A Design Tool for Circular Hollow Section (CHS) Joints

A DESIGN TOOL FOR CIRCULAR HOLLOW SECTION (CHS) JOINTS

BACHELOR OF ENGINEERING (CIVIL)

CHIONG LEE (4204123)

2011

Swinburne University of Technology (Sarawak Campus)

ABSTRACT In designing steel structures, a design engineer will first needs to select a type of sections used either open sections or hollow sections. Use of hollow sections offers wide range of benefits. Hollow sections are however not very commonly used in this world. One of the reasons is that the design of joints for hollow sections seems complicated than design of joints for conventional open sections. Design tools are widely available for open sections joints but only few simple design tools such as design graphs are available for hollow sections joints. In order to ease and facilitate the process of designing and checking of hollow sections joints, design tools must be created in the way that it saves time consumed for both design and checking. This paper included the project conducted on creating a design tool for hollow sections joints. The design tool was created using the Microsoft Office Excel spreadsheet for different geometry of hollow section joints. This design tool can be used for design in accordance with the Eurocode 3 only.

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ACKNOWLEDGEMENTS The author would like to express her sincere and special appreciation to Dr Ling Tong Wei who had guided and supervised her throughout this project. This report would not have been possible without the precious support, guidance and encouragement by him. It was such a great pleasure and honour to carry out the project under his supervision. His willingness to spare invaluable time and share his engineering knowledge will always be remembered. The author also wishes to thank her partner of the project, Evelyn Chai Pei Tze for her courage, understanding and tolerance throughout the research project. And the author would like to thank her family and friends who physically and spiritually support her whole project throughout the project.

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DECLARATION I hereby declare that: •

this thesis entitled ―A Design Tool for Circular Hollow Sections Joints‖ contains no materials which has been accepted for the award to the candidate of any other degree or diploma, except where due reference is made in the text of examinable outcome;

•

to the best of the candidate‘s knowledge contains no material previously published or written by another person except where due reference is made in the text of the examinable outcome; and

•

This report has not been previously or concurrently submitted for any other degree at Swinburne University of Technology (Sarawak Campus).

________________ Name: Chiong Lee Date: 30 May 2011

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TABLE OF CONTENTS 1.0

INTRODUCTION ...................................................................................................... 2

1.1

Background............................................................................................................. 2

1.2

Hypothesis .............................................................................................................. 5

1.3

Aim ........................................................................................................................ 5

1.4

Objectives ............................................................................................................... 5

1.5

Significance of the Research Project ....................................................................... 5

1.6

Scope of Study ........................................................................................................ 6

1.7

Source of Data and Method of Analysis .................................................................. 7

1.8

Ethical Consideration .............................................................................................. 7

2.0

LITERATURE REVIEW ........................................................................................... 1

2.1

Hollow Section Joints ............................................................................................. 1

2.2

Types of Joints ........................................................................................................ 2

2.2.1

Uniplanar Joints ............................................................................................... 2

2.2.2

Multiplanar Joints ............................................................................................ 4

2.3

Hollow Section Connections ................................................................................... 6

2.3.1

Welded Connections ........................................................................................ 6

2.3.2

Reinforced Joints ............................................................................................. 7

2.3.3

Bolted Connections .......................................................................................... 9

2.4

Design Considerations for Hollow Section Joints .................................................. 12

2.4.1

General Joints and Weld Considerations ........................................................ 12

2.4.2

Static Strength of Connections ....................................................................... 12

2.4.3

Design Procedures ......................................................................................... 14

2.4.4

Parameters Affecting Joint Resistance ............................................................ 15

2.4.5

Failure Modes for Hollow Sections Joints ...................................................... 16

2.5

The Existing Design Rules for Circular Hollow Sections Joints............................. 19 iv

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2.5.1

Eurocode 3 ..................................................................................................... 19

2.5.2

CIDECT Design Guide .................................................................................. 20

2.5.3

Others Related Design Guides........................................................................ 20

2.6

Design Tools for Circular Hollow Section Joints ................................................... 22

2.6.1

SPACE GASS................................................................................................ 22

2.6.2

Finite Element Analysis Software .................................................................. 22

2.6.3

Microsoft Excel Spreadsheet .......................................................................... 24

3.0

METHODOLOGY ................................................................................................... 25

3.1

Design Tool: Microsoft Excel Spreadsheet ............................................................ 26

3.2

Section and Joint Properties .................................................................................. 32

3.2.1

Joint Validity Checks ..................................................................................... 33

3.2.2

Design Factors and Parameters....................................................................... 33

3.2.3

Assumptions Made Throughout the Design Process ....................................... 36

3.3

Static Strength of Circular Hollow Section Joint: Eurocode 3 (BSI 2005).............. 37

3.3.1

T And Y Joints ............................................................................................... 37

3.3.2

X Joints.......................................................................................................... 39

3.3.3

K And N Joints .............................................................................................. 40

3.3.4

KT Joints ....................................................................................................... 42

3.3.5

TT Joints........................................................................................................ 44

3.3.6

XX Joints ....................................................................................................... 44

3.3.7

KK Joints ....................................................................................................... 45

3.4

User Interaction of Design Tool ............................................................................ 46

3.4.1

Design Spreadsheets ...................................................................................... 46

3.4.2

Data input on the main page ........................................................................... 46

3.4.3

Result Summary............................................................................................. 47

3.4.4

Detailed Checking Calculations ..................................................................... 47

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3.5

Verification Worked Examples and Case Studies .................................................. 48

3.5.1

SHS Joint Worked Examples by Corus Tubes ................................................ 48

3.5.2

Design Handbook for RautaRuukki Structural Hollow Sections ..................... 49

3.5.3

Worked Examples for the Design of Steel Structures (BRE, SCI, Arup) ......... 49

4.0

Results and Discussions ............................................................................................ 51

4.1

Case 1: T Joint with Axial and Moment Loading................................................... 51

4.1.1

Input Data ...................................................................................................... 51

4.1.2

Results and Discussions ................................................................................. 52

4.2

Case 2: T Joint with Axial Loading ....................................................................... 55

4.2.1

Input Data ...................................................................................................... 55

4.2.2

Results and Discussions ................................................................................. 55

4.3

Case 3: X Joint with Axial Loading ....................................................................... 58

4.3.1

Input Data ...................................................................................................... 58

4.3.2

Results and Discussions ................................................................................. 58

4.4

Case 4: Gapped K Joint with Axial Loading .......................................................... 60

4.4.1

Input Data ...................................................................................................... 60

4.4.2

Results and Discussions ................................................................................. 61

4.5

Case 5: Overlapped K Joint with Axial Loading .................................................... 65

4.5.1

Input Data ...................................................................................................... 65

4.5.2

Results and Discussions ................................................................................. 66

4.6

Case 6: Gapped N Joint with Axial Loading .......................................................... 69

4.6.1

Input Data ...................................................................................................... 69

4.6.2

Results and Discussions ................................................................................. 70

4.7

KT Joint ................................................................................................................ 74

4.8

Multiplanar Joints ................................................................................................. 74

TT Joint....................................................................................................................... 74

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XX Joint ...................................................................................................................... 74 KK Joint ...................................................................................................................... 75 5.0

CONCLUSIONS AND RECOMMENDATIONS..................................................... 77

6.0

REFERENCES ......................................................................................................... 79

7.0

APPENDICES........................................................................................................... A

Appendix A: Verification Worked Examples and Case Studies ........................................ A Appendix A1: Case 1 - T Joint with Axial and Moment Loading ............................. A1-1 Appendix A2: Case 2 - T Joint with Axial Loading ................................................. A2-1 Appendix A3: Case 3 - X Joint with Axial Loading ................................................. A3-1 Appendix A4: Case 4 - Gapped K Joint with Axial Loading .................................... A4-1 Appendix A5: Case 5 - Overlapped K Joint with Axial Loading .............................. A5-1 Appendix A6: Case 6 - Gapped N Joint with Axial Loading .................................... A6-1 Appendix B: Design Spreadsheets .....................................................................................B Appendix B1: Case 1 - T Joint with Axial and Moment Loading ............................. B1-1 Appendix B2: Case 2 - T Joint with Axial Loading .................................................. B2-1 Appendix B3: Case 3 - X Joint with Axial Loading ................................................. B3-1 Appendix B4: Case 4 - Gapped K Joint with Axial Loading .................................... B4-1 Appendix B5: Case 5 - Overlapped K Joint with Axial Loading .............................. B5-1 Appendix B6: Case 6 - Gapped N Joint with Axial Loading .................................... B6-1 Appendix B7: KT Joint............................................................................................ B7-1 Appendix B8: TT Joint ............................................................................................ B8-1 Appendix B9: XX Joint ........................................................................................... B9-1 Appendix B10: KK Joint ....................................................................................... B10-1

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LIST OF FIGURES Figure 1-1: RHS .................................................................................................................... 2 Figure 1-2: CHS .................................................................................................................... 3 Figure 1-3: CHS as best shape subjected to wind, water and wave loading (Taken from Wardenier 2001) ................................................................................................................... 3 Figure 1-4: Spanish Pavilion Shanghai Expo 2010 (Taken from Chantal 2010) ..................... 4 Figure 1-5: The highly curved structural facades support the roofs (Taken from Calzón et al. 2010) .................................................................................................................................... 4 Figure 2-1: T Joint ................................................................................................................ 3 Figure 2-2: X Joint ................................................................................................................ 3 Figure 2-3: Y Joint ................................................................................................................ 3 Figure 2-4: K Joint ................................................................................................................ 3 Figure 2-5: N Joint ................................................................................................................ 3 Figure 2-6: KT Joint .............................................................................................................. 3 Figure 2-7: TT Joint .............................................................................................................. 5 Figure 2-8: XX Joint ............................................................................................................. 5 Figure 2-9: KK Joint ............................................................................................................. 5 Figure 2-10: Butt (Groove) and Fillet Welds (Taken from Blodgett & Miller 1999) .............. 6 Figure 2-11: Weld Terminology (Taken from Blodgett & Miller 1999) ................................. 7 Figure 2-12: Full and partial penetration butt (groove) welds (Taken from Blodgett & Miller 1999) .................................................................................................................................... 7 Figure 2-13: Doubler and collar plate stiffened joints (Taken from Wardenier et al. 2008) .... 8 Figure 2-14: Grouted chords (Taken from Wardenier et al. 2008) .......................................... 8 Figure 2-15: Bolted CHS member (Taken and modified from Wardenier et al. 2008) ............ 9 Figure 2-16: Bolted end joints (Taken from Wardenier et al. 2008) ....................................... 9 Figure 2-17: Flange-plate Joints (Taken from Wardenier et al. 2008) .................................. 10

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Figure 2-18: Nailed joints (Taken from Wardenier et al. 2008) ............................................ 11 Figure 2-19: Load deformation diagram for a hollow section joint (Taken from UNI LJ n.d.) ........................................................................................................................................... 13 Figure 2-20: Main joint dimensional parameter for hollow section chords and brace members (Taken from Rey 2007) ....................................................................................................... 15 Figure 2-21: Parameters affecting joint resistance (Taken from NUS 2005)......................... 15 Figure 2-22: Sample model of SPACE GASS (Taken from TumCivil 2000) ....................... 22 Figure 2-23: Sample model of Strand7 (Taken from Strand7 2011) ..................................... 23 Figure 2-24: Sample model of SAP2000 (Taken from Graphisoft n.d.) ................................ 23 Figure 2-25: Sample model of LUSAS (Taken from LUSAS 2010)..................................... 23 Figure 3-1: Chart of Methodology ....................................................................................... 25 Figure 3-2: Data Validation ................................................................................................. 28 Figure 3-3: Drop Down List in Spreadsheet......................................................................... 29 Figure 3-4: Conditional Formatting Options ........................................................................ 30 Figure 3-5: Conditional Formating Rules Manager .............................................................. 30 Figure 3-6: Conditional Formatting feature in Microsoft Excel ............................................ 31 Figure 3-7: Code used for macro ......................................................................................... 31 Figure 3-8: T or Y Joint (Taken from BSI 2005) ................................................................. 37 Figure 3-9: Chord face failure for in-plane moment (Taken from BSI 2005)........................ 38 Figure 3-10: Chord face failure for out-of-plane moment (Taken from BSI 2005) ............... 38 Figure 3-11: X joint (Taken from BSI 2005) ....................................................................... 39 Figure 3-12: Gapped K joint (Taken from BSI 2005) .......................................................... 40 Figure 3-13: Overlapped K joint (Taken from BSI 2005) .................................................... 41 Figure 3-14: KT joint (Taken from BSI 2005) ..................................................................... 42 Figure 3-15: TT Joint (Taken from BSI 2005) ..................................................................... 44 Figure 3-16: XX Joint (Taken from BSI 2005) .................................................................... 44 Figure 3-17: KK Joint (Taken from BSI 2005) .................................................................... 45 ix

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Figure 3-18: Typical Data Input Table in Design Spreadsheets ............................................ 47 Figure 4-1: T joint under axial and moment loading - Case 1 (Taken from Oyj & Vainio 2000) .................................................................................................................................. 51 Figure 4-2: T joint under axial loading - Case 2 (Taken from Oyj & Vainio 2000) .............. 55 Figure 4-3: X joint under axial loading - Case 3 (Taken from Oyj & Vainio 2000) .............. 58 Figure 4-4: Gapped K joint under axial loading - Case 4 (Taken from Morris 2006) ............ 60 Figure 4-5: Definition of gap, g (Taken from BSI 2005) ...................................................... 62 Figure 4-6: Chord end load function for CHS joints (Taken from Corus Tubes 2005) .......... 63 Figure 4-7: Gap/lap function for CHS joints (Taken from Corus Tubes 2005) ..................... 64 Figure 4-8: Economics of Welded Joints (adapted from Whitfield & Morris 2009) ............. 64 Figure 4-9: Overlapped K joint under axial loading - Case 5 (Taken from Morris 2006) ...... 65 Figure 4-10: Definition of overlap ratio (Taken from BSI 2005) .......................................... 67 Figure 4-11: N joint under axial loading - Case 6 (Taken from BRE, SCI, Ove Arup & Partners 1994) ..................................................................................................................... 69 Figure 4-12: Outline of 30m span truss (Taken from BRE, SCI, Ove Arup & Partners 1994) ........................................................................................................................................... 71 Figure 4-13: Influence of gap and overlap on eccentricity (modified from Whitfield & Morris 2009) .................................................................................................................................. 72

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LIST OF TABLES Table 2-1: Failure modes for CHS joints (Recompiled from Oyj & Vainio 2000) ................ 17 Table 3-1: Excel Functions Used in Spreadsheet ................................................................. 26 Table 3-2: Sections and joint properties (BSI 2005)............................................................. 32 Table 3-3: Range of validity for welded joints between CHS chords and braces members (T7.1 Eurocode 3-2005) ...................................................................................................... 33 Table 3-4: Design Factors and Parameters (BSI 2005) ......................................................... 34 Table 3-5: Type of joints and verification sources ............................................................... 50 Table 4-1: Data input for Case 1 .......................................................................................... 51 Table 4-2: Validity Check for Case 1 .................................................................................. 52 Table 4-3: Axial and Moment Resistance Check for Case 1................................................. 52 Table 4-4: Data input for Case 2 .......................................................................................... 55 Table 4-5: Axial Resistance Check for Case 2 ..................................................................... 55 Table 4-6: Data input for Case 3 .......................................................................................... 58 Table 4-7: Axial Resistance Check for Case 3 ..................................................................... 59 Table 4-8: Data input for Case 4 .......................................................................................... 60 Table 4-9: Validity Check for Case 4 .................................................................................. 61 Table 4-10: Axial Resistance Check for Case 4 ................................................................... 61 Table 4-11: Data input for Case 5 ........................................................................................ 65 Table 4-12: Validity Check for Case 5 ................................................................................ 66 Table 4-13: Axial Resistance Check for Case 5 ................................................................... 66 Table 4-14: Data input for Case 6 ........................................................................................ 69 Table 4-15: Validity Check for Case 6 ................................................................................ 70 Table 4-16: Axial Resistance Check for Case 6 ................................................................... 70

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LIST OF SYMBOLS AND ABBREVIATIONS Abbreviations of Organizations AISC

American Institute of Steel Construction

API

American Petroleum Institute

AWS

American Welding Society

BRE

Building Research Establishment

CIDECT

Comité International pour le Développement et l‘Étude de la Construction Tubulaire (International Committee for the Development and Study of Tubular Structures)

IIW

International Institute of Welding

SCI

Steel Construction Institute

Other abbreviations CHS

circular hollow section

FEA

finite element analysis

RHS

rectangular or square hollow section

General Symbols A

cross-sectional area

Ag

gross cross-sectional area of CHS

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Ai

cross-sectional area of member i

An

net cross-sectional area of CHS

Av

shear area of the chord

di

overall diameter of CHS member i (i = 0, 1, 2 or 3)

e

noding eccentricity for a joint – positive being towards the outside of the truss

E

modulus of elasticity

fyi

yield strength of member i (i = 0, 1, 2 or 3);

fy0

yield strength of a chord member;

g

gap between the brace members in a K or N joint (negative values of g represent an overlap q )

k

factor defined in the relevant table, with subscript g, m, n or p

lc

length of a collar plate

ld

length of a doubler plate

M*

moment or flexural resistance of a joint, expressed as a moment in the brace

Mip,i,Rd

design value of the resistance of the joint, expressed in terms of the in-plane internal moment in member i (i = 0, 1, 2 or 3);

Mip*

design value of the in-plane internal moment in member i (i = 0, 1, 2 or 3);

Mop,i,Rd

design value of the resistance of the joint, expressed in terms of the out-ofplane internal moment in member i (i = 0, 1, 2 or 3);

Mop*

design value of the out-of-plane internal moment in member i (i = 0, 1, 2 or 3);

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Mpl,i

plastic moment capacity of member i

np

ratio (σp,Ed / fy0 ) / γM5 (used for CHS chords)

N*

axial force applied to member i (i = 0, 1, 2)

Ni,Rd

design value of the resistance of the joint, expressed in terms of the internal axial force in member i (i = 0, 1, 2 or 3)

Npl,Rd

design plastic resistance to normal forces of the gross cross-section

p

length of the projected contact area of the overlapping brace member onto the face of the chord, in the absence of the overlapped brace member

q

length of overlap, measured at the face of the chord, between the brace members in a K or N joint, see Figure 1.3(b);

V

shear force

Vpl,0

shear yield capacity of the chord

Vpl,Rd

plastic design shear resistance

β

ratio of the mean diameter or width of the brace members, to that of the chord

γ

ratio of the chord width or diameter to twice its wall thickness:

γM

partial safety factor for joint resistance

λov

overlap ratio

μ

correction factor accounting for multiplanar effect to be applied to uniplanar joint strength

Ф

joint resistance (or capacity) factor (approximate inverse of γM )

ϕ

angle between the planes in a multiplanar joint.

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σ0,Ed

maximum compressive stress in the chord at a joint;

σp,Ed

value of σ0,Ed excluding the stress due to the components parallel to the chord axis of the axial forces in the braces at that joint

θi

included angle between brace member i and the chord (i = 1, 2 or 3);

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INTRODUCTION

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HES 5108 RESEARCH PROJECT

INTRODUCTION

1.1 Background The use of hollow structural sections (HSS) has extensively expanded over the years. HSS are now broadly used as structural members in buildings, offshore structures, bridges, railway stations, ports and other structures. There are 2 types of HSS that are commonly used in structural construction. They are Circular Hollow Sections (CHS) and Rectangular Hollow Sections (RHS) as shown in Figure 1-1 and Figure 1-2. There are many examples in nature that had proven the outstanding static properties of the CHS as structural members (Wardenier 2001). HSS is made from steel which can be fully recycled. This makes HSS sustainable material to be used in structures. It has high quality surface finish and aesthetically pleasing. Thus, CHS is always chosen to be used to design an architecturally attractive shape in a structure. CHS are excellent in resisting compression, tension, bending and torsion. Due to their properties of less resistance to air and water flow, CHS are proven to be the best shape especially for structural members subjected to wind, water or wave loading as shown in Figure 1-3 (Tata Steel 2010). They are less weight and yet stronger than other material such as concrete. They are also cost effective if compared to other building materials.

Figure 1-1: RHS

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Figure 1-2: CHS

Figure 1-3: CHS as best shape subjected to wind, water and wave loading (Taken from Wardenier 2001)

Application of Hollow Sections The application of hollow sections covers various fields due to its high aesthetic value and high geometrical properties. Nowadays, architectural appearance becomes more important. As hollow sections themselves has high aesthetic value, they are widely used in the construction of building, halls, bridges, barriers, offshore structures as well as towers (Wardenier 2001). The hollow section joint designs are commonly applied in columns, uniplanar trusses, multiplanar trusses, spaces structures and even composite structures (Wardenier 2001). Hollow sections are mainly used for columns in buildings. As hollow sections are very efficient in compression, they are suitable to design trusses either in uniplanar or multiplanar. The members are usually welded directly to each other in hollow sections trusses. Besides, HSS is widely utilized in space structures nowadays.

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A very recent example of superstructure that used CHS as its structural and architectural elements is the Spanish Pavilion in Shanghai Expo 2010 as shown in Figure 1-4. It used CHS in the highly curved structural façade supporting the roofs of exhibition rooms without any inner columns as shown in Figure 1-5 (Calzón et al. 2010). The hypothesis, aim, objectives and significance of this research project will be discussed next.

Figure 1-4: Spanish Pavilion Shanghai Expo 2010 (Taken from Chantal 2010)

Figure 1-5: The highly curved structural facades support the roofs (Taken from Calzón et al. 2010)

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1.2 Hypothesis Microsoft Excel Spreadsheet can be used to create a design tool in determining the static design capacities of uniplanar and multiplanar joints in either hot finished or cold formed circular hollow sections.

1.3 Aim The main aim of this research project is to generate a design tool in order to determine the static design capacities of uniplanar and multiplanar joints in steel CHS. Besides, the design tool created should be able to design joints in either cold formed or hot finished CHS.

1.4 Objectives 1. To identify the kinds of design tools that can be used in designing and checking CHS joints design. 2. To ensure that the design tool generated be able to design either cold formed or hot finished CHS joints. 3. To apply the design rules and main features in Eurocode 3 related to CHS joints in the design tool created. 4. To identify design checking procedures for static design capacities of uniplanar and multiplanar joints in CHS in accordance with Eurocode 3- 2005. 5. To verify the design spreadsheets by comparing the result outcomes with case studies. 6. To review on the design assumptions and recommendations made by previous researchers when designing the hollow section joints.

1.5 Significance of the Research Project In the engineering design, a member design capacity is higher as compared to the design capacity of a joint. Hence, a design is always limited by the joint capacity. Therefore,

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alternative needs to be developed. Members can be chosen according to its capacity as well as the joint‘s capacity. Finite element software can be an alternative for the CHS joint designs. However, pre-study and training are needed in order for a user to use it. The user needs to understand the theory behind clearly and he should have own judgement in using the outcomes as the software will gives outcome with any input. As Microsoft Excel is commonly used among engineers and designers, it appears as a handy alternative to design hollow section joint. It saves time in all the design stages including the preliminary and final design. It can also be used to create the calculation report that suitable for immediate submission. The design tool created for hollow section joint design will beneficial design engineers. This will help to reduce the joint design time and ease the design checking, such as the adequacy of joint capacities (resistances). Any decision made in design stage influences joint capacity, fabrication and erection of a structure. By using design tool created, capacities of joints are checked to be adequate. Consequently, design engineer can avoid time consumed for repetitive works.

1.6 Scope of Study This project is mainly focus on developing a design tool for both uniplanar and multiplanar joints in CHS. The design in uniplanar joints includes K joint, KT joint, N joint, T joint, X joint, and Y joint whereas the design in multiplanar joints includes KK joint, TT joint and XX joint. Alternative design tool such as software used for CHS joints will be reviewed. Analysis and design will be conducted using Microsoft Excel Spreadsheets. Also, the analysis and design will be conducted solely in accordance with Eurocode 3 - 2005: Design of steel structures. However, other design guides will be reviewed. Failure modes of joints will be evaluated. Only static analysis will be considered in this project.

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1.7 Source of Data and Method of Analysis Research Strategy is essential in directing and conducting the process of research systematically. The topic of study is first identified and developed. The topic chosen is ―A Design Tool for Circular Hollow Section Joints‖. Background information of hollow section joint is collected and then related sources are gathered. Literature of the hollow section joints and its alternative design tool are reviewed. Microsoft Excel Spreadsheets are the main computer application used to create design tool in order to achieve the aims of the study. Primary data will be obtained from the spreadsheets for further interpretation and discussion. There will be also researches done based on the work of other authors that source from the library and online databases. The information obtained from journal papers, articles and books are all secondary data. Next, the findings are evaluated. Besides, appropriate citation is used to cite the findings of previous researchers.

1.8 Ethical Consideration Engineering ethics are always linked to the design practices throughout design processes. The main ethical issues involved in the context of engineering design are safety and sustainability. Both safety and sustainability issues play important role in engineering applications, planning and design. Safety is very crucial in any of the engineering designs. It is important that a structure designed is safe by adopting safety factors and also complying with the design rules. Adequacy checks need to be done in any cases to ensure the adequacy of the design. Material choosing is a concern in sustainable design. Steel is characteristically recyclable and reusable. Its durability and quality make it a sustainable material and highly favoured. A sustainable design is the design that could cater the needs of present as well as future generation. So, it is essential to adopt suitability concept in any design. Most of the CHS joints are welded joints. Welded joints will last longer if compared to bolted joints. Other than that, welded joints will need less maintenance or repairs if they are well coated and galvanised. Therefore, this will reduce the construction cost and also future maintenance cost.

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LITERATURE REVIEW

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HES 5108 RESEARCH PROJECT

LITERATURE REVIEW

2.1 Hollow Section Joints According to Eurocode 3 - 2005, ―Joint‖ refers to the region where two or more members are interconnected. The main or through member of a joint is ―chord‖ and ―brace‖ is the member attached to a chord (BSI 2005). Unlike joints used in open sections such as I or H sections, joints in hollow sections are less convenient for fitting plates and bolts. Therefore, welds are widely used for connecting hollow sections. In other words, Circular Hollow Sections (CHS) joints are constructed by welding the brace, onto the chord. Welded joints hold the brace and chord member together as an integral part of the structure. Therefore, the effectiveness of the joints greatly governs the success and stability of a structure (Whitfield & Morris 2009). In the initial stage of design, the designer need to determine the welded joint capacity based on the affecting parameters. Factors that affect the capacity of the HSS are member sizes, steel grades as well as joint geometry. Other than joint capacity, the fabrication and erection of the structure are main concerns in designing a hollow sections joint. Sometimes, it can be too late to change section size, grades or even the geometry for under-designed joint (Whitfield & Morris 2009). As the member capacity at most of the time is larger than joint resistance (capacity), it is important to take care of the joint capacity to avoid the case of under-designed joint which results in inadequate design. Therefore, adequate design considerations in any part of design processes will ensure a technically safe, economically feasible and architecturally attractive structure.

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2.2 Types of Joints CHS joints are generally categorized based on their geometry configuration and loading condition (NUS 2005). There are two main types of configurations in CHS joints. They are uniplanar and multiplanar joints.

2.2.1 Uniplanar Joints In uniplanar joints, the brace members are connected to the chord members on a single plane. The chord and brace members lie in one plane for all the uniplanar joints. The common types of uniplanar CHS joints include X joint, T joint, Y joint, N joint, K joint and KT joint. The brace sections are welded to the surface of chord section. Figure 2-1 to Figure 2-6 show the types of configuration of uniplanar joints in HSS. The classification of hollow sections joints is based on the load transfer instead of the appearance of the joint. T joint is a special case of Y joint. A joint is classified as X joint when the normal force is transferred through chord members and equilibrated by a brace member (Wardenier et al. 2008). When the normal brace member is equilibrated by the chord member perpendicularly, the joint is classified as T joint. The joint is categorized as Y joint when the brace member is not connected to the chord member perpendicularly. A K joint is the joint when normal brace members force is equilibrated by the other two brace members on the same side. An N joint is considered as unusual type of K joint (Wardenier et al. 2008). KT joint is combination of a K and a T joint on the same side of chord.

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Figure 2-1: T Joint

Figure 2-2: X Joint

Figure 2-3: Y Joint

Figure 2-4: K Joint

Figure 2-5: N Joint

Figure 2-6: KT Joint

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By referring to EC3, the formula involved in designing both T and Y joints are same. So, the design spreadsheet created can be combined and made in a flexible way. The design spreadsheet will then usable for both T and Y joints. This applies to K and N joints as well. The method of creating the design spreadsheets will be further explained in Section 0. K, N and KT joints can be either gapped or overlapped. Overlap and gap joints behave in different ways. Their capacities are affected by parameters respectively. The affecting parameters will be further discussed in the Section 2.4.4.

2.2.2 Multiplanar Joints In multiplanar joints, brace sections are connected to the chord sections in multiple planes. Three large groups of multiplanar joints are XX joint, TT joint and KK joint. The Figure 2-7, Figure 2-8, and Figure 2-9 show the configuration of the multiplanar joints. The ultimate behaviours of multiplanar joints are similar to those of the uniplanar joints. A reduction factor will be multiplied to the uniplanar joint capacity in order to obtain multiplanar joint capacity (BSI 2005). The reduction factor used for TT joints is 1.0 (BSI 2005). Mitri et al. (1987) carried out tests on TT joint with a 90o between both braces that are loaded in compression. The finding shows that the joint resistance (capacity) did not vary significantly. The multiplanar effects are most significant for XX joints as shown in Figure 2-8. CIDECT (2008) stated that the FEA had proven that the multiplanar loading has a significant effect on the strength or the resistance (capacity) as compared to a uniplanar X joint. In the case of load acting in one plane with same magnitude as those in other plane in opposite loading sense (compression and tension), the joint resistance could drop around 1/3 of a uniplanar X joint. In contrast, when the loading are in the same sense, the joint strength will increase. This phenomenon was captured and will be further discussed in Section 4.0. These will be applied into the design spreadsheets when creating design spreadsheets for multiplanar joints. CIDECT (2008) suggested reduction factor of 1.0 for KK joints instead of 0.9 in EC3 (2005). To be conservative, the reduction factor of 0.9 is adopted for the design speadsheet for KK joint since the design tool is created solely in accordance with EC3 (2005).

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Figure 2-7: TT Joint

Figure 2-8: XX Joint

Figure 2-9: KK Joint

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2.3 Hollow Section Connections 2.3.1 Welded Connections Welding is the only joining method that creates a truly one-piece member.

All the

components can efficiently and effectively transfer loads from one piece to another in welded joint (Blodgett & Miller 1999).

2.3.1.1 Welding Types Corus (2005) suggested that the weld for tubular joints should generally be made around the whole border or circumference of the brace section using butt (groove) weld, fillet weld or combination of the two. The Figure 2-10 shows the illustration of butt and fillet welds.

Figure 2-10: Butt (Groove) and Fillet Welds (Taken from Blodgett & Miller 1999)

Fillet welds have a triangular cross section. They are normally applied directly onto the surface of materials they join as show in Figure 2-10. The leg size as shown in Figure 2-11 indicates the size of a fillet weld. Another common weld used for tubular joints is butt weld or also called as groove weld. Figure 2-12 shows the two types of butt weld, full penetration and partial penetration butt welds. Full penetration butt welds have a throat dimension which is equal to the thickness of the surface or section they are joined with (Blodgett & Miller 1999). On the other hand, partial penetration butt weld has a throat dimension which is less than the thickness of the material they join. Welded connections are used in CHS joints as welding offers many benefits over bolting. Welded joints directly transfer stress between members. Without gusset plate or splice in bolted joints, the weight of the joint is minimal. Fillet weld are more commonly used as it is convenient and requires less erection as well as preparation of edge.

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The design tool created assumed that all the CHS joints are welded joints with sufficient design resistance (capacity) of welds.

Figure 2-11: Weld Terminology (Taken from Blodgett & Miller 1999)

Figure 2-12: Full and partial penetration butt (groove) welds (Taken from Blodgett & Miller 1999)

2.3.2 Reinforced Joints In order to improve the joint capacity, different reinforcing methods have been introduced in engineering practices (Shao et al. 2010). The reinforced joints have higher ultimate capacity toward resistant and higher stiffness.

Besides, reinforcement is also applied for the

enhancement of under-dimensioned joints (Shao et al. 2010).

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Two types of reinforcing methods are inner reinforcement and outer reinforcement. Stiffeners are placed inside the chord for inner reinforcement.

The examples are ring

stiffeners (Lee & Llewelyn-Parry, 2004; Lee & Llewelyn-Parry, 2005) and inner plate reinforcement (Shao et al., 2009). On the opposite side, stiffeners are placed outside the chord for outer reinforcement. The examples are doubler-plate (Hoon et al., 2001; Fung et al., 1999) and collar plate reinforcement (Choo et al., 2005). Figure 2-13 shows the illustration of doubler and collar plate stiffened joints. In addition, grouting (Wardenier et al. 2008) can be another of reinforcement in tubular joints as shown in Figure 2-14. Grouting of joints is used to improve the static capacity of CHS joints and increase the joint rigidity. However, the grouted could add weight in the joint. More future research need to be carried out to determine whether the added static capacity would overweigh the weight added onto the joint or not. The design spreadsheets created will not cater for a grouted joint.

Figure 2-13: Doubler and collar plate stiffened joints (Taken from Wardenier et al. 2008)

` Figure 2-14: Grouted chords (Taken from Wardenier et al. 2008)

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2.3.3 Bolted Connections 2.3.3.1 Bolted Types According to CIDECT Design Guide (2008), plates, forks, T sections or cut-outs of I sections are welded to the CHS member as shown in Figure 2-15 and Figure 2-16. Besides, slotted gusset plate and flattened bolted end joints are also commonly used for bolted hollow section joints.

Figure 2-15: Bolted CHS member (Taken and modified from Wardenier et al. 2008)

Figure 2-16: Bolted end joints (Taken from Wardenier et al. 2008)

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Flange-plate Joints A flange-plate joint as shown in Figure 2-17 is one type of the joints with bolts in tension. Many researches were conducted based on this kind of bolted joint. Conventionally, limit states for this joint are yield of end plate, welded strength, as well as tensile strength of bolts. Prying action is involved in this joint as well.

Figure 2-17: Flange-plate Joints (Taken from Wardenier et al. 2008)

Nailed Joints Another bolted joint that can be used in CHS is nailed joint where CHS will be nailed together. The nails are arranged in such a way that they are symmetrically around the circumference of the section as shown in Figure 2-18. Alternatively, tubular collar can be used to connect both sections with same outer diameter (Wardenier et al. 2008).

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Figure 2-18: Nailed joints (Taken from Wardenier et al. 2008)

Recommendations for bolted CHS joints are not provided in the codes. However, the design and checking might still have to comply in the normal method according to the possible failure modes. Shear, stress and failure net cross sectional area are the important parameters in the bolted connection design as they affect the bolted joint capacity. However, since welded connection are more commonly used in CHS joints, bolted connection is not considered in the design tool created for CHS joints.

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2.4 Design Considerations for Hollow Section Joints 2.4.1 General Joints and Weld Considerations There were some reviews done on the general joint considerations stated in CIDECT Design Guide 1. Some of the critical considerations will affect the joint efficiency. Wardenier et al. (2008) suggested that the chords should normally have a thicker wall. This is important as a thicker wall has higher stiffness which helps in resisting loads from brace sections. This is relevant because the formulae for the joint axial resistance are always multiply by the square for chord thickness. This will results in higher joint resistance as the diameter to thickness ratios decrease. On the other hand, a large thin section is more suitable for a compression chord to resist buckling. However, this will always compromise with the joint strength and as a result stocky sections will need to be chosen. A thin wall is appropriate for a brace member except for overlap joints. According to Wardenier et al. (2008), as the ratio of brace wall thickness to chord wall thickness increases, the joint resistance increases. It is valid because the ratio of chord wall thickness to brace wall thickness is correlation to the joint resistance (capacity). In order to provide ease way in welding, it is suggested that CHS brace have smaller width as compared to the chord members, especially for joint at the saddle of chord member (Wardenier et al. 2008). Besides, gapped joints are more preferred for K and N joints as this ease the process of preparation, fit and weld (Wardenier et al. 2008). The suggestions on joints considerations will be further verified using the design tool created. The outcomes will be discussed in the Section 4.0.

2.4.2 Static Strength of Connections Investigation on the loading strengths of welded hollow section joints of different types were done by previous researchers. The loading types can be axial tension, compression, in-plane and out-of-plane bending or their combinations.

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Figure 2-19: Load deformation diagram for a hollow section joint (Taken from UNI LJ n.d.)

The Figure 2-19 shows the load deformation diagram of a hollow section joint loading in tension and compression. The static strength of hollow section joint can be characterized by few criteria according to its deformation. The criteria are ultimate load-bearing resistance, deformation limit and crack initiation. The ultimate load capacity is thus the prior criteria to be met in determining the static strength of a joint. Previous research had found out that the present ultimate strength equation based on each connection tests exactly forecast the capacity of connection when trusses are loaded under static loads (Kurobane 2002). The connections reach their ultimate loads in either wall plastification failure or brace local buckling (Kurobane 2002). There are 2 failure modes that are critical in the CHS joints. There are chord face failure and punching shear failure. Eventually, joint strength is governed by chord face failure (plastification) as it has lesser resistance as compared to punching shear in CHS joints. This will be proven in the Section 4.0.

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2.4.3 Design Procedures The static design procedures can be simplified into 3 general steps. First, the design member forces in brace and chord need to be determined. Then, the next step is to determine the design resistance of the joint (Zhao et al. 2010). Design rules from structural codes can be adopted for the design for joints. Then the final step is to apply the design criteria to assess whether the joint is sufficient or not. By comparing the design action and design resistance, the joint is assessed (Zhao et al. 2010). Their failure modes are considered in this stage. Failure modes are to be discussed in section 2.4.5. Minimum value fulfilling these criteria will be the design resistance of the joint.

For

multiplanar joints, it is essential to consider the correction factors together with the design criteria in relevant plane of uniplanar joints (Zhao et al. 2010). These general procedures will be adopted in the process of creating and verifying (the design spreadsheet for each uniplanar and multiplanar joint in Section 0 and 4.0 respectively. The design member forces in brace and chord are obtained from the case studies. This design tool is created in accordance with the Eurocode 3 – 2005. The geometry validity of the joint is first checked. The strength of the joint is then determined by getting the least resistance (capacity) of failure modes involved. A joint is considered sufficient or adequate when the design action is lesser than that of design resistance. This means the joint is able to resist and cater the design loading acting on it.

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2.4.4 Parameters Affecting Joint Resistance

Figure 2-20: Main joint dimensional parameter for hollow section chords and brace members (Taken from Rey 2007)

Figure 2-21: Parameters affecting joint resistance (Taken from NUS 2005)

The non-dimensional parameters affecting the joint capacity and resistance are illustrated in Figure 2-21. The ratio of the mean diameter or width of the brace members to the chord (refer Figure 2-20), β, can be used to determine the possible load paths under varies loading circumstances (NUS 2005). When β increase, the joint resistance will increase also as discussed in Section 2.4.1.

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The ratio of the chord diameter to twice its wall thickness, γ, donates the resistance of chord wall due to bending, shearing and membrane action. The joint resistance will increase when this parameter is reduced. Both of these parameters are involved in calculating the joint resistance (capacity) in the design spreadsheets. Besides these 2 parameters, the bracing angle, θ will also influence the joint capacity in the way that when θ getting smaller, the capacity of the joint increases significantly. This will be further discussed in Section 4.0. The gap, g is the gap between brace members in a K or N joint as shown in Figure 2-20 and Figure 2-21. Gap will substantially influence a factor in joint resistance, kg. Large gap results in eccentricity and secondary bending. However, these effects will be eliminated in joint design if the intersection of the centre lines of the brace members are within the validity range. Usually, gap connections are more preferable as compared to overlap connections. The reason is that it is easier to prepare, fit and weld brace members onto a chord member. Minimal gap of summation of thickness chord and brace members need to be provided. More information on gap, overlap and eccentricities will be discussed in the Section 4.0 (Case 4, 5 and 6).

2.4.5 Failure Modes for Hollow Sections Joints As mentioned in the EC3 (2005), there are generally six failure modes that affect the design of joint resistance between CHS and of connection between CHS. The failure modes due to axial loading and bending moment are shown in the Table 2-1 with its illustration as applicable. When the joint satisfied the validity checks, the critical failure modes are recognized for each load and type of joint. The non-critical modes are not necessary in order to reduce volume of work in calculations. On the other hand, the non-critical failure modes might become critical when the joint parameters do not satisfy the validity checks.

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Table 2-1: Failure modes for CHS joints (Recompiled from Oyj & Vainio 2000)

Failure modes

Descriptions

Plastic failure of the chord a) Chord face failure

Brace

face (plastification).

Chord

Yielding, crushing or

Brace

instability (crippling or b) Chord side wall failure

buckling of the chord side wall or chord web) due to compression. Chord

Brace c) Chord shear failure

Shearing between chord and brace member.

Chord

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Brace d) Chord punching shear failure

Crack initiation and leads to rupture of brace members through the chord member. Chord Cracking in the welds or in

Brace

the brace members. e) Brace failure with reduced effective width

Due to insufficient brace cross sectional area that leads to overload. Chord Brace

Chord Failure of either brace or f) Chord or brace Local

chord member at the joint

buckling failure

location. Due to non-uniform

Chord local buckling Brace

stress distribution.

Chord Brace local buckling

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2.5 The Existing Design Rules for Circular Hollow Sections Joints There are various standards and design guides that are available worldwide for the design of steel structures. However, there are only parts of the standards and design guides contain the design of hollow section joint under static loading.

2.5.1 Eurocode 3 The European Standard or simply called as Eurocode has now gradually superseding other design codes in the design and construction sectors of Civil and Structures in many parts of this world. European Standard, Eurocode 3 is the eurocode used for the design of steel structures. It covers the design of buildings and most of the civil engineering works in steel.

Hollow Sections Joints The Chapter 7 of the EC3, hollow section joints was reviewed. This chapter provide design rule used for both uniplanar and multiplanar CHS joints. Failure modes for CHS joints are reviewed and discussion Section 2.4.5.

Range Of Validity Range of validity for welded joints between CHS brace members and CHS chords was reviewed. For joints within the range of validity provided in Table 7.1 in EC3, only chord face failure and punching shear need to be taken into consideration. Range of validity will be further elaborated and discussion in Section 3.2.1 as well as Section 4.0.

Design Resistances Design rules for uniplanar joints are stated in the EC3. Formulae are provided for design axial resistances of welded joints between CHS. Other than that, the EC3 also gives details on the design resistance moment of welded joints between CHS brace members and CHS chords.

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There are also design rules provided on the multiplanar CHS joints. Reduction factors for multiplanar joints such as TT, XX, and KK joints are listed together with its criteria respectively. The reduction factors used were briefly discussed in Section 2.2.2. The minimum value for chord face failure and punching shear should be taken as design resistance. The design resistance will then be used to compare with the design action forces or moments in a joint. The joint is considered adequate when the design action is less than that of its resistance (capacity).

2.5.2 CIDECT Design Guide Other than the EC3, the design guides published by CIDECT was reviewed. CIDECT, Comité International pour le Développement et l‘Étude de la Construction Tubulaire stand for International Committee for the Development and Study of Tubular Structures. It is an international association of hollow section manufacturers based in Geneva. The committees do research on the application of hollow section worldwide. Committees of CIDECT had summarized the current state-of-the-art of this field in their publication. CIDECT Design Guides 1 and 3 are based on the IIW sub commission XV-E design recommendation which focus of the static strength of tubular joints (Packer 2000). CIDECT Design Guide 1 covers the designs for circular hollow section (CHS) joints under predominantly static loading. This design guide includes the statically loaded, welded and bolted CHS connection in accordance with the IIW recommendations. Some of the recommendations were discussed in Section 2.4 and some will be included in Section 4.0 as well.

2.5.3 Others Related Design Guides The CISC had also published design guides for onshore tubular structures by expanding the present information available from CIDECT and IIW and integrating it to the Canadian standards (Packer 2000). In USA, the designs of hollow sections joints are conformed to the American Welding Society (AWS). The connection static design rules of CHS are based on American Petroleum Institute (API) rules for offshore structures.

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American Institute of Steel Construction (AISC) published a specification for the design of HSS (Packer 2000). Although the Australia Standards (AS) covers most of the design rules for steel structures, it is limited to the hollow sections joints design. However, AS4100 does cover the member design of hollow section. British Standards Institution (BS 6235) Code of practice for fixed offshore structures covers the design of hollow section joints for offshore structures (Dale

2005).

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2.6 Design Tools for Circular Hollow Section Joints 2.6.1 SPACE GASS SPACE GASS is a commonly used for structural analysis and design program especially in 2D and 3D frames, trusses, grillages and beams (SPACEGASS 2011). It has the features of design ranging from small beams, trusses to large high rise buildings as shown in Figure 2-22. However, the hollow section joint design is not included in this program.

Figure 2-22: Sample model of SPACE GASS (Taken from TumCivil 2000)

2.6.2 Finite Element Analysis Software The use of finite element analysis (FEA) packages is one of the important factors that boost the development of hollow sections joints studies since the late 1980s (Kurobane 2002). FE has the advantage of stimulating actual behaviour of connections up to failure based provided there is a numerical model which is well calibrated against experimental results (Rahman 2005). The FE analysis has the advantage that it can model complicated geometry especially in multiplanar joint designs. It can also analyse non-linear behaviour related to high deformation and nonlinear material (Rahman 2005). Everything has its pros and cons, so as the FE analysis. A professional is needed in order to model the exact situation into the FE software (Rahman 2005). FE analysis gives output for any input of or model. So the designer should have own judgment to interpret the result obtained from FE analysis. The Figure 2-23, Figure 2-24, Figure 2-25 shows examples of FE analysis software. There are STRAND7, SAP2000, and LUSAS.

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Figure 2-23: Sample model of Strand7 (Taken from Strand7 2011)

Figure 2-24: Sample model of SAP2000 (Taken from Graphisoft n.d.)

Figure 2-25: Sample model of LUSAS (Taken from LUSAS 2010)

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2.6.3 Microsoft Excel Spreadsheet Microsoft excel is one of the tools can be used for structural design. There are many examples that excel can be a very useful and unique tool to be used in structural design. The functions of storing, manipulating and graphing data make it a very useful spreadsheet application (Lemoine 2011). Microsoft Excel allows custom macros and Visual Basic add-ons for users with specific needs and programming experiences (Lemoine 2011). Instead of getting some complicated and costly software, Microsoft excel can be chosen as a design tool in structural design. It is cost effective as almost every engineering firm has Microsoft Excel. Most of the engineers are familiar with the standard interface in Excel. Excel is easy to be used and there are helpful wizards to guide new users through complex processes. Lemoine (2011) found that Microsoft excel has extraordinary large amount of data storage. Users can store up to 1 million rows by 16,000 columns. He also added that PivotTables is one of the great features in Excel where it assists user in getting the outcome in a fast, easy and accurate way. The conditional formatting features enable user to create the calculation in the form of report so that it can be directly printed as calculation reports when the checking is done. This save time as paperwork is always time consuming. Also, the user do no need to worried that the receiver cannot open or access the file as Microsoft Excel is very commonly used in this world. Even different versions of excel files are compatible with each other. Nowadays, Excel spreadsheets can be inserted or imported within various popular applications. This makes Excel even more useful and flexible. Hence, Microsoft Excel is chosen as the design tool for hollow sections joints in this project. The method of analysis using Microsoft excel spreadsheets is further discussed in Section 0.

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3.0 METHODOLOGY The methodology used to achieve the objectives of the research study on the design tool of hollow sections joints is discussed in this chapter. The design tool was designed in accordance with the Eurocode 3 (BS EN 1993 1-8: 2005). Study was done on the Eurocode 3 for the design rules and the principle used for CHS joints design. Different types of Circular Hollow Sections (CHS) joints are then analyse and applied in the design tool. The Microsoft Excel spreadsheet is chosen as the main design tool of the CHS joints. The findings are then further verified with chosen worked examples and case studies in Section 4.0. Next, discussions are done by comparing the outcomes of comparison between design spreadsheets and case studies in Section 4.0 also. The following Figure 3-1 shows the flow of the methodology of the project.

Research on the structural design standards for circular hollow section joints.

Familiar with the design rules and principle in the Eurocode.

Conduct design analysis for circular hollow section joints of different types.

Create design spreadsheets in Microsoft Excel for design of circular hollow section joints.

Compare the findings from design spreadaheets with case studies chosen.

Discuss the outcomes of comparison between design spreadsheets and case studies.

Conclude the outcome and recommend future works based on the result outcomes.

Figure 3-1: Chart of Methodology

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3.1 Design Tool: Microsoft Excel Spreadsheet As mentioned earlier, the main design tool used for the design of CHS joints was Microsoft Excel Spreadsheet. The design was done solely based on the EC3. Different types of functions and features of Microsoft Excel were used in the creation of the spreadsheet for CHS joints design. The Table 3-1 shows the function used throughout the design analysis in the spreadsheet with its descriptions and examples. Table 3-1: Excel Functions Used in Spreadsheet

Excel Functions

Description

Abs

Gives the absolute value of a number E.g. Abs (-150) will give the outcome of 150. This is usually used to obtain magnitude of force as it can be negative (tension).

And

Returns TRUE if all conditions are TRUE. It returns FALSE if any of the conditions are FALSE. E.g. And ( Cell A=‖OK‖, Cell B=‖OK‖) will give the outcome of TRUE if both cells display OK or FALSE otherwise.

FALSE

Returns a logical value FALSE.

If

Returns one value if a specified condition evaluates to TRUE, or another value if it evaluates to FALSE. E.g. If (RATIO>1, ―NOT OK‖, ―OK‖) will give the outcome of NOT OK is the cell RATIO is greater than 1 or OK otherwise.

Match

Searches for a value in an array and returns the relative position of that item. E.g. Match (―Area‖, B1:P1, 0) will give the relative positive of ―Area‖ in the array B1:P1 exactly.

Max

Gives the maximum value in a group of argument.

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E.g. Max (1.0, 0.9, 0.8) will give 1.0 as 1.0 is maximum value among all. Min

Gives the minimum value in a group of argument. E.g. Max (1.0, 0.9, 0.8) will give 0.8 as 0.8 is maximum value among all.

Or

Returns TRUE if any of the conditions are TRUE. Otherwise, it returns FALSE. E.g. Or ( Cell A=‖INVALID‖, Cell B=‖INVALID‖) will give the outcome of TRUE if any of Cell A or B display INVALID or FALSE otherwise.

PI

Returns the value of pi (π).

Round

Provides arithmetic rounding for a value. E.g. Round (0.1102, 2) will give the outcome of 0.11 by rounding 0.1102 to 2 decimal places.

SIN

Returns the sine of a number (in radians). E.g. SIN (1.0) will give the outcome of 0.84 which is the sine of angle 1.0 radians.

TRUE

Returns a logical value TRUE.

Vlookup

Searches for the value in the left-most column of table_array and returns the value in the same row based on the index_number. E.g. VLookup( Cell A, B1:P100, 2,FALSE ) will pick up the number in column 2 of the B1:P100 array corresponding to Cell A exactly.

&

Returns the combination of value or text before and after ―&‖ E.g. CHS & 219.5x12.5 will give CHS 219.5x12.5.

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The functions mentioned were used in different ways in different combinations to give better flexibility in the design spreadsheets. Besides, array formula was used in creating the design spreasheets. Usually, ―Enter‖ key can be used to get the outcome of formula used in a particular cell. For array formula, users need to hold down the ―Ctrl‖ and the ―Shift‖ keys and then press ―Enter‖ to obtain the outcome of a particular cell. Besides the functions stated in Table 3-1, there were also other features used to enhance the flexibility of the design tool. In the Microsoft Excel, variables can be changed in a convenient way using the drop down list. The user can directly choose the options from the drop down list without the need of typing in the variables. This will ease the data input as errors might occur while typing in the exact input manually and this may cause misinterpretations. The drop down lists was created using the Data Validation under the Data ribbon in the Microsoft Excel. Under the Validation criteria, ―List‖ was allowed and the ―Source‖ is the content of the Drop down list. User can also insert command in the ―Source‖ in order to conditionally choose the content of drop down list based on the commands as shown in Figure 3-2.

Figure 3-2: Data Validation

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The Figure 3-3 shows the examples of the use of drop down list created for the types of CHS used for the CHS joints design. Other than section size, the section type and grade also have drop down list with different section and grade respectively.

Figure 3-3: Drop Down List in Spreadsheet

Other than that, another useful feature used in the spreadsheet was the Conditional Formatting feature. It enables the authors to easily highlight the important cells and stress on unusual values using Data Bars, Icon Scale and Icon sets based on criteria set. This feature is especially important to emphasize the outcome or the findings of the spreadsheet. Under the Home ribbon, the Conditional Formatting tab consists of some typical options of formatting as shown in Figure 3-4. Multiple rules can be applied onto a same cell for few possibilities of outcomes. The Figure 3-5 shows the conditional formatting rules manager where user can manage the rules created using Conditional Formatting.

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Figure 3-4: Conditional Formatting Options

Figure 3-5: Conditional Formating Rules Manager

The Figure 3-6 shows the use of the conditional formatting showing the result summary of the spreadsheet and emphasize on the interesting cells using different colours.

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Figure 3-6: Conditional Formatting feature in Microsoft Excel

Besides that, simple macro had been inserted into to the design spreadsheet. It was used to automatically clear the content when corresponding cell‘s variable is changed. The example of the code used is shown in the Figure 3-7.

Figure 3-7: Code used for macro

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3.2 Section and Joint Properties The properties listed in the Table 3-2 will be used in validity check and also in determining the joint strength. Table 3-2: Sections and joint properties (BSI 2005)

Properties

Explanations

d0

is the diameter of a chord member

di [i=1,2,3…]

is the diameter of a brace members

t0

is the thickness of a chord member

ti [i=1,2,3…]

is the thickness of a brace members

A

is the cross sectional area of a section

Ө

is the angle between a chord and a brace member

φ

is the angle between planes in multiplanar joint

fy0

is the yield strength of a chord member

fyi [i=1,2,3…]

is the yield strength of brace members

N*

is the design internal axial force in a member

Ni,Rd [i=0,1,2,3…]

is the design value of the resistance of the joint which is expressed in terms of the internal axial force in a member

Mip*

is the design in-plane moment in a member

Mip*

is the design out-of-plane moment in a member

Mip,i,Rd [i=0,1,2,3…]

is the design resistance of the resistance of the joint which expressed in internal in-plane moment in a member

Mop,i,Rd [i=0,1,2,3…]

is the design resistance of the resistance of the joint which expressed in internal out-of-plane moment in a member

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3.2.1 Joint Validity Checks The design of the CHS joints is valid provided that the geometry of the joints is within the range of validity given in the Table 3-3. As long as the joints are within the range of validity, only chord face failure and punching shear need to be considered in the joint design. As for the joints outside the range of validity as shown in Table 3-3, all the failure modes for hollow section joints need to be assessed. Also, the secondary moments in the joints which caused by their rotational stiffness should be considered as well (BSI 2005). Failure to check validity limits will often results in section sizes requiring changing at stage of fabrications. Thus, it is important for simple initial checks to keep all the sections chosen for chord and brace member within the validity range. Table 3-3: Range of validity for welded joints between CHS chords and braces members (T7.1 Eurocode 3-2005)

0.2 ≤ di/d0 ≤ 1.0 Class 2 and 10 ≤ d0/t0 ≤ 50 generally But 10 ≤ d0/t0 ≤ 40 for X joints Class 2 and 10 ≤ di/ti ≤50 λov ≥ 25% g ≥ t1 + t 2 (-0.55)d0 ≤ e ≤ 0.25d0

3.2.2 Design Factors and Parameters The factors and parameters used in calculating the design capacities (resistance) of CHS joints are shown in Table 3-4.

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Table 3-4: Design Factors and Parameters (BSI 2005)

Factors and Parameter

Explanations

γM5

is the partial safety factor for resistance of joints in hollow section lattice girder. It is taken as 1.0 for the design spreadsheet.

γ

is the ratio of the chord diameter to twice of its wall thickness where the formula is,

β

is the ratio of the mean diameter of the brace member to that if the chord 1.0 For T, Y and X joints,

2.0 For K and N joints,

3.0 For K and N joints:

g

is the gap between brace members at the face of the chord.

p

is the projected contact area length between the overlapping brace and the chord member without considering the overlapped member.

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q

is the overlap length between brace members

λov

is the overlap ratio

k

Factor of k in the subscript of g and p are used especially in calculating the design resistance of the chord face failure. kg is the gap/lap factor.

(

) (

*

kp is the CHS end load factor. but kp≤1.0

For np>0 (compression) : For np≤0 (tension): where np is the stress ratio used for CHS chords,

is the value of (maximum compressive stress in the chord) excluding the stress due to the members parallel to the chord axis of the axial forces in the braces at that particular joint. can be found using the formula below.

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where (

∑

.

is the maximum compressive force in the chord of a joint)

3.2.3 Assumptions Made Throughout the Design Process The following assumptions were made throughout the project: 1. The design spreadsheet for CHS joints was created in accordance with EC3. 2. The design tool is valid both for hot finished CHS and cold formed CHS. 3. The internal forces and moments are assumed to be in equilibrium 4. Each member in the joint was capable of resisting the internal forces and moments.

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3.3 Static Strength of Circular Hollow Section Joint: Eurocode 3 (BSI 2005) 3.3.1 T And Y Joints

Figure 3-8: T or Y Joint (Taken from BSI 2005)

3.3.1.1 Design Axial Resistance Check 1: Chord face failure (

)

Eqn 3-1

Check 2: Punching shear failure [i = 1, 2 or 3] When di ≤ d0 - 2t0: Eqn 3-2

√

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3.3.1.2 Design Moment Resistance Check 3: Chord face failure (In-plane Moment)

Figure 3-9: Chord face failure for in-plane moment (Taken from BSI 2005) √

Eqn 3-3

Check 4: Chord face failure (Out-of-plane Moment)

Figure 3-10: Chord face failure for out-of-plane moment (Taken from BSI 2005) Eqn 3-4

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Check 5: Punching shear failure When d1 ≤ d0 – 2t0:

Eqn 3-5

√

Eqn 3-6

√

3.3.2 X Joints

Figure 3-11: X joint (Taken from BSI 2005)

3.3.2.1 Design Axial Resistance Check 1: Chord face failure

Eqn 3-7

Check 2: Punching shear failure [i = 1, 2 or 3] Refer Eqn 3-2.

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3.3.2.2 Design Moment Resistance Check 3: Chord face failure (In-plane Moment) Refer Eqn 3-3. Check 4: Chord face failure (Out-of-plane Moment) Refer Eqn 3-4.

Check 5: Punching shear failure Refer Eqn 3-5and Eqn 3-6.

3.3.3 K And N Joints 3.3.3.1 Gap Joints Design Axial Resistance

Figure 3-12: Gapped K joint (Taken from BSI 2005)

Check 1: Chord face failure

Eqn 3-8

Eqn 3-9

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Check 2: Punching shear failure Refer Eqn 3-2.

Design Moment Resistance Check 3: Chord face failure (Out-of-plane Moment) Refer Eqn 3-4.

Check 4: Punching shear failure Refer Eqn 3-6.

3.3.3.2 Overlap Joints

Figure 3-13: Overlapped K joint (Taken from BSI 2005)

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Design Axial Resistance Check 1: Chord face failure Refer Eqn 3-8 and Eqn 3-9.

Design Moment Resistance Check 2: Chord face failure (Out-of-plane moment) Refer Eqn 3-4.

3.3.4 KT Joints

Figure 3-14: KT joint (Taken from BSI 2005)

3.3.4.1 Design Axial Resistance Check 1: Chord face failure Refer Eqn 3-8 and Eqn 3-9. Members 1 and 3 are here in compression and member 2 is here in tension

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where N1,Rd in Eqn 3-8 is the value of N1,Rd for a K joint but with

Check 2: Punching shear failure [i = 1, 2 or 3] Refer Eqn 3-2.

3.3.4.2 Design Moment Resistance Check 3: Chord face failure (Out-of-plane moment) Refer Eqn 3-4.

Check 4: Punching shear failure Refer Eqn 3-6.

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3.3.5 TT Joints TT joint with 60°≤ φ ≤ 90°where member 1 may be either tension or compression.

Figure 3-15: TT Joint (Taken from BSI 2005)

Appropriate reduction factor µ was applied in the design resistance for each relevant plane of the multiplanar joint. The design resistance for each relevant plane of multiplanar joint should satisfy the design criteria after using the reduced design resistances. The reduction factor for TT joints, Eqn 3-10

3.3.6 XX Joints

Figure 3-16: XX Joint (Taken from BSI 2005)

Brace members 1 and 2 can be either in compression or tension. N2,Ed/N1,Ed shall be negative if one member is in tension and another in compression.

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The reduction factor for TT joints, Eqn 3-11

The sign of N1,Ed and N2,Ed need to be considered at all the time and fulfil |N2,Ed| ≤ |N1,Ed|.

3.3.7 KK Joints

Figure 3-17: KK Joint (Taken from BSI 2005)

Member 1 in KK joint is always in compression and member 2 is always in tension. For the KK joint with the angle between relevant planes, 60°≤ φ ≤ 90°, the reduction factor, µ shall be 0.9 with the condition that it fulfils the expression below in a gapped joint.

[

]

[

]

Eqn 3-12

For a joint that subject to combined bending and axial force, the brace member should fulfill the

Eqn 3-13.

[

]

Eqn 3-13

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3.4 User Interaction of Design Tool 3.4.1 Design Spreadsheets There were 7 design spreadsheets created to design different geometry of CHS joints. Some of joints that shared the same procedure were combined together. For example, T and Y joints as well as K and N joints. The 7 spreadsheets created are as follows: 1. T and Y Joints 2. X Joints 3. K and N Joints 4. KT Joints 5. TT Joints 6. XX Joints 7. KK Joints

3.4.2 Data input on the main page Users need to input the design data in the data input cells provided. Firstly, user needs to choose the type of steel used for members. The user will then need to choose the grade of the section used before they can choose the section size for chord and braces members. The angle between chord and braces members, ϴ needs to be inserted for each brace. Axial forces, N* acting on the joint for each members need to be clearly identified. Positive forces represent compression and negatives forces represent tension forces. The user will need to identify the moment (if any) either in-plane moment, Mip*or out-of-plane moment, Mop*. The partial factor for hollow section is stated as 1.0 in the Eurocode 3, Table 2.1 (BSI 2005). Detailed joint information such as the brace member gap (g), projected length (p), overlap length (q) and eccentricity (e) are then inserted if applicable as shown in Figure 3-18.

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Figure 3-18: Typical Data Input Table in Design Spreadsheets

3.4.3 Result Summary The result summary on the main page will show up the summarized results for the joint. The summary will either show up VALID, INVALID, OK, NOT OK or N/A for the checks as shown in Figure 3-6 earlier. The consequence pages show the detailed calculation of the joint if user wanted to look into it in case of failure (INVALID or NOT OK). In the detailed calculation part, Section 3 in design spreadsheets shows the section properties based on the sections chosen earlier. Sample of design spreadsheets can be found in Appendix B.

3.4.4 Detailed Checking Calculations Section 4 in the design spreadsheets (validity checks) examines on the geometry limits of the joint in order to comply with the formulae provided in the Eurocode. The checks include diameters ratio (di/d0), diameter and thickness ratio (d0/t0, di/ti), the angles between chord and braces (ϴ), the overlap ratio, λov, g and eccentricity (e). Section 5 in design spreadsheets shows the all the parameters and factors involved in the joint capacity (resistance) checking. When the design passes all the validity checks, the design check continues with checking on the axial resistance as well as moment resistance (if any) of the joint in section 6 and 7 respectively in design spreadsheets. Utilization ratio is used to compare the design capacity and resistance of the joint. The check will only appear as ―OK‖

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when the utilization ratio is less than 1. The same applies for moment resistance checks. Chord face failure check is check for both axial and moment resistance. Punching shear failure check is checked based on its failure criteria. Otherwise, it will appear as ―N/A‖ which represents that the punching shear is not critical in that particular joint. Refer Appendix B for the sample of design spreadsheet created for each CHS joints.

3.5 Verification Worked Examples and Case Studies 3.5.1 SHS Joint Worked Examples by Corus Tubes Corus is a subsidiary of Tata Steel, one of the world leading steel tube producers that produce hot finished and cold formed structural hollow sections production for over 25 years (Tata Steel 2011). Corus supply a range of branded tubes named Celcius 355, Hybox 355 and Strongbox 235 (Tata Steel 2011). Corus are actively supporting design engineers through this transition period by publishing steel building guidance documentation. One of the design guidance provided is worked examples on hollow sections joints. This design of structural hollow sections joints examples included the examples for both CHS and RHS joints design and checking. For CHS joints, worked examples on both gap and overlap K joints can be found. Verification was done based on the scenario provided in the worked example. Values were inserted into the design tool created to compare the outcome from the design tool and from the worked examples. The worked examples examined on the parameter limits and then the failure modes of CHS joints. Chord face deformation and chord punching shear failure were checked to ensure the adequacy of joint capacity. Compression and tension member were identified for calculation of joint capacity. In this worked example, brace 1 usually designated compression and brace 2 was under tension. Corus used two methods in finding the gap or lap function f (g) or kg in Eurocode and also the CHS chord end load function f (np) or kp in Eurocode. The two method used were using formulae and using graph. The formulae used were identical with formulae provided in Eurocode. The functions and factors were obtained using graphs according to the related parameters. The least calculated joint capacity for each brace was dictated by failures respectively.

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3.5.2 Design Handbook for RautaRuukki Structural Hollow Sections Verification was done based on the worked examples extracted from the Design Handbook for Rautaruuki Structural Hollow Sections (Oyj & Vainio 2000). The design handbook provided design guides in accordance with the Eurocode 3. The examples were presented in a similar way as Corus worked examples. Design examples on CHS T-joints subjected to bending was shown in the handbook. Besides, there were also examples of the T or Y joints, and X joints. The gap or lap factor,kg and also the CHS chord end load factor, kp were calculated using formulae in accordance with Eurocode 3. However, there is a minor difference where this design handbook adopted partial factor for resistance of cross-sections, γM0 as 1.1. This could be due to the earlier version of Eurocode they were adopting.

3.5.3 Worked Examples for the Design of Steel Structures (BRE, SCI, Arup) The worked examples included in this publication were design guide of the design of steel structures based on Eurocode 3. This was a publication done by the Building Research Establishment, BRE, the Steel Construction Institute, SCI and Ove Arup & Partners. BRE is the principal organization in the UK which carries out researches on technical aspects of building and other forms of construction related (BRE, SCI, Ove Arup & Partners 1994). SCI is an institute that aims to promote the proper and effective use of steel in construction while Ove Arup & Partners is an international firm that offer broad range of design and specialist services for the structure construction industry. This publication was first published in year 1994 and it provided a wide range of design worked examples for steel structures. One of the worked examples that related to CHS joints was the design of 30m span roof truss. This example covered the design of single-span roof trusses at 9-m centres. This example showed the design of the truss by angles and tees as well as using hollow sections. The front part of this example shows the member design of the truss. The steps are then followed by checking the efficiency of the joint. Members labelled with 6, 7, 11 and 12 in Figure 4-11 of Case 6 in Section 4.6 formed a gapped K joint with 12mm gap and other details as shown in the figure. The author first checked the joint geometry to ensure that the geometry limitations are fulfilled. The author checked the member capacities before started on checking the joint capacity. In the joint

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capacity checking, the author examined the chord plastification and punching shear failure of the N joint for both compression(member 12) and tension( member 11) members. The author considered the joint strength as the least value of the chord plastification and the punching shear values. Table 3-5 shows the summary of all the verification case studies and their sources. Table 3-5: Type of joints and verification sources

Case

1

Type of

Type of

Joints

Loading

Verification Source

Axial and

Design

Moment

Hollow Sections (Oyj & Vainio 2000)

T joints

Design 2

T joints

Axial

X joints

Axial

Gapped K 4

Joints

Joints

Axial

Joints

RautaRuukki

Structural

Structural

Handbook

for

RautaRuukki

Structural

Hollow Sections (Oyj & Vainio 2000)

(Morris 2006)

SHS Joints Worked Example by Corus Tubes Axial

Gapped N 6

for

RautaRuukki

SHS Joints Worked Example by Corus Tubes

Overlapped K 5

Handbook

for

Hollow Sections (Oyj & Vainio 2000)

Design 3

Handbook

(Morris 2006)

Worked Examples for the Design of Steel Structures Axial

(BRE, SCI & Arup 1994)

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4.0 RESULTS AND DISCUSSIONS The spreadsheets for Circular Hollow Section (CHS) ‗T and Y Joints‘, ‗X Joints‘, and ‗K and N Joints‘ created were verified by comparing the results with the case studies when identical scenario was applied. There are six cases with different scenarios used for verification of the spreadsheet in order to ensure the accuracy of the design spreadsheets.

4.1 Case 1: T Joint with Axial and Moment Loading T Joint with Axial and Moment Loading based on the Design Handbook for RautaRuukki Structural Hollow Sections (Oyj & Vainio 2000)

Figure 4-1: T joint under axial and moment loading - Case 1 (Taken from Oyj & Vainio 2000)

4.1.1 Input Data Table 4-1: Data input for Case 1

Chord Data Section Size Grade Chord and brace angle, ϴ (ᵒ) Axial Force, N* (kN) In-plane (kNm)

Moment,

Design Spreadsheet

RautaRuuki

Brace 1 Design Spreadsheet

RautaRuuki

CHS219.1 x5

CHS219.1 x5

S 355

S 355

-

90

273

70

-

30

Mip*

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4.1.2 Results and Discussions Validity Check Table 4-2: Validity Check for Case 1

Check

RautaRuuki

Design Spreadsheet

di/d0

-

VALID

d0/t0

-

VALID

di/ti

-

VALID

ϴ

-

VALID

Axial and Moment Resistance Check Table 4-3: Axial and Moment Resistance Check for Case 1

Brace 1 RautaRuuki Axial Resistance Check

Capacity

Forces (kN)

Joint N1,Rd

Capacity,

Failure Joint N1,Rd

Capacity,

Chord Face Failure Check Punching Check

Shear

Design Spreadsheet Forces

Ratio

(kN)

Ratio

230

0.30 (OK)

256

0.28 (OK )

N/A

N/A

N/A

N/A

Brace 1 RautaRuuki Moment Resistance Check

Capacity

Moment (kNm)

Joint Mip,Rd

Capacity,

Failure Joint Mop,Rd

Capacity,

Chord Face Failure Check Punching Check

Shear

Ratio

Design Spreadsheet Moment (kNm)

Ratio

36

0.80 (OK)

40

0.74 (OK )

N/A

N/A

N/A

N/A

Discussion This worked example adopted the same section for both the chord and brace members as shown in Table 4-1. It is a pure T joint as the angle between chord and brace is 90ᵒ. The joint members are loaded with axial forces and bending as shown in Figure 4-1. Both members are

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loaded in compressive axial loading. Detailed information on this worked example can be found in Appendix A1 whereas full design calculation set of spreadsheet can be found in Appendix B1. Validity check was carried out and the joint reached the ultimate loads either by chord face failure or punching shear failure as shown in Appendix B1. Since the diameter of brace member (d1) greater than subtraction of diameter of chord with two times of chord thickness (d0 – 2t0), the chord punching shear did not be taken into consideration for calculating both axial and bending resistance. Hence, ―N/A‖ was shown for part involving punching shear calculation. Design resistance of a joint is the maximum or ultimate design axial or moment resistance for brace members. In most of the case, a joint is considered sufficient provided that all brace members have greater design capacity (resistance) if compared to design forces acting onto the joint. The utilization ratio had been calculated for all the brace members involved. Utilization ratio is the ratio of design action (loadings act onto the joint) and its joint design capacity (resistance). This ratio shows the amount of capacity utilized by a joint in this context. Hence, whenever it is less than 1.0, a joint is not critical and said to be sufficient. When the ratio exceeds 1.0, the joint is not able to resist and cater the loading acted on the joint. Thus, the design of the joint is failed. The result showed that all utilization ratios were less than 1.0 as shown in Table 4-3. Thus, the design of joint was sufficient. From the comparison, the design spreadsheet gave a higher value of joint capacity for both axial and moment resistance checks. This is due to the difference in the partial safety factors used for resistance of joints in hollow section lattices. The partial safety factor used in the design example is slightly different with the partial safety factor used in design spreadsheet. The partial safety factor used in design example is whereas the partial safety factor used in the design spreadsheet is

. Both of the partial

safety factors for Class 1, 2 and 3 cross-sections, ɣM0 and partial safety factor for resistance of joints in hollow section lattices are adopted as 1.1. This could be due to use of earlier version of EC3. This made the expression of

to

and hence gives 0.909. On the other hand,

the design spreadsheet adopted the partial safety factors for joints in hollow section lattice girder ɣM5 as 1.0 (Table 2.1 EC3). Hence, the outcomes of design spreadsheet will always be slightly greater if compared to values in the worked example provided by Oyj & Vainio

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(2000). The partial safety factor will affect in finding the CHS chord end load factor, np. The np obtained will then affect the kp factor and hence lowered the joint capacity (resistance). This shows that the design code adopted by Oyj & Vainio in this design is more conservative as compared to the Eurocode 3 – 2005 adopted by design spreadsheets. For connection subjected to both axial and bending, the brace member connections subject to combined bending and axial force should fulfill the Eqn 3-13. From the design spreadsheet, the value obtained for Eqn 3-13 is 0.82 which was less than 1.0. So, the combined bending and axial force is not critical in this case.

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4.2 Case 2: T Joint with Axial Loading T Joint with Axial Loading based on the Design Handbook for RautaRuukki Structural Hollow Sections (Oyj & Vainio 2000)

Figure 4-2: T joint under axial loading - Case 2 (Taken from Oyj & Vainio 2000)

4.2.1 Input Data Table 4-4: Data input for Case 2

Chord Data

Design Spreadsheet

RautaRuuki

Section Size Grade

RautaRuuki

Design Spreadsheet

CHS219.1 x10

CHS168.3 x5

S 355

S 355

-

90

1018.2

450

Chord and brace angle, ϴ (ᵒ) Axial Force, N* (kN)

Brace 1

4.2.2 Results and Discussions Validity Check The Validity Check is similar to Table 4-2 in Case 1.

Axial Resistance Check Table 4-5: Axial Resistance Check for Case 2

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Brace 1 RautaRuuki Check

Capacity

Forces (kN)

Chord Face Failure Check

Ratio

Design Spreadsheet Forces (kN)

Ratio

Joint Capacity, N1,Rd

462

0.97 (OK)

520

0.87 (OK )

Punching Shear Failure Check Joint Capacity, N1,Rd

985

0.46 (OK)

1087

0.42 (OK )

Discussion A similar way of verification had been done for a T joint which is loaded under axial only. The section used for chord and brace members are different in this case. The brace member was smaller than the chord member used as illustrated in Figure 4-2. Both members were loaded under compressive forces. Detailed information on this worked example can be found in Appendix A2 whereas full design calculation set of spreadsheet can be found in Appendix B2. This joint passes all the range of validity as shown in Table 4-3. Hence, only chord face failure and punching shear failure needed to be considered. Both chord face failure and punching shear checks were carried out for this joint. As the diameter of brace member (d1) is less than subtraction of diameter of chord with two times of chord thickness (d0 – 2t0), the chord punching shear need to be taken into consideration in determining axial resistance. Axial resistance in this case is governed by the chord face failure as it gave lower resistance as compared to punching shear. The result showed that all utilization ratios were less than 1.0. Thus, the design of joint was sufficient. From comparisons in Table 4-5, joint capacity (resistance) obtained by Oyj & Vainio was again lower than the resistance calculated in design spreadsheet. This was due to the same reasons as explained in Case 1. Since the outcomes agreed well each other, ―T and Y Joints‖ spreadsheet was verified. By comparing Case 1 and Case 2, the results showed that reduce in the chord width to thickness ratio (γ) gave an increase in the joint capacity. Case 1 with high γ value (21.9) had the joint capacity (resistance) of 256kN only. In contrast, Case 2 with low γ value (11.0) had the joint capacity (resistance) of 520kN which was almost double of joint capacity in Case 1.

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Therefore, it is more recommended to adopt a smaller, thicker chord to gives a low γ value as mentioned in Section 2.4.4 earlier on. Testing was done by altering the input for this design spread using a smaller diameter brace with a larger diameter chord to give a smaller bracing diameter to chord diameter ratio (β). The outcome of the testing showed that larger β value (Case 2) resulted in higher joint capacity. Therefore, it was more recommended to adopt a larger diameter section for brace and smaller diameter for chord to gives a higher β value for a higher joint capacity. Besides, the bracing angle, θ also affected capacity of a joint. Case 2 showed a pure T joint with θ=90o. As mentioned in Section 2.4.4, smaller bracing angle will results in higher joint capacity (resistance). By changing the bracing angle into say 30o, the joint became a Y joint instead of the T joint. The capacity increased dramatically from 520kN to 1150kN. The capacity was increasing when the bracing angle was decreasing. This could be due to the reason that the net force acting onto the joint as compared to those acting normal to the chord.

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4.3 Case 3: X Joint with Axial Loading X Joint with Axial Loading based on the Design Handbook for RautaRuukki Structural Hollow Sections (Oyj & Vainio 2000)

Figure 4-3: X joint under axial loading - Case 3 (Taken from Oyj & Vainio 2000)

4.3.1 Input Data Table 4-6: Data input for Case 3

Chord Data Section Size Grade

Design Spreadsheet

RautaRuuki

CHS219.1 x10

CHS193.7 x6.3

S 355

S 355

-

90

1018.2

450

Chord and brace angle, ϴ (ᵒ) Axial Force, N* (kN)

Design Spreadsheet

RautaRuuki

Brace 1

4.3.2 Results and Discussions Validity Check The Validity Check is similar to Table 4-2 in Case 1.

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Axial Resistance Check Table 4-7: Axial Resistance Check for Case 3

Brace 1 RautaRuuki Check

Capacity

Forces (kN)

Joint N1,Rd

Capacity,

Failure Joint N1,Rd

Capacity,

Chord Face Failure Check Punching Check

Shear

Ratio

Design Spreadsheet Forces (kN)

Ratio

467

0.96 (OK)

528

0.85 (OK )

1134

0.40 (OK)

1247

0.36 (OK )

Discussion This example worked on an axial loaded X joint. The angle between its chord and member is 90ᵒ and both members are in compression as illustrated in Figure 4-3. The size of the section used for chord and brace were different. Detailed information on this worked example can be found in Appendix A3 whereas full design calculation set of spreadsheet can be found in Appendix B3. As the joint geometry passed all the relevant validity check (refer Table 4-3), only chord face and punching shear failure needed to be considered. There was need to check on punching shear failure for this case as well because the diameter of brace member (d1) is less than subtraction of diameter of chord with two times of chord thickness (d0 – 2t0). Chord face failure again governed the axial resistance as it has lower value as compared to punching shear. The result showed that all utilization ratios were less than 1.0 as shown in Table 4-7. Thus, the design of joint was sufficient. Same reasons apply for this case for getting a different joint resistance for worked examples and design spreadsheet. Hence, this case had verified the ―X Joint‖ spreadsheet.

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Testing was done by altering the input in this design spreadsheet. Lower γ value and higher β value both gave high joint capacity (resistance) as discussed in Case 2. A smaller bracing angle, θ resulted in a high joint capacity as well.

4.4 Case 4: Gapped K Joint with Axial Loading Gapped K Joint with Axial Loading based on the SHS Joints Worked Example by Corus Tubes (Morris 2006)

Figure 4-4: Gapped K joint under axial loading - Case 4 (Taken from Morris 2006)

4.4.1 Input Data Table 4-8: Data input for Case 4

Chord

Data Corus Section Size Grade Chord and brace angle, ϴ (ᵒ) Axial Force, N* (kN)

Brace 1

Design Spreadsheet

Corus

Design Spreadsheet

Brace 2 Corus

Design Spreadsheet

CHS219.1 x12.5

CHS139.7 x5

CHS114.3 x3.6

S 355

S 355

S 355

-

45

45

1636

500

-400

Brace member gap, g (mm)

40

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4.4.2 Results and Discussions Validity Check Table 4-9: Validity Check for Case 4

Check

Corus

Design Spreadsheet

di/d0

PASS

VALID

d0/t0

PASS

VALID

di/ti

PASS

VALID

ϴ

PASS

VALID

g

PASS

VALID

Axial Resistance Check Table 4-10: Axial Resistance Check for Case 4

Brace 1 Design Spreadsheet

Corus Check

Capacity

Forces (kN)

Brace 2

Ratio

Forces (kN)

Ratio

Corus Forces (kN)

Ratio

Design Spreadsheet Forces (kN)

Ratio

Joint Chord Face Capacity, Failure Check N1,Rd

986

0.51 (OK)

986

0.51 (OK )

986

0.41 (OK)

986

0.41 (OK )

Joint Punching Shear Capacity, Failure Check N1,Rd

1919

0.18 (OK)

1919

0.18 (OK )

1570

0.18 (OK)

1570

0.18 (OK )

Discussion In this case, the worked example was done by the Morris, Corus Tubes (2006). This worked example illustrated an example of gapped K joint under axial loading (Figure 4-4). The section used for chord and braces were different with each other. The chord and brace 1 was loaded under compressive loading while brace 2 was under tension. The chord and brace angle, ϴ are 45ᵒ. No eccentricity found in this example. Detailed information on this worked

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example can be found in Appendix A4 whereas full design calculation set of spreadsheet can be found in Appendix B4. The gap between brace members, g must be greater than the sum of thickness for both chord and brace member to ease the welding of brace members onto chord members. The gap between brace members, g was defined as shown in the Figure 4-5.

Figure 4-5: Definition of gap, g (Taken from BSI 2005)

This worked example showed a clear and precise parameter limits check. The parameters all passed the limit (validity) checks in both worked example by Morris and the design spreadsheet. The joint reached the ultimate loads either by chord face failure or punching shear failure as all the parameters were within the validity range. All utilization ratios obtained were less than 1.0. Thus, the design of joint was adequate. Comparison was done on the axial resistance calculated for both sides; Morris‘s worked example and the design spreadsheet. The axial resistances calculated for chord face failure in both braces are lesser than punching shear and hence it governs the axial resistance in this case again. The axial resistance by chord face failure and punching shear for both sides are totally identical. In this worked example, the author has shown two method of finding the gap or lap function, kg and the CHS chord end load function, kp. The first method was using the formulae provided in EC3 -2005. The second method used was using graph as shown in Figure 4-6 and Figure 4-7. Both methods turned out to have a same value for factor of kg and kp. Joint capacity dictated by chord face failure for both bracings as the capacity calculated

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are both lower than punching shear capacity (resistance). Hence, it can be said that chord face failure is more critical than punching shear failure at most of the time. A gap joint are generally preferable to an overlap joint. The reason is that the braces are easier to prepare, fit, and weld onto its chord. This will result in an economic fabrication as it is easier and cheaper to assemble the joint as shown in Figure 4-8. Simple fillet weld can be used around the full circumference of CHS as long as there is sufficient gap or clearance between brace members. Nevertheless, gapped joint may results in eccentricity. The eccentricity issue will be further discussed in Case 5 and 6 as this case did not show eccentricity.

Figure 4-6: Chord end load function for CHS joints (Taken from Corus Tubes 2005)

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Figure 4-7: Gap/lap function for CHS joints (Taken from Corus Tubes 2005)

Figure 4-8: Economics of Welded Joints (adapted from Whitfield & Morris 2009)

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4.5 Case 5: Overlapped K Joint with Axial Loading Overlapped K Joint with Axial Loading based on the SHS Joints Worked Example by Corus Tubes (Morris 2006)

Figure 4-9: Overlapped K joint under axial loading - Case 5 (Taken from Morris 2006)

4.5.1 Input Data Table 4-11: Data input for Case 5

Chord Data

Corus

Section Size Grade Chord and angle, ϴ (ᵒ)

brace

Axial Force, N* (kN)

Brace 1

Design Spreadsheet

length,

Design Spreadsheet

Corus

Design Spreadsheet

CHS219.1 x12.5

CHS139.7 x5

CHS114.3 x3.6

S 355

S 355

S 355

-

45

45

1636

500

-400

Projected length, p (mm) Overlap (mm)

Corus

Brace 2

161.64

q

45

Eccentricity, e (mm)

-42.2

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4.5.2 Results and Discussions Validity Check Table 4-12: Validity Check for Case 5

Check

Corus

Design Spreadsheet

di/d0

PASS

VALID

d0/t0

PASS

VALID

di/ti

PASS

VALID

ϴ

PASS

VALID

λov

PASS

VALID

Eccentricity, e

PASS

VALID

Axial Resistance Check Table 4-13: Axial Resistance Check for Case 5

Brace 1 Check

Capacity

Design Spreadsheet

Corus Forces (kN)

Brace 2

Forces

Ratio

(kN)

Ratio

Corus Forces (kN)

Ratio

Design Spreadsheet Forces (kN)

Ratio

Joint Capacity, N1,Rd

1134

0.44 (OK)

1133

0.44 (OK )

1134

0.35 (OK)

1133

0.35 (OK )

Punching Joint Shear Failure Capacity, Check N1,Rd

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

Chord Face Failure Check

Discussion This case showed the scenario of an overlapped K joint under axial loading. The geometry of the joint was very similar with Case 4 except that it was an overlapped K joint and it was a gapped K joint in Case 4. Besides this difference, there was negative eccentricity (e) of 42.2mm in this overlapped K joint as illustrated in Figure 4-9 . Negative eccentricity can be defined as shown in Figure 4-13(c). Detailed information on this worked example can be

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found in Appendix A5 whereas full design calculation set of spreadsheet can be found in Appendix B5. The eccentricity needed to be checked so that it is within the range of validity. The eccentricity was within the range of (-0.55) d0 ≤ e ≤ 0.25d0. Therefore, moment due to joint eccentricity was not considered in this joint. Detailed information on eccentricity will be discussed in Case 6. The validity check for all the parameter limits were checked in both worked example and design spreadsheet. Besides eccentricity, the overlap ratio (λov) for overlap joint was checked. It was calculated by taking the ratio percentage between overlap length (q) and projected length (p),

. The overlap length, q and projected

length, p can be found by referring the Figure 4-10. The overlap ratio should not greater than 25% in order to avoid other failure mode such as brace local buckling failure modes as the formulae provided were cater for chord face failure and punching shear failure only.

Figure 4-10: Definition of overlap ratio (Taken from BSI 2005)

The result presented that all utilization ratios were less than 1.0 as shown in Table 4-13. Consequently, the design of joint was adequate. Chord punching shear check was not required for overlapped joints and therefore the joint capacity is governed by chord face failure for both braces. By comparing Case 4 and 5, the sections size used are identical. However, capacities for both cases were different. Case 5, overlap K joint had a higher joint capacity although the sections used are identical with Case 4. Thus, a

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By altering the input used in the design tool, the strength of the overlap K joint increased as overlap increased. This was due to the load transfer from overlapping brace to overlapped brace and hence fewer loads acting onto the joint and hence resulted in increased joint capacity (resistance). In the case when the overlap ratio is greater than the validity limit, the local buckling of the compression brace could become more critical. And therefore, the two failure modes, chord face failure and brace local buckling failure modes will interact with each other and dictate the joint capacity (resistance). However, fabrication costs for 100% overlap joints is less than that of the partial overlap joints as shown in Figure 4-8. This could be due to preparation of edges of welding in partial overlap joints are complicated than the 100% overlap joints. Reducing chord diameter to thickness ratio (γ), increasing brace diameter to chord diameter ratio (β), and reducing bracing angle (θ) were valid in increasing joint capacity for overlap K joint as well. Besides, there were some other recommendations that could be applied on overlap joint to increase joint capacity. A smaller, thicker with higher yield strength overlapped brace could be adopted. Other than that, a thicker with higher yield strength chord compared to the overlapped bracing could help in increasing joint capacity as well.

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4.6 Case 6: Gapped N Joint with Axial Loading Gapped N Joint with Axial Loading based on the Worked Examples for the Design of Steel Structures (BRE, SCI & Arup 1994)

Figure 4-11: N joint under axial loading - Case 6 (Taken from BRE, SCI, Ove Arup & Partners 1994)

4.6.1 Input Data Table 4-14: Data input for Case 6

Chord Data

Arup

Section Size Grade Chord and angle, ϴ (ᵒ)

brace

Axial Force, N* (kN)

Brace 1

Design Spreadsheet

Arup

Design Spreadsheet

Brace 2 Arup

Design Spreadsheet

CHS193.7 x8

CHS114.3 x5

CHS88.9 x5

S 275

S 275

S 275

-

37.8

90

-258

-323

194

Brace member gap, g (mm)

12

Eccentricity, e (mm)

39

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4.6.2 Results and Discussions Validity Check Table 4-15: Validity Check for Case 6

Check

Arup

Design Spreadsheet

di/d0

SATISFACTORY

VALID

d0/t0

SATISFACTORY

VALID

di/ti

SATISFACTORY

VALID

ϴ

-

VALID

g

-

VALID

Eccentricity, e

-

VALID

Axial Resistance Check Table 4-16: Axial Resistance Check for Case 6

Brace 1 Design Spreadsheet

Arup Check

Capacity

Forces (kN)

Brace 2

Forces

Ratio

(kN)

Ratio

Arup Forces (kN)

Ratio

Design Spreadsheet Forces (kN)

Ratio

Chord Face Joint Failure Capacity, Check N1,Rd

517

0.63 (OK)

483

0.67 (OK )

197

0.99 (OK)

296

0.66 (OK )

Punching Joint Shear Failure Capacity, Check N1,Rd

641

0.50 (OK)

979

0.20 (OK )

372

0.52 (OK)

355

0.55 (OK )

Discussion This case study was chosen to verify the N joints design spreadsheet. This design example was done by the BRE, SCI and Ove Arup & Partners. The joint design example was actually extracted from part of the roof truss design as shown in Figure 4-12.

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Figure 4-12: Outline of 30m span truss (Taken from BRE, SCI, Ove Arup & Partners 1994)

The gapped N joint in Figure 4-11 is the connection between member 6, 7, 11 and 12 as shown in Figure 4-12. The front part of the design included the CHS member design and continues with joint checking. Both chord (6, 7) and brace 1(11) were under tension and brace 2 (12) was under compression. Detailed information on this worked example can be found in Appendix A6 whereas full design calculation set of spreadsheet can be found in Appendix B6. Gap joints will usually cause eccentricity and secondary bending. However, the eccentricity is acceptable in joint design if the intersection of the centre lines of brace members lies within the valid range measured from the centre line of the chord member. The valid range is in between 25% of chord diameter towards the outside of joint (positive eccentricity) as shown in Figure 4-13(b) and 55% of chord diameter towards in inner side of the joint (negative eccentricity) as shown in Figure 4-13(c). This can be expressed in -0.55d0 ≤ e ≤ 0.25d0.

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Figure 4-13: Influence of gap and overlap on eccentricity (modified from Whitfield & Morris 2009)

As long as it passed this valid range and all other geometrical limits, the effects of eccentricity were taken into account in the joint design formulae. However it is always recommended to keep eccentricities to minimal. Also, the secondary moments due to joint stiffness will not affect the resistance (capacity) of the joint for the joint that satisfied all the geometrical limits provided in Table 3-3 of Section 3.2.1. In the initial design stage, zero eccentricity was assumed due to the use of wire frame. It will be ideal to have zero eccentricity as eccentricities results in additional moments. Hence, zero eccentricity is recommended to be the starting point and only then geometry will control whether the joint is a gap or overlap joint. In some case when gap or overlap validity checks are considered, there might be necessary to introduce little joint eccentricity in order to pass the gap or overlap validity checks. The condition is that the eccentricity introduce have to be kept within the parameter limit mentioned earlier. If the eccentricity limit did not met at the first place, secondary moments due to eccentricity need to be taken into consideration in the joint design. Therefore, gap and overlap validity checks in this case have priority over eccentricity limits. A positive eccentricity of 39mm was found in this case. It was within the valid range of 0.55d0 ≤ e ≤ 0.25d0 and hence, this eccentricity will not influence the joint capacity (resistance). The example did not show the validity check for the gap and eccentricity. The design spreadsheet checked all the parameters limits and all passed. Hence, the joint reached the ultimate loads either by chord face failure or punching shear failure. The checking was then

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proceeded to check the axial resistance of the joint. Since the diameter of brace member (d1) was less than subtraction of diameter of chord with two times of chord thickness (d0 – 2t0), the chord punching shear needed to be taken into consideration for determination of joint strength. The result showed that all utilization ratios were less than 1.0. Thus, the design of joint was sufficient. From comparison as shown in Table 4-16, the design spreadsheet again showed up with greater value as compared to the case study. This difference was looked into by referring the steps in detailed. One of the reasons was due to the partial safety factor used. The other reason is that the formula used to obtain the joint capacity (resistance) for brace 2 are different. Eurocode 3-2005 suggested the ratio of the bracing angles to calculate the capacity for Brace 2 (Eqn 3-9) whereas the work example used Eqn 3-8 to calculate the capacity for Brace 2 This work example probably adopted an earlier version of EC3 instead of the 2005 version. Hence, it can be said that the Eurocode 3 adopted by BRE, SCI, Ove Arup & Partners was more conservative than the Eurocode 3 version 2005. Chord face failure once again governed the joint capacity. The outcomes from design spreadsheets were in good agreement with the Case 4, 5 and 6. Thus, this had verified the ―K and N Joints‖ Design Spreadsheet. Testings were done by altering the input in this ―K and N Joints‖ Design Spreadsheet. Lower γ value and higher β value both gave high joint capacity (resistance) as discussed in Case 2. A smaller bracing angle, θ resulted in a high joint capacity as well. Also, joint capacity decreased when the gap between braces increased. So, it is recommended to provide minimum gap distance to maximize the joint capacity.

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4.7 KT Joint There was no case study found to verify the ―KT Joint‖ Design Spreadsheet. ―KT Joint‖ Design Spreadsheet was created in a similar way of creating ―K and N Joint‖ Design Spreadsheet. Since ―K and N Joint‖ Design Spreadsheet was verified by Case 4, 5 and 6, it was assumed that ―KT Joint‖ Design Spreadsheet was verified also.

4.8 Multiplanar Joints The behavior of multiplanar CHS joints is similar to the corresponding uniplanar. Eurocode 3-2005 suggested that a reduction factor needed to be applied when calculating the joint capacity (resistance). Therefore, design engineers could easily identify the behavior of CHS multiplanar joints and relations between loads in different planes. It is recommended to design multiplanar joints that satisfied the validity range suggested in Table 3-3 as the behavior of multiplanar joints are very similar to those of their uniplanar counterpart.

TT Joint As mentioned in Section 2.2.2, the capacity (resistance) of multiplanar T joint, TT joint did not vary substantially if compared to the uniplanar T joint. Hence, the reduction factor of 1.0 was suggested in Eurocode 3-2005. This means that the capacity (resistance) of the multiplanar joint is equal to that of its uniplanar joint respectively. Design spreadsheet f for TT joint was created. A set of design spreadsheet was included in Appendix B8 using the input from Case 2. The outcomes from the design spreadsheet were identical with case. Since the ―T an Y joints‖ spreadsheet was verified earlier, the TT joint was assumed to be verified also.

XX Joint Also mentioned in Section 2.2.2, multiplanar effects are most significant for XX joint. The multiplanar loading onto the joints give significant effects on the strength and stiffness if

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compared to a uniplanar X joint. Members 1 and 2 can be either in compression or tension. N2,Ed/N1,Ed is negative if one member is in tension and one in compression. The reduction factor is calculated using this formula. μ = 1 + 0.33N2,Ed/N1,Ed (Eqn 3-11) where modulus of N2,Ed should less than or equal to that of N1,Ed. When both X braces on both planes were loaded with same magnitude but opposite sense (compression and tension), the strength decreased by about 33 percent of its uniplanar joint capacity (resistance). In contrast, the joint capacity increases significantly when the joint were loaded with the same sense. This may due to the nett forces applied to multiplanar joint are minimal when the sense of loading are same. Forces canceled out each other and hence less forces act onto the joint which gives a higher capacity or resistance. A conservative assumption had been made in Eurocode that the capacity will also increase by around 33% in the case of same loading sense for both braces of joint in both planes. A set of design spreadsheet was included in Appendix B9 using the input from Case 3. The outcomes of design spreadsheet showed slight differences with case study. This is due to the reduction factor applied onto the joint capacity for its uniplanar counterpart. In both K1 and K2 planes were loaded with same magnitude and same sense of loading. Both braces in both planes are loaded in compression. Therefore, it gave the reduction factor of 1.33 and the joint capacity increased by 33% if compared to its corresponding uniplanar joint capacity (resistance). Since the ―X joints‖ spreadsheet was verified earlier, the ―XX Joint‖ Design Spreadsheet was assumed to be verified also.

KK Joint Eurocode 3-2005 suggested reduction factor of 0.9 for multiplanar KK joint provided that the KK is a gap-typed KK joints satisfies Eqn 3-12 in Section 3.3.7. Member 1 should always in compression and member 2 is always in tension as shown in Figure 3-17. This is conservative as compared to CIDECT design guides as CIDECT were suggesting the correction (reduction) factor of 1.0 instead of 0.9.

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A set of design spreadsheet was included in Appendix B10 using the input from Case 5. The outcomes of design spreadsheet showed minor differences with case study. This is due to the reduction factor applied onto the joint capacity for its uniplanar counterpart. Since the ―K joints‖ spreadsheet was verified earlier, the ―KK Joint‖ Design Spreadsheet was assumed to be verified also.

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5.0 CONCLUSIONS AND RECOMMENDATIONS The design rules for Circular Hollow Sections (CHS) joints had been reviewed and studied. Design spreadsheets have been created in the Microsoft Excel in accordance with Eurocode 3. The important design considerations such as parameter limits or the validity check have been included in the design spreadsheets. This check is important to determine modes of failure which are critical. They are usually only chord face failure and punching shear failure need to be considered. For any joints that did not pass the validity checks, all the six failure modes should be considered. Considerations and parameter affecting design capacities (resistances) need to be taken at the design stage. Problems arise will affect project schedule, cause delay and even bring additional workload for other engineers and also fabricator that are eventually costly and time consuming. Therefore, it is crucial that a design engineer has an appreciation and knowledge of influential considerations which affect joint strength. The design spreadsheets created were verified based on worked examples and case studies of different scenarios. From the design, it can be concluded that chord face failure most of the time governed the joint strength as the value calculated for chord face failure is lesser than that of punching shear failure in both axial and moment resistances. Recommendations on design of joint have been proven using the design spreadsheets created. Joint capacity can be increased by adopting a lower chord diameter to thickness ratio (γ), a higher brace diameter to chord diameter ratio (β), or smaller bracing angle (θ) for all the CHS joints. Gap between brace members should be kept to minimal in order to gives maximum joint capacity. Gap joints for K and N joints are preferred if compared to overlap joints due to the reason that the members are easier to prepare, fit and weld. However, overlap joints giving a higher joint capacity if compared to gap joint had been proven. Decision on type of joint will be made depending on factors such as economic and others. In conclusion, the aim of this research project has been achieved. A design tool that can be used to determine the static design capacities of uniplanar and multiplanar joints in steel hollow sections has been created using Microsoft Excel Spreadsheets. The Spreadsheets have been verified to ensure the accuracy and applicability of the design tool created.

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Future Work Recommendations Finite Element Analysis software can be used to further verify the design tool created using Microsoft Excel Spreadsheets. Another way of verifying the design tool created will be experimental studies which may be costly and time consuming. Equipments needed for experimental studies may not be available. Design tool for CHS joint connecting gusset plates to CHS members can be one of the future works recommendations. Other than that, design tool can be created for CHS joints connecting open sections such as I and H sections or Rectangular Hollow Sections (RHS) to CHS members. Also, design tool for special types of welded CHS joints can also be generated to design special joints as mentioned in Eurocode 3-2005. Many researches had been done on reinforced joints, composite joints and High Strength Steel in CHS joints. Reinforced joint can be those mentioned in Section 2.3.2. Reinforcements can be done using collar plate, doubler plater and also grouted chord. CHS joints using High Strength Steel can be applied in steel construction for civil engineering when both weight and space occupied are critical. These could be recommendations that can be done in the future.

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REFERENCES

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6.0 REFERENCES Blodgett, OW & Miller DK 1999, Welded Connections, the Lincoln Electric Company, viewed 11 March 2011, .

BSI 2005, Eurocode 3: Design of Steel Structures -- Part 1 -8: Design of Joints, British Standards Institution, United Kingdom.

Calzón, JM, Jiménez, CC, Ding, JM, Zhao, X & Sun HH 2010, ―Structural design of the Spanish Pavilion for the Expo 2010 in Shanghai‖, Tubular Structures XIII, Hong Kong , 1517 December 2010, 13th International Symposium on Tubular Structures, The University of Hong Kong, Hong Kong, pp. 365-372.

Chantal 2010, Spanish Pavilion at Shanghai Expo 2010, viewed 12 March 2011, .

Chapter One Introduction 2005, NUS, viewed 13 March 2011, .

Choo, YS, van der Vegte, GJ, Zettlemover, N, Li, BH & Liew, JYR 2005, ―Static strength of T-joints reinforced with doubler or collar plates, I: Experimental investigations‖, Journal of Structural Engineering, ASCE, 131(1): 119–128.

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Dale, K 2005, Innovative Tubular Connections, Department of Civil Engineering, Monash University, , viewed 9 March 2011, .

Design of SHS Welded Joints 2005, Corus Tubes, viewed 7 March 2011, .

Engineering

&

Training

center

2000,

TumCivil,

viewed

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March

2011,

.

Fung, TC, Chan, TK & Soh, CK 1999, ―Ultimate Capacity of Doubler Plate-Reinforced Tubular Joints‖, Journal of Structural Engineering, ASCE, 125(8):891–899.

Hollow sections for structural and mechanical application 2010, Tata Steel, viewed 5 March 2011, .

Hoon, KH, Wong, LK & Soh, AK 2001, ―Experimental Investigation Of A Doubler-Plate Reinforced Tubular T-Joint Subjected To Combined Loadings‖, Journal of Consructional Steel Research, 57(9): 1015–1039.

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Joints

in

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Hollow

Section

2011,

Tata

Steel,

viewed

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March

2011,

.

Kurobane, Y 2002, Connections in tubular structures, Wiley Online Library, viewed 12 March 2011, < http://onlinelibrary.wiley.com/doi/10.1002/pse.102/pdf>.

Lecture 13.3: The Behaviour and Design of Welded Connections between Rectangular Hollow Sections under Predominantly Static Loading n.d., UNI LJ, viewed 15 March 2011, < http://www.fgg.uni-lj.si/kmk/esdep/master/wg13/l0300.htm>.

Lee, MMK & Llewelyn-Parry, A 2004, ―Offshore Tubular T-Joints Reinforced With Internal Plain Annular Stiffeners‖, Journal of Structural Engineering, ASCE, 130(6): 942–951.

Lee, MMK & Llewelyn-Parry, A 2005, ―Strength Prediction For Ring-Stiffened DT-Joints In Offshore Jacket Structures‖, Engineering Structures, 27(3): 421–430.

Lemoine, J 2011, Advantages of Microsoft Excel, eHow, viewed 15 March 2011. .

LUSAS Bridge software - Key Features 2010, LUSAS, viewed 17 March 2011, .

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Mitri, HS, Scola, S, & Redwood, RG 1987, ―Experimental investigation into the behaviour of axially loaded tubular V-joints‖, Proceedings CSCE Centennial Conference, Montreal, Canada, pp.397-410.

Morris, C 2006, SHS Joint Design Examples, Corus Tubes, viewed 8 May 2011, < http://www.corusconstruction.com/file_source/StaticFiles/Construction/Tubes/CTSHS%20Joint%20Design%20Examples%2015-02-06.pdf>.

Oyj, R & Vainio, H 2000, Design Handbook for Rautaruukki Structural Hollow Sections, Otava Book Printing Ltd, Keuruu, Finland.

Packer, JA 2000, Tubular construction, Wiley Online Library, viewed 12 March 2011, .

Rahman, NA 2005, Static Strength of Tubular DT Joints Using Lusas Finite Element Software, UTM, viewed 9 March 2011, .

Rey, F 2007, NCCI: Design Model for Welded Joints in Trusses Using Structural Hollow Sections , Steelbiz, viewed 15 March 2011, .

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Shao, YB, Jin, YF, Zhang, JC, Qiu, ZH, Chiew, SP & Lie, ST 2010, ―Static Behaviour of Complicated Multi-Planar Tubular Joints—A Case Study In Guangdong Science Center‖, Tubular Structures XIII, Hong Kong , 15-17 December 2010, 13th International Symposium on Tubular Structures, The University of Hong Kong, Hong Kong, pp. 103-108.

Shao, YB, Zhang, JC, Qiu, ZH & Shang, JJ 2009, ―Strength Analysis of Large-Scale Multiplanar Tubular Joints with Inner-Plate Reinforcement‖, International Journal of Space Structures, 24(3): 161–177.

Strand7 Finite Element Analysis 2011, Strand7 Pty Ltd., viewed 17 March 2011, .

Structural Engineering Software – SPACEGASS 2011, SPACEGASS, viewed 12 March 2011, .

Structural

Hollow

Sections

2011,

Tata

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viewed

7

May

2011,

.

Structural

Sections

2011, The Engineering ToolBox, viewed 15 March 2011,

.

Structural

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Wardenier, J 2001, HOLLOW SECTIONS IN STRUCTURAL APPLICATIONS, CIDECT, Netherlands.

Wardenier, J, Kurobane, Y, Packer, JA, Dutta, D & Yeomans, N 2008, Design Guide For Circular Hollow Section (CHS) Joints Under Predominantly Static Loading, CIDECT Design Guide No. 1, 1st Edition, TÜV-Verlag, Köln, Germany.

Whitfield, S & Morris, M 2009, Welded Joints with Structural Hollow Sections, Corus Tubes, viewed 12 March 2011, < http://www.scribd.com/doc/45852978/Welded-Joints-WithStructural-Hollow-Section>.

Worked Examples for the Design of Steel Structures 1994, BRE, SCI, Ove Arup & Partners, viewed 07 May 2011, < http://www.scribd.com/doc/24265284/Worked-Examples-for-theDesign-of-Steel-Structures-Euro-Code>.

Zhao, XL, Wardenier, J, Packer, JA & van der Vegte, GJ, ―New IIW (2008) static design recommendations for hollow section joints‖, Tubular Structures XII, Shanghai, China, 8-10 October 2008, 12th International Symposium on Tubular Structures, Tongji University, Department of Structural Engineering, Shanghai, China, pp. 103-108.

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7.0 APPENDICES Appendix A: Verification Worked Examples and Case Studies

A

APPENDICES

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Appendix A1: Case 1 - T Joint with Axial and Moment Loading

A1 - 1

APPENDICES

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A1 - 2

APPENDICES

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Appendix A2: Case 2 - T Joint with Axial Loading

A2 - 1

APPENDICES

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Appendix A3: Case 3 - X Joint with Axial Loading

A3 - 1

APPENDICES

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Appendix A4: Case 4 - Gapped K Joint with Axial Loading

A4 - 1

APPENDICES

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A4 - 2

APPENDICES

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A4 - 3

APPENDICES

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A4 - 4

APPENDICES

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Appendix A5: Case 5 - Overlapped K Joint with Axial Loading

A5 - 1

APPENDICES

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A5 - 2

APPENDICES

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A5 - 3

APPENDICES

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A5 - 4

APPENDICES

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Appendix A6: Case 6 - Gapped N Joint with Axial Loading

A6 - 1

APPENDICES

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A6 - 2

APPENDICES

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A6 - 3

APPENDICES

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A6 - 4

APPENDICES

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A6 - 5

APPENDICES

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A6 - 6

APPENDICES

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A6 - 7

APPENDICES

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A6 - 8

APPENDICES

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A6 - 9

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Appendix B: Design Spreadsheets

B

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Appendix B1: Case 1 - T Joint with Axial and Moment Loading

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Appendix B2: Case 2 - T Joint with Axial Loading

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Appendix B3: Case 3 - X Joint with Axial Loading

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Appendix B4: Case 4 - Gapped K Joint with Axial Loading

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Appendix B5: Case 5 - Overlapped K Joint with Axial Loading

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Appendix B6: Case 6 - Gapped N Joint with Axial Loading

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Appendix B7: KT Joint

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Appendix B8: TT Joint

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Appendix B9: XX Joint

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Appendix B10: KK Joint

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