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1 Section 2.6 of the book. Other international standards for cold-formed steel structures which are in limit states format are the British Standard (Ref. 1.18), the Chinese Standard (Ref. 1.19) and the Eurocode (Ref. 1.20). 1.2 Common Section Profiles and Applications of Cold-Formed Steel Cold-formed steel structural members are normally used in the following applications: (a) Roof and wall systems of industrial, rural and commercial buildings Typical sections for use in roof and wall systems are Z(Zed) or C(Channel) sections as purlins with channel sections as bracing and shallow or deep profile sheeting spanning across the purlins. Screw fasteners are usually located through the crests for roofs and through the pans for walls. Concealed fasteners can also be used and eliminate penetrations in the roof sheeting. Typical sections and profiles are shown in Fig. 1.1, with the innovative Supazed TM Section in Fig. 1.2, and the Kliplok TM Concealed Fixed Sheeting in Fig A purlin lap at a cleat support is shown in Fig Simple Complex Simple Complex Z (Zed) sections C (Channel) sections (a) Typical Sections (b) Typical sheeting profiles for screwed connections (c) Typical sheeting profiles for concealed fasteners Fig. 1.1 Roof and wall section profiles 4

2 Fig. 1.2 Innovative SupaZed section Fig. 1.3 Kliplok TM concealed fixed sheeting Fig. 1.4 Purlin lap at cleat support 5

3 (b) Steel racks for supporting storage pallets Typical uprights are channels with or without additional rear flanges, or tubular sections. Tubular or pseudo-tubular sections such as lipped channels intermittently welded toe to toe are normally used as pallet beams. Typical sections are shown in Fig. 1.5 and a complete steel storage rack in Fig Detailed definitions are given in the Australian Standard AS 4084 (Ref. 1.21). A storage rack system under test is shown in Fig Fillet weld Single inclined brace (unlipped channel) Upright Bolt Brace inclined upwards Fillet weld Fillet weld Rear Brace inclined downwards flange (a) Plan view of uprights and bracing Rectangular hollow section Welded channel sections (b) Pallet beam sections Welded lipped angles Fig. 1.5 Storage rack sections Upright frame Shelf beam Shelf beam (semi-rigid joint) Upright Fig. 1.6 Complete storage rack system 6

4 Fig. 1.7 Storage rack system under test (c) Structural members for plane and space trusses Typical members are circular, square or rectangular hollow sections both as chords and webs usually with welded joints as shown in Fig. 1.8(a). Bolted joints can also be achieved by bolting onto splice plates welded to the tubular sections. Channel section chord members can also be used with tubular braces bolted or welded into the open sections as shown in Fig. 1.8(b). Cold-formed channel and zed sections are commonly used for the chord members of roof trusses of steel framed housing. Trusses can also be fabricated from cold-formed angles. A roof truss under test is shown in Fig Gap joint (a) Tubular truss Fillet welds all round Tubular top chord Tubular web member Tubular bottom chord (b) Channel section truss Bolted or welded connections Channel section top chord Channel or tubular web member Channel section bottom chord Fig. 1.8 Plane truss frames 7

5 Fig. 1.9 Roof truss under test (d) Frameless stressed-skin buildings Typical components are sheeting profiles with stiffened edges, used to form such small structures as garden sheds. (e) Domestic wall framing Typical members are lipped and unlipped channel sections as wall studs, top and bottom plates and noggins as shown in Fig. 1.10(a). Flat steel straps or panel bracing are normally used as bracing. Detailed definitions of member types are given in the NASH Standard (Ref. 1.22). (f) Floor bearers and joists Usually C-sections are used but hat sections as shown in Fig. 1.10(b) can be used. LiteSteel Beams (LSB) as described in (k) below can also be used as floor joists and bearers. A twostorey steel frame is shown in Fig Unlipped channel top plate Mechanical or welded connection Lipped or unlipped channel stud Stud inside top plate Section AA Self tapping screw Particle board sheeting A Noggin Mechanical or welded connection Noggin inside stud Hat section joists Deep hat section bearers or UB bearers Bottom plate Flat strip bracing Stud inside bottom plate A (a) Wall framing (b) Floor system Fig Domestic construction 8

6 Fig Two-storey steel framed house (g) Steel decking for composite construction Deep and shallow profile sheeting is used often with intermittent indentations to effect bonding between the concrete and steel in order to achieve composite action. Typical sections are shown in Fig Concrete Reinforcing mesh Decking profile Concrete Ribbed decking Intermittent indentations in profile (Embossments) Concrete Interlocking trough sections Fig Typical deck profiles for composite slabs 9

7 (h) Lighting towers Typical sections are tubular members which may be fabricated by welding. Section shapes may be circular or polygonal and are usually tapered. (i) Automotive applications All major structural members can be used but normally hat sections or box sections are used. (j) Rural grain storage silos Silo walls usually consist of shallow profile sheeting stiffened by hat or channel sections. (k) Cold-formed tubular members and hollow flange beams All circular (CHS) and rectangular (RHS) hollow sections produced in Australia are manufactured by cold-forming with an electric resistance weld (ERW) used to close the section. Another section called the Hollow Flange Beam (HFB) and LiteSteel TM Beam (LSB) are produced by cold-forming with two ERW welds used to produce tubular flanges. Typical sections are shown in Fig ERW weld Circular (CHS) Rectangular or Square (RHS and SHS) ERW weld Hollow Flange Beam (HFB) LiteSteel TM Beam (LSB) Fig Typical tubular sections 1.3 Manufacturing Processes Cold-formed members are normally manufactured by one of two processes. These are: Roll Forming Brake Pressing Roll forming consists of feeding a continuous steel strip through a series of opposing rolls to progressively deform the steel plastically to form the desired shape. Each pair of rolls produces a fixed amount of deformation in a sequence of the type shown in Fig In this example, a Z-section is formed by first developing the bends to form the lip stiffeners and then producing the bends to form the flanges. Each pair of opposing rolls is called a stage as shown in Fig. 1.15(a). In general, the more complex the cross-sectional shape, the greater the number of stages required. In the case of cold-formed rectangular hollow sections, the rolls initially form 10

8 Design of Cold-Formed Steel Structures (To Australian/New Zealand Standard AS/NZS 4600:2005) by Gregory J. Hancock BSc BE PhD DEng Bluescope Steel Professor of Steel Structures Dean Faculty of Engineering & Information Technologies University of Sydney fourth edition

9 PREFACE TO THE 4 th EDITION CONTENTS Page viii CHAPTER 1 INTRODUCTION Design Standards and Specifications for Cold-Formed Steel General History of Australian Cold-Formed Steel Structures Standards and USA Specifications New Developments in the 2005 Edition Common Section Profiles and Applications of Cold-Formed Steel Manufacturing Processes Special Problems in the Design of Cold-Formed Sections Local Buckling and Post-local Buckling of Thin Plate Elements Propensity for Twisting Distortional Buckling Cold Work of Forming Web Crippling under Bearing Connections Corrosion Protection Inelastic Reserve Capacity Fatigue Loading Combinations Limit States Design Computer Analysis References 20 CHAPTER 2 MATERIALS AND COLD WORK OF FORMING Steel Standards Typical Stress-Strain Curves Ductility Effects of Cold Work on Structural Steels Corner Properties of Cold-Formed Sections Fracture Toughness Background Measurement of Critical Stress Intensity Factors Evaluation of the Critical Stress Intensity Factors for Perforated Coupon Specimens Evaluation of the Critical Stress Intensity Factors for Triple Bolted Specimens References 36 CHAPTER 3 BUCKLING MODES OF THIN-WALLED MEMBERS IN COMPRESSION AND BENDING Introduction to the Finite Strip Method Monosymmetric Column Study Unlipped Channel Lipped Channel Lipped Channel (Fixed Ended) Purlin Section Study Channel Section Z-Section 46 iii

10 3.4 Tubular Flange Sections Hollow Flange Beam in Bending LiteSteel Beam Section in Bending References 49 CHAPTER 4 STIFFENED AND UNSTIFFENED COMPRESSION ELEMENTS Local Buckling Postbuckling of Plate Elements in Compression Effective Width Formulae for Imperfect Elements in Pure Compression Effective Width Formulae for Imperfect Elements under Stress Gradient Stiffened Elements Unstiffened Elements Effective Width Formulae for Elements with Stiffeners Edge Stiffened Elements Intermediate Stiffened Elements with One Intermediate Stiffener Edge Stiffened Elements with Intermediate Stiffeners, and Stiffened Elements with more than One Intermediate Stiffener Uniformly Compressed Edge Stiffened Elements with Intermediate Stiffeners Examples Hat Section in Bending Hat Section in Bending with Intermediate Stiffener in Compression Flange C-Section Purlin in Bending References 75 CHAPTER 5 BEAMS, PURLINS AND BRACING General Flexural-Torsional (Lateral) Buckling Elastic Buckling of Unbraced Simply Supported Beams Continuous Beams and Braced Simply Supported Beams Bending Strength Design Equations Distortional Buckling Flange Distortional Buckling Lateral-Distortional Buckling Basic Behaviour of Purlins Linear Response of Channel and Z-sections Stability Considerations Sheeting and Connection Types Design Methods for Purlins No Lateral and Torsional Restraint Provided by the Sheeting Lateral Restraint but No Torsional Restraint Lateral and Torsional Restraint Bracing Inelastic Reserve Capacity Sections with Flat Elements Cylindrical Tubular Members Examples Simply Supported C-Section Purlin Distortional Buckling Stress for C-Section Continuous Lapped Z-Section Purlin Z-Section Purlin in Bending References 122 iv

11 CHAPTER 6 WEBS General Webs in Shear Shear Buckling Shear Yielding Webs in Bending Webs in Combined Bending and Shear Web Stiffeners Web Crippling (Bearing) of Open Sections Edge Loading Alone Combined Bending and Edge Loading Webs with Holes Examples Combined Bending and Shear at the End of the Lap of a Continuous Z-Section Purlin Combined Bearing and Bending of Hat Section References 139 CHAPTER 7 COMPRESSION MEMBERS General Elastic Member Buckling Flexural, Torsional and Flexural-Torsional Buckling Distortional Buckling Section Capacity in Compression Member Capacity in Compression Flexural, Torsional and Flexural-Torsional Buckling Distortional Buckling Effect of Local Buckling Monosymmetric Sections High Strength Steel Box Sections Examples Square Hollow Section Column Unlipped Channel Column Lipped Channel Column References 164 CHAPTER 8 MEMBERS IN COMBINED AXIAL LOAD AND BENDING Combined Axial Compressive Load and Bending - General Interaction Equations for Combined Axial Compressive Load and Bending Monosymmetric Sections under Combined Axial Compressive Load and Bending Sections Bent in a Plane of Symmetry Sections Bent about an Axis of Symmetry Combined Axial Tensile Load and Bending Examples Unlipped Channel Section Beam-Column Bent in Plane of Symmetry Unlipped Channel Section Beam-Column Bent about Plane of Symmetry Lipped Channel Section Beam-Column Bent in Plane of Symmetry References 180 v

12 CHAPTER 9 CONNECTIONS Introduction to Welded Connections Fusion Welds Butt Welds Fillet Welds subject to Transverse Loading Fillet Welds subject to Longitudinal Loading Combined Longitudinal and Transverse Fillet Welds Flare Welds Arc Spot Welds (Puddle Welds) Arc Seam Welds Resistance Welds Introduction to Bolted Connections Design Formulae and Failure Modes for Bolted Connections Tearout Failure of Sheet (Type I) Bearing Failure of Sheet (Type II) Net Section Tension Failure (Type III) Shear Failure of Bolt (Type IV) Screw Fasteners and Blind Rivets Rupture Examples Welded Connection Design Example Bolted Connection Design Example References 208 CHAPTER 10 DIRECT STRENGTH METHOD Introduction Elastic Buckling Solutions Strength Design Curves Local Buckling Flange-distortional buckling Overall buckling Direct Strength Equations Examples Lipped Channel Column (Direct Strength Method) Simply Supported C-Section Beam References 218 CHAPTER 11 STEEL STORAGE RACKING Introduction Loads Methods of Structural Analysis Upright Frames - First Order Upright Frames - Second Order Beams Effects of Perforations (Slots) Section Modulus of Net Section Minimum Net Cross-Sectional Area Form Factor (Q) Member Design Rules Flexural Design Curves Column Design Curves 226 vi

13 Distortional Buckling Example References 235 SUBJECT INDEX BY SECTION 236 vii