlX slenderness ratio

aLT= values of imperfect factor 0,21 for rolled sections and

0,49 for welded sections

The value slenderness ratio, ALT may be determined from,

(2.14)

21

Where; ~ = JT [E/fy]O,5 = 93,38 (2.15)

8 = [235/fy] (2.16)

fy 0::: is the yield strength

Pw = 1 for Class 1 or Class 2 cross-sections

Pw WeI./ Wpl.y for Class 3 cross-sections

Pw Weff.yl Wpl.y for Class 4 cross-sections

The geometrical slenderness ratio can be obtained from the equation below.

L[!VP1{]114 IJw

ALT = 114 (2.17)

C 112[1 + L2

GI/ ] I JT2 E1w

Where; L = length of the beam between points which lave lateral

restrained.

Wpl.yo::: plastic section modulus about the y-y axis

Iz = second moment of area about minor axis

Iy second moment of area about major axis

It 0::: torsional constant

Iw 0::: warping constant

E = Modulus of Elasticity

E G shear modulus, ( )

21+v

22