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The paper presents an experimental program on a structural system, consisting of three long-span portal frames. The primary structural members, including columns and rafters, were constructed using cold-rolled aluminium back-to-back built-up channel sections. The system configuration featured two bays of single-span cold-rolled aluminium portal frames connected in parallel by a series of purlins spanning between the rafters to create a free-standing structure. A total of three full-scale tests (Frame Tests 1,2 & 3) were conducted with two loading scenarios. Frame Tests 1&2, which were identical to ensure accuracy, were subjected to vertical loads only, while Frame Test 3 underwent testing with combined horizontal and vertical loads. In all the tests, the columns were unbraced. The main objectives of this paper are, first, to describe the test setups and observe the structural behaviours of the portal frame systems. Consequently, the ultimate capacities were determined, and the predominant failure modes of the portal systems were identified as flexural-torsional buckling of the unbraced columns. The paper also provides information on the mechanical properties of the aluminium alloy 5052-H36 materials used to fabricate the structural members and frame components, obtained from compressive and tensile coupon tests. Further, the elastic buckling loads of the columns in the frame systems are reported in this paper, as determined from the measured load-deformation curves. While this paper primarily delves into the behaviour of the cold-rolled aluminium portal frames with a focus on flexural torsional buckling failures of unbraced columns, the authors have also conducted a separate study on the same system. In that separate study, the portal frames with the columns predominantly restrained against flexural-torsional buckling were investigated to enhance the ultimate capacities of the portal frame systems. • Three full-scale portal frames fabricated from cold-rolled aluminium back-to-back built-up channel sections are tested. • Aluminium alloy 5052-H36 materials are used to fabricate the cold-rolled aluminium structural members and frame components. • Portal frames are tested under two loading cases, including vertical loads only and combined horizontal and vertical loads. • Observed failure mode of the portal frames is flexural-torsional buckling of the unbraced columns. • Elastic critical loads of the columns of the portal frame tests are determined using the measured load-deformation curves. [ABSTRACT FROM AUTHOR]

The complex behavior of high-strength steel staggered-hole bolted connections failing in block shear with a combination of tension and inclined shear behavior was studied in this work. In particular, the location of the fracture paths in the staggered zones correlated with the angle of the staggered holes instead of appearing on the centerline between the staggered holes. Furthermore, the nominal shear strength of the staggered-hole bolted connections in the staggered paths was affected by the combination of shear and tension rupture, accounting for two components, which were the shear strength on failure paths parallel to the force and the tension strength on the segments perpendicular to the force. Consequently, a design equation for block shear strength with staggered holes was proposed to account for the combined actions. It demonstrated better correlation with the experimental results than the predictions from current design standards. A total of 88 specimens with two G450 sheets with thicknesses of 1.9 and 2.4 mm were modeled by means of a finite-element model validated against the actual tests to achieve reliable data using a parametric procedure. In addition, four different types of configurations, including not only four holes but also three and five holes were modeled to investigate the effect of the inclined shear and tension zones on the block shear strength and behavior of the connections. The large data set was used for the verification procedure of the proposed formula. [ABSTRACT FROM AUTHOR]

This study proposes an innovative type of simple connection utilizing power-actuated fasteners to join a cold-formed steel channel to a rectangular hollow section column via a web-side plate or a T-section. An experimental program composed of 26 specimens was carried out to investigate the behavior of the connections under the combination of shear and rotation. The experimental results are discussed in two limit states including bearing and pull-out by shear. An analytical model is proposed to predict the shear strength of the connections based on the provided information of vectorial force at a fastener, displacement, and rotation at the connections. The proposed model yields a conservative prediction for the tested connections with a mean test-to-prediction ratio of 1.05 and the coefficient of variation of 6% or 9%, depending on the limit state. A design example is provided to illustrate the implementation of the proposed model in practice. [ABSTRACT FROM AUTHOR]

• Experiments on the member buckling and ultimate strengths of cold-rolled aluminium alloy channel columns are performed. • The aluminium alloy 5052-H36 materials are used to fabricate the cold-rolled aluminium structural channel columns. • Non-linear FE models are developed using ABAQUS to simulate laboratory experiments and calibrated against the test results. • A parametric study based on FE models is performed to extend the data by varying cross-section dimensions and member lengths. • Experimental and numerical results are ued to calibrate the new design equations for cold-rolled aluminium alloy columns. The paper first presents the development of detailed finite element (FE) models for investigating the member capacity of cold-rolled aluminium alloy 5052-36 channel columns. The numerical non-linear FE models are developed using the commercial FE software package ABAQUS to simulate laboratory experiments and calibrated against the test results. The experimental program was performed by the authors at the University of Sydney and the detailed test results are fully described in a companion paper. The calibrated numerical FE models with actual mechanical properties and measured geometric imperfections in analyses accurately predict the experimental results and behaviours, including flexural and flexural-torsional buckling as well as local-global interaction buckling failure modes. A parametric study is subsequently performed to extend the data range by varying cross-section dimensions and member lengths. The effects of loading eccentricity positions and initial geometric imperfections are also considered in the parametric study. The experimental and numerical results are compared with design strength predictions from current Australian/New Zealand, American and European specifications for aluminium structures in the companion paper. In this paper, the Direct Strength Method (DSM) for the design of compression members as per the Australian/New Zealand standard AS/NZS 4600 for cold-formed steel structures is adopted for comparison. The DSM design rules for cold-formed steel compression members are found to provide more accurate predictions than those of current specifications for aluminium structures and therefore used to propose improved design equations for cold-rolled aluminium alloy columns. Finally, a reliability analysis is performed to evaluate the safety level of current design specifications and the proposed design rules. [ABSTRACT FROM AUTHOR]

• A series of compression tests to investigate member buckling behaviour and ultimate strengths of cold-rolled aluminium alloy channel columns are performed. • The aluminium alloy 5052-H36 materials are used to fabricate the cold-rolled aluminium structural channel columns. • The observed failure modes are flexural, flexural-torsional and local-global interaction buckling failure modes. • The experimental results are compared with predictions by current Australian/New Zealand, North American and European design specifications. Cold-rolled aluminium alloy sections have been recently introduced in Australia as newly developed thin-walled products. To fabricate these sections, the roll-forming process used in cold-formed steel production has been employed, which has proven to be more cost-effective than the conventional extrusion process. This paper describes a series of compression tests to investigate member buckling behaviour and ultimate strengths of cold-rolled aluminium alloy 5052-36 channel columns. Twenty-eight specimens of three commercially available sections (C10030, C25025 and C40030) were tested at the University of Sydney. Two configurations of end boundary conditions were specially designed to capture flexural, flexural-torsional and local-global interaction buckling failure modes. Prior to testing, initial geometric imperfections were measured using a laser scanning method, and flat/corner coupons were tested to determine compressive and tensile strengths of the aluminium alloy material. The experimental results are compared with ultimate column strength predictions by current Australian/New Zealand, North American and European design specifications for aluminium structures. Additionally, the test results provide data for calibration of finite element models of cold-rolled aluminium structural members for use in parametric and similar studies. A companion paper describes such parametric study and the derivation of new design guidelines for member buckling of cold-rolled aluminium channel columns based on the numerical parametric data and the experimental data presented herein. [ABSTRACT FROM AUTHOR]

Two test series were carried out on angle cleat connections between cold-formed channels as beams and rectangular hollow sections as support members. The objective of the tests was to determine the effect of connection rotation from the beam on the shear capacity of the connection. Self-drilling screws were used to attach the channels to the angle cleats with the failure limit states always occurring in this part of the connection. A dual actuator test apparatus that could apply controlled displacement and rotation to the beams was used. The specimens contained different thicknesses of the channels, which allowed for two limit states involving failure modes of the screws fracturing in shear and bearing as well as tilting failure of the screws in the channel sheet material. The experimental results show the effect of rotation on reducing the shear capacity of the screwed connections. An analytical model for the connection is developed using the relation between the bearing force and deformation of the individual screw connections. [ABSTRACT FROM AUTHOR]

A total of 105 cross-tension tests were conducted to investigate the strength and behavior of power-actuated fastener (PAF) connections under quasi-static monotonic tensile loading. Three types of PAF were used to join sheets with thicknesses ranging from 0.75 to 4.00 mm to thicker plates with thicknesses ranging from 3.00 to 20.0 mm. All of the steel materials were high-strength cold-formed steel, except for the 20-mm-thick steel, which was hot-rolled steel. The studied parameters were the type and diameter of the fasteners and the thicknesses of the top and base steel materials. The majority of the specimens failed by pull-out failure, although some thinner sheets failed by transverse fracture of the top sheet. The test results reveal that PAF connections exhibit a high tensile capacity as long as a sufficient embedment length is provided. A model is proposed to evaluate the pull-out strength of PAF connections based on the base material strength and the average embedded diameter and embedment length of the fastener. The proposed model produces a mean of test-to-prediction ratio equal to 1.02 with a coefficient of variation ranging from 0.12 to 0.16. Reliability analyses were carried out and resulted in a resistance factor of 0.56–0.69 for Load and Resistance Factor Design. [ABSTRACT FROM AUTHOR]

This paper presents an application of the Digital Image Correlation (DIC) based technique to investigate the block shear failure mode of bolted connections made of high strength cold-reduced G450 sheet steel. In conjunction with the conventional testing approach, the DIC provides detailed failure information on connection behaviour and its correlation with macroscopic material tests. A total number of 12 tests of 3 mm thickness specimens were tested at the University of Sydney. The experimental results provide a better understanding on how the failure of the bolted connections progress. The features of the new block shear equations recently adopted in the North American Specification for Design of Cold-Formed Steel Structural Members (AISI S100:2016) and the Australian/New Zealand Standards 4600:2018 Cold-Formed Steel Structures have been clarified. • A block shear failure experimental program of bolted connections using high strength G450 sheet steel is performed. • The Digital Image Correlation (DIC) is used to observe the failure of the bolted connections. • Test results are compared with the predictions in AISI S100:2016 and AS/NZS 4600:2018. • The average shear area used in the block shear equation in the latest AISI S100:2016 and AS/NZS 4600:2018 has been confirmed. [ABSTRACT FROM AUTHOR]

Shear behaviour of cold-formed steel beams with an aspect ratio (shear-span/web-depth) of 1.0 has been studied thoroughly, mainly using central point load tests. However, for beams with higher aspect ratios, the effect of bending causes a reduction of shear capacity and alters the failure modes. This paper introduces a new test setup, the dual actuator test rig, which is equipped with two actuators moving independently at customizable displacement rates to control and minimize applied bending moments in the shear spans of interest. Shear strength close to pure shear capacity can be therefore reached even at an aspect ratio of 2.0. Experimental series recently performed at the University of Sydney on channel section members using the new test configuration is presented. The experimental results together with other available experimental data are combined and used to validate and re-calibrate the Direct Strength Method design formulae incorporated in the AISI S100:2016 Specification and the AS/NZS 4600:2018 Standard. • An experimental program of cold-formed channel sections in shear with aspect ratio of 2.0 is performed • A new dual actuator test rig for testing channel sections in shear with minimum bending effect is developed and conducted • Test results affirmed the applicability of the DSM shear design provisions with shear span aspect ratios up to 2.0 • All test results on CFS channels with aspect ratios of 1.0 and 2.0 are used to recalibrate the DSM shear design rules • Resistance factors of 0.95 (AISI S100-16) and 0.9 (AS/NZS 4600:2018) for the DSM shear strength predictions are confirmed [ABSTRACT FROM AUTHOR]

Shear behaviour of cold-formed steel beams with an aspect ratio (shear span/web depth) of 1.0 has been studied thoroughly, mainly using central point load tests. However, for beams with longer aspect ratios, the effect of bending causes reduction of shear capacity and alters the failure modes. This paper summarises experiments recently performed at the University of Sydney on channel section members using a new test configuration to minimize bending moments. Shear strength close to pure shear capacity can be therefore reached even at an aspect ratio of 2.0 . The test results were compared with the strength predictions using the current direct strength method (DSM) of design for shear specified in the North American specification for the design of cold-formed steel structural members, AISI S100:2016 and the Australian/New Zealand Standard for cold-formed steel structures, AS/NZS 4600:2018. A good agreement between the experimental results and the predicted values has confirmed the viability of the DSM design rules for structures with aspect ratios up to 2.0 . Numerical models were developed to foresee potential issues prior to the experimental work, and were subsequently calibrated against the tests to produce reliable results. [ABSTRACT FROM AUTHOR]

In the literature, the block shear and tear-out phenomena and strengths of cold-formed steel bolted connections have been well understood and thoroughly investigated. However, the strength of these failure modes in the bolted connections between thin and thick plates may be governed by the effect of out of plane curling of the thin plate, and this phenomenon has not been studied in detail yet. It is apparent that the curling not only affects the shear strength but also changes the behaviour of the bolted connections. In particular, the design shear strength of the bolted connections remains unchanged with high ductility even though the end distance between the bolt holes and the free edge is becoming larger. An experimental program on the block shear and tear-out behaviour of bolted connections was performed at the University of Sydney in order to provide a better understanding on the effect of the curling. A total of 48 tests including thicknesses of thin plates (1.0 mm, 1.2 mm and 1.9 mm) and 10 mm thick plates was conducted at the University of Sydney with three configurations of bolted connections in conjunction with two different hole diameters (9 mm and 14 mm) and various end distances as the main variables. Three different failure modes being block shear, tear-out and curling were observed in the tests. In addition, different material properties of the cold-formed sheet steels (i.e., G300, G450, G500 and G550) were also considered in this program to create a large database for the investigation. Consequently, a design equation for block shear and tear-out strength accounting for the curling effect is proposed in this paper. It provides a better correlation with the experimental results than those predicted in the current Australian and New Zealand Standard (AS/NZS 4600) and the North American Specification for cold-formed steel structures (AISI S100). In addition, a calibrated Finite Element Model (FEM) was subsequently developed using the commercial finite element program ABAQUS to verify against the test results. The reliable data set of the FEM models is further utilised to extend the data range in a parametric study and is finally used for the verification procedure of the proposed formula over a wider range of data. • An experimental program on the block shear and tear-out behaviour of bolted connections is performed • Effect of curling phenomenon on the shear strength and the behaviour of the bolted connections is investigated • Finite Element Method (FEM) models are developed using the commercial FEM program ABAQUS to verify against the test results • Reliable FEM data set is used for extending the data range and for the verification procedure of the proposed formula • A design equation for block shear and tear-out strengths accounting for the curling effect is proposed [ABSTRACT FROM AUTHOR]

The recently incorporated Direct Strength Method (DSM) rules for shear in the North American Specification for Cold-Formed Steel Structural Members (NAS S100:2012) consist of design equations for unperforated sections with and without Tension Field Action (TFA). The TFA is mobilised as a result of the development of diagonal tension due to the full depth bolt restraints. The design shear equations based on a reduction factor α to account for reduced TFA were proposed by Pham and Hancock in cases of partly bolted connections with lateral flange restraints. This paper presents an experimental program to further investigate the TFA of cold-formed C-sections in shear. A total of twelve tests were carried out at the University of Sydney. Three different bolted connection configurations were chosen with and without lateral restraints of the top flanges at the supports. Numerical simulations using the Finite Element Method (FEM) were also performed to validate test results and extend data range. For tests without lateral flange restraints, combined twisting and shear failure modes were observed. The lack of lateral flange restraint leads to a significant reduction of the ultimate load especially when more bolts were removed. Based on these experimental and FEM modelling data, a further reduction factor β dependent upon the slenderness of the sections is introduced in this paper to account for the lack of lateral flange restraint along with the previously proposed reduction factor α which accounts for bolt reduction. [ABSTRACT FROM AUTHOR]

Thin-walled structural channel members are commonly manufactured with cut-outs to allow access for building services such as plumbing, electrical and heating systems in the walls and ceilings. The presence of holes in the members will cause changes in the stress distribution and there will be consequently changes in the buckling characteristic and ultimate strength capacity. Recent work by Pham and Hancock has provided solutions to determine the shear buckling load using the Spline Finite Strip Method (SFSM) for whole thin-walled channel sections without holes. In this paper, the same methodology is utilised to study and provide solutions to the elastic shear buckling firstly for the perforated square plates and subsequently for the whole thin-walled lipped channel sections with centrally located holes. Both circular and square holes with the same sizes and diameters were chosen for investigation. The main variables are the diameters of the circular holes and the sizes of the square holes. While there is only uniform pure shear applied throughout in square plates, three different cases for shear loading in the channel are considered to maintain longitudinal equilibrium. The method is also benchmarked against the Finite Element Method (FEM) using software package ABAQUS/Standard in all cases. Comparisons between hole shapes, loading cases and buckling modes of both square plates and channels are included. For design purposes, approximate equations for shear buckling coefficients of square plate and channel section containing central circular and square holes are also proposed in this paper. Design example is also provided for design purposes. [ABSTRACT FROM AUTHOR]

The paper presents the development of new design guidelines for cold-rolled aluminium alloy 5052-H36 channel beams subject to global buckling. The validation data are obtained from the experimental and numerical Finite Element (FE) results as performed in previous studies by the authors. The failure modes in the experiments were observed as flexural–torsional buckling modes, and good agreement was achieved between the experimental and FE results. Based on the reliable and calibrated FE models, a parametric study is carried out in this paper to extend the data range by varying section dimensions and member lengths. Subsequently, all experimental and FE ultimate strengths of the parametric study are compared with nominal member capacities of aluminium beams as predicted by the current Australian/New Zealand, American and European aluminium design standards. Additionally, the Direct Strength Method (DSM) design rules from the Australian and New Zealand standard - AS/NZS 4600 for cold-formed steel structures are applied to predict member bending capacities for comparisons. Finally, reliability analyses are performed to evaluate the efficiency of the abovementioned design methods. It is found that the design guidelines for nominal member bending capacities to the AS/NZS 4600 standard provide accurate predictions and are therefore proposed to be used for the design of cold-rolled aluminium alloy channel beams as investigated in this paper. • New design guidelines for cold-rolled aluminium alloy H36-5052 channel beams subject to global buckling are developed. • The 5000-series high magnesium alloy, 5052-H36, is used for fabricating cold-rolled aluminium channels. • Detailed finite element (FE) models using the software ABAQUS are developed for a parametric study. • Experimental and FE ultimate strengths are compared with nominal member capacities of aluminium beams in the current aluminium design codes. • Design rules for member bending capacities to the AS/NZS 4600 standard are proposed for design of cold-rolled aluminium channel beams. [ABSTRACT FROM AUTHOR]

For flexural thin-walled section beams, the ultimate strength is significantly affected by the interaction of different local buckling modes associated with combined bending and shear stresses. This paper provides a comprehensive analytical and numerical study of elastic buckling of thin-walled channels subjected to different combinations of bending and shear stresses. The commercial ABAQUS software package using Finite Element Method (FEM) has been used to perform the elastic buckling analyses of the channel sections. The results are benchmarked against those from the Semi-Analytical Finite Strip Method (SAFSM) for the cases of pure bending and shear only. Two typical types of channels with and without lips are selected for investigation. To study the effect of different combinations of bending and shear on the buckling stresses, different normal stress distributions and equilibrating shear stresses are applied at two end cross-sections of the channels to maintain static equilibrium. Different types of interactions which occur during the buckling analyses are studied by varying the ratios of bending moments resulting from the modelled longitudinal stresses. A new concept for the elastic local buckling interaction based on the Average Bending Moment (ABM) at buckling is provided. In addition, an explicit approach for local buckling loads of channels under different combinations of bending and shear is also introduced for the practical design use. The results from this explicit solution for elastic buckling can be used as direct inputs for an explicit Direct Strength Method (DSM) design of members under combined bending and shear. • A comprehensive study of elastic buckling of thin-walled channels under combined bending and shear stresses is performed • ABAQUS software package using FEM is used to conduct elastic buckling analyses of thin-walled channel sections • Results are benchmarked against those from the Semi-Analytical Finite Strip Method for the cases of pure bending and shear only cases • A new concept for elastic local buckling interaction based on the Average Bending Moment (ABM) at buckling is provided • Results from the explicit solution for elastic buckling analyses can be used in the Direct Strength Method (DSM) of design [ABSTRACT FROM AUTHOR]

In practice, there is a wide variety of commercially available channel sections with complex shapes where the web is stiffened by adding longitudinal intermediate stiffeners. These stiffeners may improve the shear capacity of the channels. Recently, the Direct Strength Method (DSM) of design of cold-formed sections has been extended in the North American Specification for Cold-Formed Steel Structural Members (NAS S100:2012) to include shear based on research by the authors. The prequalified sections include flat webs and webs with small intermediate longitudinal stiffeners. To extend the range to larger intermediate stiffeners as occurs in practice, a series of predominantly shear tests of lipped channel sections with one web stiffener of different shapes and various sizes has been performed at the University of Sydney. Six different types of stiffened web channel sections were tested along with an additional reference plain section. All tests were conducted with straps screwed on the top flanges adjacent to the loading points. These straps provide torsion/distortion restraints which may enhance the shear capacities of the sections. The test failures were observed mainly in the combined bending and shear modes. Numerical simulations based on the Finite Element Method (FEM) using the software package ABAQUS/Standard are also performed to compare with and calibrate against the tests. The accurate results from the FEM models allow extension of the test data. Based on the reliable FEM models, a series of FEM modelling of predominantly shear tests for stiffened web channels has been performed without straps attached to the top flanges adjacent to loading points. The test and FEM results are subsequently plotted against the DSM interaction curves between bending and shear where the interaction is found to be significant. An extended range of DSM prequalified sections with longitudinally stiffened web channels in shear is proposed in this paper. [ABSTRACT FROM AUTHOR]

Thin-walled sections under localised loading may lead to web crippling of the sections. This paper develops the Semi-Analytical Finite Strip Method (SAFSM) for thin-walled sections subject to localised loading to investigate web crippling phenomena. The method is benchmarked against analytical solutions, Finite Element Method (FEM) solutions, as well as Spline Finite Strip Method (SFSM) solutions. The paper summarises the SAFSM theory then applies it to the buckling of plates, and channel sections under localised loading. Multiple series terms in the longitudinal direction are used to compute the pre-buckling stresses in the plates and sections, and to perform the buckling analyses using these stresses. Solution convergence with increasing numbers of series terms is provided in the paper. The more localised the loading and buckling mode, the more series terms are required for accurate solutions. The loading cases of Interior One Flange (IOF) and Interior Two Flange (ITF) are investigated in this paper using simply supported boundary conditions. [ABSTRACT FROM AUTHOR]

Abstract: The plain Z-section is one of the most common cold-formed steel purlins in use for roof systems. Its lapping ability provides continuity, and double thickness material at the support regions results in greater performance and more economical designs. Design methods for this section are normally specified in the Australian/New Zealand Standard for Cold-Formed Steel Structures or the North American Specification for Cold-Formed Steel Structural Members. The newly developed Direct Strength Method (DSM) presented (Chapter 7 of AS/NZS 4600:2005, Appendix 1 of NAS S100-2007) is limited to pure compression and pure bending. Recently, design proposals for shear, and combined bending and shear for DSM have been added to the 2012 Edition of the North American Specification. The situation of combined bending and shear as occurs in a continuous purlin system is not considered in detail. Hence, this paper presents numerical simulations using the Finite Element Method (FEM) to determine the ultimate strength. The simulations are compared with and calibrated against tests at two lap lengths. For each lap length, tests were also conducted with and without straps screwed on top flanges. These straps provide torsion/distortion restraints which may enhance the capacity of the purlins. The accurate results from FEM allowed extension of test data by varying the lap lengths and section thicknesses. The results of both the experimental tests and FEM were used and plotted on the recently proposed DSM design interaction curves. Proposals for an extension to the DSM in combined bending and shear are given in the paper. [Copyright &y& Elsevier]

Abstract: The finite strip method employs simple polynomial functions to describe the transverse variations of the displacements and continuous harmonic series functions or discontinuous spline functions to describe the longitudinal variation of the strip displacements. While the Semi-Analytical Finite Strip Method (SAFSM) generally uses the longitudinal harmonic series to satisfy the boundary conditions at the longitudinal ends and to give compatibility between strips, the Spline Finite Strip Method (SFSM) employs local spline functions in the longitudinal direction to account for different boundary conditions. The Semi-Analytical Finite Strip Method (SAFSM) has been widely used in computer software (THIN-WALL, CUFSM) to develop the signature curves of the buckling stress versus buckling half-wavelength for a thin-walled section under compression or bending to allow identification of buckling modes. Recently, a complex mathematical technique has been applied in the SAFSM theory to allow for the case of shear. This paper provides the analysis and comparison between the new SAFSM development for shear and the SFSM for whole plain channel sections including flanges and lips where the sections are loaded in pure shear parallel to the web. The main variables are the flange widths and lip sizes. The SAFSM is limited to a single half-wavelength whereas the SFSM can include multiple buckles as seen in the well-known garland curve. The paper demonstrates the potential for coupling between multiple short half-wavelength modes in shear and longer single half-wavelength as may occur in distortional buckling. [Copyright &y& Elsevier]

Plain C- or Z-sections are two of the most common cold-formed steel shapes in use throughout the world. Other shapes are high-strength SupaCee and SupaZed (Bluescope Steel Ltd., Melbourne, Australia) steel sections, which are widely used in Australia as purlins in roof and wall systems. They contain additional return lips and web stiffeners that enhance the bending capacity of the sections. Design methods for these sections are normally specified in the Australian/New Zealand Standard for cold-formed steel structures or the North American Specification for cold-formed steel structural members. In both standards, which include the newly developed direct strength method of design (DSM), the method presented is developed for beams and columns, including the reliability of the method. This paper presents two different test series on both plain C- and SupaCee sections in pure bending (constant moment). They were performed at the University of Sydney for the extension of the DSM to include channel section beams with complex stiffeners. Two different section depths and three different thicknesses of high-strength lipped channel sections were tested in pure bending. Tests with and without torsion/distortion restraint straps screwed on the top flanges in the pure bending region were also considered to allow local and distortional buckling to form in the sections, respectively. Test results and formulas developed from the DSM are summarized in the paper. Three different cases where moments are used in association with yield, inelastic, or plastic criteria in the DSM local and distortional strength equations are compared with the test data. By comparisons between cases, a proposed recommendation for DSM inelastic buckling strength design in pure bending with extended nondimensional slenderness limit for both local and distortional buckling is given in the paper. [ABSTRACT FROM AUTHOR]

Abstract: Buckling of thin-walled sections in pure shear has been recently investigated using the Semi-Analytical Finite Strip Method (SAFSM) to develop the “signature curve” for sections in shear. The method assumes that the buckle is part of an infinitely long section unrestrained against distortion at its ends. For sections restrained at finite lengths by transverse stiffeners or other similar constraints, the Spline Finite Strip Method (SFSM) has been used to determine the elastic buckling loads in pure shear. These loads are higher than those from the SAFSM due to the constraints. The SFSM requires considerable computation to achieve the buckling loads due to the large numbers of degrees of freedom of the system. In the 1980s, Anderson and Williams developed a shear buckling analysis for sections in shear where the ends are simply supported based on the exact finite strip method. The current paper further develops the SAFSM buckling theory of Y.K. Cheung for sections in pure shear accounting for simply supported ends using the methodology of Anderson and Williams. The theory is applied to the buckling of plates of increasing length and channel sections in pure shear also for increasing length. The method requires increasing numbers of series terms as the sections become longer. Convergence studies with strip subdivision and number of series terms is provided in the paper. [Copyright &y& Elsevier]

Thin-wall structural sections and members are susceptible to three fundamental instabilities: local, distortional and lateral-torsional buckling. For cold-formed purlins or girts commonly used in roof and wall systems, distortional buckling may govern the predominant failure mode when the compression flange is not attached to sheathing or panels. The paper presents an experimental and numerical investigation on the behaviour and strength of cold-rolled aluminium beams subjected to distortional buckling. A total of eighteen specimens were tested in a four-point bending configuration with six various types of cross-sections and two different thicknesses. In the pure bending region between the two loading points, the upper compression flanges were kept free to allow distortional buckling to form. Subsequently, detailed finite element (FE) models of cold-rolled aluminium beams using the software ABAQUS were developed with the incorporation of measured material inelasticity and initial geometric imperfections. Good agreement between the experimental results and the FE models was achieved. The reliable and verified FE models along with the test data in this paper will be used in a separate publication to undertake a detailed parametric study and calibration of new proposed design rules for cold-rolled aluminium beams subjected to distortional buckling. [Display omitted] • An experimental program of cold-rolled aluminium channel beams subject to distortional buckling is performed. • The 5000-series high magnesium alloy, 5052-H36, is used for fabricating cold-rolled aluminium channels. • The experimental behaviour and distortional buckling strengths of cold-rolled aluminium channel beams are presented. • Detailed finite element (FE) models using the software ABAQUS of cold-rolled aluminium beams are developed. • Good agreement between the experimental results and the FE models is achieved and will be used for a parametric study. [ABSTRACT FROM AUTHOR]

Abstract: The paper studies and provides solutions to the elastic buckling of whole channel sections including flanges and lips where the sections are loaded in pure shear parallel with the web. The elastic buckling analyses of thin-walled channel sections in pure shear have been implemented by means of the Spline Finite Strip Method (SFSM) to determine the elastic buckling loads (V cr ) of the sections. The shear buckling coefficients (k v ) of the web for design of a section are back-calculated from the shear buckling loads. The main variables are the flange widths, member lengths and lip sizes. The boundary conditions at two end sections are simply supported. The results of the analyses plotted in the format of interaction charts are given as design guidelines for designers to predict the elastic buckling shear coefficient (k v ) without using the Spline Finite Strip Method (SFSM) software. Typical buckling modes at different flange widths, member lengths and lip sizes are also included in this paper. The modes include local web and flange buckling, section distortional buckling and section twisting. [Copyright &y& Elsevier]

The direct strength method (DSM) recently included in the North American Specification and Australian/New Zealand Standard AS/NZS 4600:2005 gives design rules for compression and bending. No rules are presented in this standard for shear or for combined bending and shear. Two series of tests on C-section can be used to develop and calibrate rules for design in shear and for combined bending and shear. These are the University of Missouri Rolla tests of the 1970s and recent tests on high-strength C-sections at the University of Sydney. Both series of tests use a similar test rig, although different levels of tension field action have been observed. Two features researched are the effect of full-section shear buckling (as opposed to web-only shear buckling), and tension field action. Full-section buckling is a feature of the DSM but requires software that can evaluate full sections for shear. The paper proposes DSM design rules for C-sections in shear and for combined bending and shear both with and without tension field action. The test results are compared with the proposed design rules. [ABSTRACT FROM AUTHOR]

Abstract: For shear, the design of sections for strength is usually governed by the web plate subjected to shear force and undergoing shear buckling, or yielding in shear or a combination of the two. For webs with relatively high depth-to-thickness ratios, the shear stress distribution in the web after buckling changes and significant post-buckling strength may occur as a result of the development of a diagonal tension which is called “Tension Field Action” (TFA). Recently, the full set of shear test results for the plain lipped C- and SupaCee® sections performed at the University of Sydney shows that the post-buckling strength was attributed to TFA which was provided by the increased transverse restraints created by bolted connections attached to loading stiffeners over the full depth of the web panel at the supports and loading point. This improved the post-buckling strengths of the web in shear. Firstly, the results of finite element nonlinear simulations are compared with tests where bolted connections not over the full depth of the web panel were used to validate the FE method. Then the range of test data described previously is extended using finite element models, by reducing the bolting at support and loading points in the test data to provide further guidance on the availability of TFA in particular. Design equations are provided for Tension Field Action. [Copyright &y& Elsevier]

Abstract: The paper provides numerical nonlinear simulations, based on the finite element method (FEM) using the software package ABAQUS/Standard, of high strength C-section cold-formed steel purlins in shear and combined bending and shear. The simulations are compared with and calibrated against tests performed at the University of Sydney on a variety of section sizes and thicknesses. Studies of the effects of boundary condition, geometric imperfection, and element type as well as mesh size are included. Geometric imperfections are often taken as a scaled multiple of the eigenvalue modes. The selection of eigenmodes and their scaling is given in the paper. The accurate results of the numerical simulations show that finite element analysis can be used to predict the ultimate loads of thin-walled members including the post-buckling behavior of thin-walled sections in shear and combined bending and shear. It is demonstrated that finite element analysis can therefore be used to design and optimize thin-walled sections of high strength steel. [Copyright &y& Elsevier]

In roof systems, a high strength steel profiled sheeting fastened to high strength steel cold-formed purlins of a lipped C- or Z-section is commonly used throughout the world. The design of such systems is performed according to the provisions of the limit states Australia/New Zealand Standard for Cold-Formed Steel Structures in Australia and the North American Specification for the Design of Cold-Formed Steel Structural Members in the United States. In both standards, which include the newly developed direct strength method of design (DSM), the method presented is limited to pure compression and pure bending. The situations of pure shear and combined bending and shear as occurs in a continuous purlin system are not considered. In order to extend the DSM to purlin systems, three different test series on high strength cold-formed C-section purlins have been performed at the University of Sydney. The test series include predominantly shear, combined bending and shear, and bending only test series. Two different section depths and three different thicknesses of the lipped channel section were tested in this study. Further, tests with and without torsion/distortion restraint straps screwed on the top flanges adjacent to the loading points were also considered. This paper summarizes the test results and formulas developed from the effective width method and the DSM. Proposals for design are included in this paper. Comparisons with the Australian Steel Structures Standard are also included to take account of the tension field action. [ABSTRACT FROM AUTHOR]

The Limit States Australian/New Zealand Standard AS/NZS 4600:2005 and the North American Specification (NAS) for the Design of Cold-Formed Steel Structural Members 2001 (2004 Supplement) include the newly developed direct strength method of design (DSM). In both standards, the method presented (Chapter 7 of AS/NZS 4600:2005, Appendix 1 of NAS) is limited to pure compression and pure bending. The situation of combined bending and shear as occurs in a continuous purlin system is not considered. In order to extend the DSM to purlin systems, it is necessary to prescribe and calibrate a method for combined bending and shear. Eight different test series on purlin sheeting systems with single, double, and triple spans and both uplift and downwards load cases as well as screw and concealed sheeting have been performed at the University of Sydney over a 10-year period. As many of these tests consisted of continuous lapped purlins where combined bending and shear occurred at the purlin section just outside the end of the lap, it is possible to use these test data to propose an extension to the DSM. Furthermore, calibration of the proposals using the limit states design methodology is included in the paper. This paper makes two proposals for combined bending and shear, and calibrates them both for the full sets of vacuum rig test data. [ABSTRACT FROM AUTHOR]

This paper explores the use of the finite element software package ABAQUS/Explicit to simulate the behaviour and strength of power-actuated fastener (PAF) connections joining cold-formed steel sheet to hot-rolled steel plate subjected to monotonic shear loading. The finite element (FE) models are developed for the simulation of the entire process including both installation and loading stages. The fastener is firstly driven into the steel materials to consider the initial plastic deformations around the contacts between steel plates and fastener caused by dynamic impact. Subsequently, monotonic shear loading is applied to the PAF connections until failure by a displacement control at a low speed. Various aspects of the FE models such as fracture model of the materials, loading rate, mesh sensitivity are calibrated to optimise the computing time and improve the accuracy of the FE models. The simulations are validated against experiments conducted in a separate study by the authors, and good agreement between the test and numerical results is achieved. The accurate and reliable FE models in this study are able to simulate and provide insights into the shear behaviour of the power-actuated fastener connections in terms of initial stiffness, maximum shear capacity, failure modes as observed in the experiments (i.e., bearing, shear fracture, and pull-out of the fastener), ductility, and damage patterns of the connectors. It is demonstrated that FE analysis can therefore be used to extend experimental data in a parametric study and to optimise the design of PAF connections in shear. [Display omitted] • A FE study into shear behaviour of Power-Actuated Fastener connections is conducted. • ABAQUS/Explicit is used to simulate the installation and load application stages. • Three limit states are simulated: pull-out, shear fracture and bearing failures. • The accuracy and robustness of the FE model are validated and optimised. [ABSTRACT FROM AUTHOR]

High strength cold-formed steel channel beams widely used in roof and floor systems carrying steel profiled roof sheeting or floor decking are commonly subjected to a combined action of bending and shear in practice. The design guidelines of such purlins or beams have recently been standardised utilising shear-bending interaction curves in current standards/specifications such as the Australian/New Zealand Standard (AS/NZS 4600:2018) and the North American Specification (NAS S100–2016). In order to investigate different combinations of bending and shear, an experimental program comprising thirty tests of pure bending, combined bending and shear and predominantly shear has been performed at the University of Sydney using a dual actuator test rig. All the tests are conducted on commercial plain C-lipped and Supa-Cee channels. The interaction between bending and shear is governed by varying ratios of bending moments at two ends of the test span. All testing results are plotted against the current interaction curve to validate the performance of the current design method on channel members under different combinations of bending and shear. Further, a completely new concept for the interaction between bending and shear on a theoretical basis of statics is introduced and a development of an explicit Direct Strength Method (DSM) design for the prediction of ultimate strengths of members under combined bending and shear is also provided in this study. [Display omitted] • An experimental program on high strength cold-formed steel channel beams is performed using a dual actuator test rig. • Test configurations include pure bending, combined bending and shear, and predominantly shear. • Interaction between bending and shear is governed by varying ratios of bending moments at two ends of the test span. • A completely new concept for the interaction between bending and shear on a theoretical basis of statics is introduced. • A development of an explicit DSM design for the predictions of members under combined bending and shear is provided. [ABSTRACT FROM AUTHOR]

Cold-formed steel members are manufactured from cold-reduced steel coils by either press-braking or cold-forming. During manufacturing processes at ambient temperature, two stages, namely cold-reducing and cold-forming, create significantly large deformation on the cross-sections. While the first stage involves cold-reducing hot-rolled steel coils to thinner desired thicknesses resulting in higher yield strength and less ductility, the second stage including rolling and bending processes causes strain hardening of the material, which affects the local mechanical properties especially at the bending corners of the cross-sections. This paper presents an experimental study on the effect of the latter manufacturing process on the microstructure of flat and corner regions of C-shaped cold-formed high strength G450 steel channel sections with different sizes and thicknesses. Optical microscopy, scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) were used for microstructure analyses. Tensile coupon and Vikers hardness tests were performed for mechanical properties of cold-formed steel material including yield strength, ultimate strength and Vickers hardness at both flat and corner regions. Understanding the relationship between the changes in the microstructure of the high strength G450 steel material provides insights into the mechanical and structural behaviour of cold-formed channel members. In addition, the experimental yield strengths at corner regions are compared with those from the AISI S100-16 and AS/NZS 4600:2018 design specification/standard, showing conservative predictions of the design codes over the measured corner yield strengths, and especially providing inconsistent predictions in thin sections. Hence, a new suggested modification of design equations in the current specification/standard is proposed in this paper to better predict the yield strengths at corner regions of high strength G450 steel cold-formed channels. • Effect of manufacturing process on microstructures/mechanical properties is studied. • Flat and corner regions of cold-formed G450 steel channel sections are investigated. • Optical, scanning electron microscopy and electron backscatter diffraction are used. • Tensile coupon and Vickers hardness tests are conducted for mechanical properties. • New suggested design equations are proposed for cold-formed G450 steel sections. [ABSTRACT FROM AUTHOR]

Block shear strength of cold-formed steel bolted connections has been thoroughly investigated in the literature, although the behaviour of block shear with staggered holes has not been studied in detail. It is more complex and apparent that a combination of tension and inclined shear behaviour due to the presence of the staggered holes affects the shear strength and behaviour of the bolted connections. This paper presents an experimental program on the block shear behaviour of staggered hole bolted connections to provide a better understanding on the failure modes. A total of 24 tests using G450 sheets was conducted at the University of Sydney with 1.9 and 2.4 mm thicknesses. Digital Image Correlation (DIC) was employed to capture both the full field of the displacement and the block shear failure mode of the staggered hole bolted connections during testing. A comparison of the experimental strength with existing design equations for block shear with staggered holes in AISI S100:2016 and AS/NZS 4600:2018 is included in the paper. A calibrated Finite Element Model is then developed by the commercial program ABAQUS to validate against the test results and to further provide detailed insights which could not be seen in actual tests (i.e, stress and strain distributions). In the FE simulation, to study the whole range of deformation of the staggered hole bolted connections (i.e., elastic, plastic and fracture stages), a plasticity model and a ductile damage model are applied to the cold-formed steel sheets to represent various stress states in the steel during failure. [Display omitted] • Behaviour of block shear of bolted connections with staggered holes is thoroughly investigated. • An experimental program on the block shear behaviour of staggered hole bolted connections is conducted. • Digital Image Correlation (DIC) technique is employed to capture the displacement and failure mode of the staggered hole bolted connections. • A comparison of the experimental strength with existing block shear design equations for staggered holes in AISI S100:2016 and AS/NZS 4600:2018 is included. • Finite Element Models with proposed plasticity and ductile damage model are developed by ABAQUS program to validate against the test results. [ABSTRACT FROM AUTHOR]

The paper presents a series of four-point bending tests investigating global buckling of cold-rolled aluminium alloy channel beam members. These types of sections have been commercially fabricated in Australia using a roll-forming process as distinct from the usual extrusion process. A total of twenty specimens of three commercially available channel sections with two thicknesses and various lengths were tested at the University of Sydney. Mechanical properties of aluminium alloy 5052 material were reported on the basis of tests of tensile and compression coupons cut longitudinally from both flat and corner parts of the cross-sections. Prior to the testing of beams, initial geometric imperfections of each specimen were measured using a laser scanning method. A dual-actuator test rig was specially designed to maintain the load vertically applied through the shear centre of the channel section throughout the test. Flexural-torsional and distortional buckling modes were observed including interaction of these modes. The paper also details finite element (FE) models developed using the commercial ABAQUS software package to simulate the behaviour and ultimate member buckling capacities of cold-rolled aluminium alloy channel beams. The FE models with the incorporation of measured properties and actual imperfections are verified against the experimental results indicating good agreements. The test results are then compared with the design strength predictions from current specifications. The calibrated model results are laying the foundation for undertaking parametric studies and proposing new design rules for the global and distortional buckling capacities of these types of cold-rolled aluminium alloy channel sections in the subsequent work. Unlabelled Image [ABSTRACT FROM AUTHOR]

Experiments on screwed connections in shear were carried out at the University of Sydney using 2 or 3 self-drilling screws connecting high strength cold-formed steel sheets. Different types of screws and various thickness combinations were used in order to investigate the bearing and tilting failure behaviour of screwed connections. The results are compared against standards and specifications from Australia, USA and Europe. From the comparisons, revised design equations based on the Australian Standard/New Zealand AS/NZS 4600:2018 are proposed. The equations are verified using data from other international data sets of screwed connection experiments in shear. The data are used to calculate new capacity reduction factors, which are higher than the current factor in AS/NZS 4600:2018 for screwed connections in bearing and tilting. Based on the comparison, a revised capacity reduction factor is proposed. • An experimental program on screwed connections in high strength cold-formed steels in shear is carried out. • Different screw types and steel thicknesses are used to study the bearing and tilting failures of screwed connections. • The results are compared against standards and specifications from Australia, USA and Europe. • Revised design equations for design of screwed connections based on the Australian Standard AS/NZS 4600:2018 are proposed. • New capacity reduction factors for design of screwed connections in bearing and tilting are proposed in AS/NZS4600. [ABSTRACT FROM AUTHOR]

Cold-formed steel members are commonly perforated with elongated web openings in practice to allow more access for the building service systems. The presence of such extended web holes in the members, when subjected to high shear forces, influences the shear buckling characteristics, the shear failure modes and generally leads to a reduction of shear capacity as well. In order to provide a better insight into the shear behaviour of cold-formed members with elongated web cut-outs, this paper presents a numerical study using finite element method (FEM) models employing ABAQUS/Standard to investigate the elastic shear buckling and post-buckling behaviour of cold-formed members in the form of thin channel sections. A full non-linear FEM model is developed and calibrated against previous shear tests with elongated web holes carried out using a dual actuator test rig. Based on the successful calibration against the tests, a parametric investigation is conducted to extend the resulting database. Further, a new proposal for the Direct Strength Method (DSM) of design of perforated channels in shear with both non-elongated and elongated web holes is further validated by using the results from the parametric study. A comparison between the empirical approach (" q s " method) and the new DSM of design derived from the Vierendeel mechanism approach is also provided to enhance the applicability of the new proposal to different cases of perforated channel members in shear with a wider range of sectional dimension and thicknesses. Unlabelled Image [ABSTRACT FROM AUTHOR]

In the latest North American Specification S100:2016 Edition and the most up-to-date Australian/New Zealand Standard AS/NZS 4600:2018, the Direct Strength Method (DSM) shear design rules for unperforated channel sections have been adopted. To date, for perforated sections, there is no DSM design rule for shear in the current Specification/Standard while the conventional reduction factor method is still in use to calculate shear strengths for these sections. This paper summarises the test results in an experimental program aiming to determine the ultimate shear strengths of high strength cold-formed C-sections with square holes centrally cut from the webs. A total number of 24 tests were performed using lipped channel sections in which 18 tests were conducted with central square holes of variable thicknesses and sizes, and the remaining 6 were tested with no holes in the webs. Three different section thicknesses and square hole sizes were chosen for investigation in this study. In addition, Finite Element Method (FEM) analysis was initially developed to validate against test results, and the accurate results from the FEM were then employed in a parametric study for the extension of test data by varying the section thicknesses and the hole sizes. In the DSM shear design equations, two inputs namely the shear buckling load, V cr , and the shear yielding load, V y , are required. The numerical solutions for V cr for whole sections with central square holes have been proposed by first author in previous research studies. For V y in this paper, a new and simplified model is proposed based on net web areas. Recommendations for an extension to the DSM shear design rules for channel sections with square holes up to certain hole size limit are given. • An experimental program of high strength cold-formed steel channels with square holes in shear is carried out. • Numerical simulation using Finite Element Method (FEM) program is performed for test validation and parametric study. • Elastic shear buckling loads of channel sections with square holes are computed using numerical solutions. • A new simple and simplified equation based on net web area of the channel to calculate shear yield loads is proposed. • Extension of the DSM shear design rules is proposed for cold-formed channels with square openings up to hole size limit. [ABSTRACT FROM AUTHOR]

Cold-formed steel channels with web openings in shear have been thoroughly investigated mainly with circular and square holes. However, web cut-outs are likely to be enlarged along the span length of members due to a limited web depth to provide more access for the building services in practice. The design of cold-formed sections with elongated web holes in shear was investigated and retained in the AISI S100–16 and the AS/NZS 4600:2018 using the empirical approach. This paper presents an experimental investigation of perforated channel sections with rectangular and slotted web openings in shear using a dual actuator test rig to minimise the effects of bending moments and obtain the predominantly shear capacity with an aspect ratio up to 2.0. The commercially available plain C-lipped channel sections with a depth of 200 mm and a thickness of 1.5 mm were chosen with varying sizes of central cut-outs. A new strategy for determination of the shear yield loads (V y) together with the Vierendeel mechanism approach is presented in this study to propose a modified design for perforated channels with web openings having aspect ratios of holes up to 3.0 for the Direct Strength Method (DSM) of design of channel members in shear with elongated web openings. In addition, as required in the DSM method, the shear elastic buckling loads (V cr) are extracted from the linear elastic buckling analyses using finite element method in this paper. • An experimental investigation of channel sections with rectangular and slotted web openings in shear is performed. • A dual actuator test rig to minimise the effects of bending moments and obtain the predominantly shear capacity is used. • Shear elastic buckling loads are extracted from the linear elastic buckling analyses using finite element method. • New strategy for determination of the shear yield loads together with the Vierendeel mechanism approach is presented. • Direct Strength Method modified design rules for perforated channels with elongated web openings in shear are proposed. [ABSTRACT FROM AUTHOR]

Screws are commonly used as connectors in cold-formed steel structures as they can be drilled easily through thin sheet steels, allowing on-site assembly. However, in a connection undergoing shear and bending, while a screw may fail, other screws may be still in the elastic state. Therefore, investigation in the load-deflection response of screw connectors before failure is required for further understanding of complex screwed connections. Experiments and simulation are being carried out at the University of Sydney in order to investigate the behaviour of cold-formed steel connections with screw fasteners in shear. The screw model is built with solid deformable elements containing the screw threads. A plasticity model is applied to the steel sheets to represent different stress states of steel during failure. The model successfully simulates the different behaviour occurring simultaneously in the screwed connection tests: tearing and piling up of the steel sheets, end plate failure, tilting and fracture of the screws. [ABSTRACT FROM AUTHOR]

• An experimental program of cold-rolled aluminium alloy 5052-H36 channel sections is performed. • Energy dispersive X-ray spectroscopy technique is conducted for the chemical compositions. • Flat and corner tensile coupon tests are performed in cold-rolled aluminium channels. • New equations for corner properties of cold-rolled aluminium sections are proposed. • Residual stress measurements throughout cold-rolled aluminium C-sections are performed. In recent years, aluminium alloys have been paid more attention in the construction industry due to their attractive attributes such as light mass, high strength, easy recycling and high corrosion resistance. Traditionally, aluminium alloy sections used for structural applications have been formed by extrusion. Until recently, structural aluminium C- and Z- sections have been successfully cold-rolled from aluminium coil using existing rolling systems for cold-formed steel sections. During the cold-rolling process, plastic deformation at the corner regions results in strain hardening and associated enhancement of the yield stress. Also, the cold-rolling process may generate residual stresses around the cross-sections affecting the structural behaviour of members. It is therefore necessary to determine the mechanical properties and residual stresses caused by the cold-forming process. This paper describes an experimental program carried out at the University of Sydney to thoroughly investigate the distributions of mechanical properties and residual stresses throughout the cross-sections of cold-rolled aluminium C-sections. The experimental results provide an understanding of the magnitude and distribution of mechanical properties and residual stresses in cold-rolled aluminium sections, which are found to be different from those in cold-rolled steel and stainless-steel sections. Based on the experimental findings, the longitudinal membrane residual stresses are very small up to approximately 3% of yield stresses and may be neglected, whereas the longitudinal bending residual stresses are measured up to 30% of yield stresses. [ABSTRACT FROM AUTHOR]

The direct strength method (DSM) is a newly developed design method for cold-formed steel members due to its reliability and consistency. It has been well developed and incorporated in the North American Specification and the Australian/New Zealand Standard for the design of cold-formed steel members under compression, bending, and recently, in shear. To date, there are no DSM rules for the design of cold-formed members under localized loading resulting in the web-crippling phenomenon. Recent literature has attempted to propose the DSM design equations for four localized loading cases including the interior one-flange (IOF), end one-flange (EOF), interior two-flange (ITF), and end two-flange (ETF) loading cases specified in the design specifications/standards. However, these proposed DSM equations were calibrated differently depending on the types of loading cases and geometric shapes of the cross-sections by varying coefficients and exponents in the DSM equations. In this paper, consistent and simplified DSM equations previously proposed by the authors are explained and calibrated for use in the design specifications/standards. They include new plastic mechanism models developed for determining the yield load and also cover the design of sections in the inelastic reserve range as observed. Detailed explanations of the yield load (Py) component and references to computing the buckling load (Pcr) component are given. A design example is also included. [ABSTRACT FROM AUTHOR]

In the current standards/specifications for cold-formed steel structures, the direct strength method (DSM) has not been developed for the shear strengths of perforated members, which is currently based on an empirical design approach using a qs factor. To extend the DSM design to members in shear with various hole shapes and sizes, new design procedures have been developed to determine shear loads including the elastic shear buckling load (Vcrh), shear yield load (Vyh), and ultimate shear strength (Vn). Vcrh can be calculated via a linear approximation for buckling coefficients (kv) based on the hole and section dimensions. Vyh can be computed based on a theoretical Vierendeel mechanism or a proposed alternative simplified model to permit an easier implementation in design checks. Vn can be determined using proposed DSM shear curves for members with and without full-transversely stiffened webs. To validate the new DSM approach, a collection of reliable historical experiments in perforated sections under shear was used for strength comparison. The experimental shear strengths were also further used for the calibration of the DSM-based proposal to determine the resistance factor (ϕ) for shear design, which is traditionally based on the LRFD methodology. [ABSTRACT FROM AUTHOR]

Thin-walled sections under localised loading may lead to buckling of the sections. This paper briefly introduces the development of the Finite Strip Method (FSM) for buckling analyses of thin-walled sections under localised loading for general end boundary conditions. This method is benchmarked against the Finite Element Method (FEM). For different support and applied loading conditions, different functions are required for flexural and membrane displacements. In Part 1- Pre-buckling described in the companion paper, the analysis provides the computation of the stresses for use in the buckling analyses in this paper. Numerical examples of buckling analyses of thin-walled sections under localised loading with different end boundary conditions are also given in the paper in comparison with the FEM. [ABSTRACT FROM AUTHOR]

The Finite Strip Method (FSM) for pre-buckling analysis of thin-walled sections under localised loading has been developed for general end boundary conditions. For different boundary conditions at supports and locations of applied loads, different displacement functions are required for both flexural and membrane displacements. As the stresses are not uniform along the member due to localised loading, the pre-buckling analysis also requires multiple series terms with orthogonal functions. This paper briefly summaries the displacement functions used for different boundary conditions. In addition, the theory of the FSM for pre-buckling analysis of thin-walled sections under localised loading with general end boundary conditions is developed. The analysis is subsequently benchmarked against the Finite Element Method (FEM) using software package ABAQUS/Standard. The results from this pre-buckling analysis are deflections (pre-buckling modes) and membrane stresses which are used for the buckling analysis described in Part 2 - Buckling in the companion paper. [ABSTRACT FROM AUTHOR]

In this paper, a total of 254 results comprising 30 shear tests and 224 finite element (FE) analysis results are reported. Simply supported test specimens of cold-formed steel (CFS) channels with aspect ratios of 1.0 and 1.5 were tested. For comparison, specimens with unstiffened web holes and plain webs were also tested. A nonlinear elastoplastic FE model was then developed and validated against the experimental results. Using the validated FE model, a parametric study was conducted to investigate the effect of various influential parameters on the shear capacity of such CFS channels. The test results show that for a channel with edge-stiffened web holes, the shear capacity increased by 14.5% on average when compared with that of a channel with unstiffened web holes. The test and FE results were compared against the design predictions. Upon comparison, it was found that the design rules of CFS channels with unstiffened web holes in accordance with the AISI and AS/NZS can be unconservative by 7% while calculating the shear capacity of CFS channels with edge-stiffened web holes. Therefore, a suitable design formula in the form of a shear capacity reduction factor was proposed for CFS channels with edge-stiffened web holes. [ABSTRACT FROM AUTHOR]

A thermodynamics-based coupled damage-plasticity model for high strength cold-reduced steel is developed on the basis of a generic form, allowing the use of any yield criterion and damage evolution rule. The model possesses essential features of ductile failure, including large plastic deformation prior to fracture and the effects of both triaxiality and Lode angle on the failure. In conjunction with theoretical development, experimental work for both furthering the understanding of ductile fracture in high strength cold-reduced steel and validation of the proposed model under different loading conditions is also performed. In particular, advanced non-contact measurement techniques based on Digital Image Correlation (DIC) are used not only for characterising the material failure/data in both pre- and post-peak phases but also for calibration of parameters and validation of the proposed model. While the pre-peak hardening responses with homogeneous deformation can be described by a nonlinear hardening rule, in the post-peak regime, localisation of deformation before complete fracture requires the use of energy in both characterisation of the material failure and calibration of the model. In this sense, the essential work of fracture obtained from the experiments is linked with parameters controlling the fracture of the material and also used for a simple regularisation technique based on the concept of smeared deformation. The model responses are validated against experimental data in terms of both macro responses and evolving failure patterns, demonstrating good potential for applications in failure analysis of structures made of high strength cold-reduced steel. [ABSTRACT FROM AUTHOR]

This paper explores the use of an explicit solver available in ABAQUS/Explicit to simulate the behaviour of blind bolted endplate connections between composite beams and concrete-filled steel tubular (CFST) columns. Main aspects of the explicit analysis such as solution technique, blind bolt modelling, choice of element type and contact modelling are discussed and illustrated through the simulation of a large-scale test on the considered joint. The mass scaling option and smooth step amplitude are very effective tools to speed up the explicit simulation. Shell elements can be used in modelling the I-beam due to their computational efficiency and accuracy in capturing local buckling effects. With a proper control of the loading rate, the explicit analysis can provide accurate and efficient predictions of the quasi-static behaviour of the bolted endplate composite connections. [ABSTRACT FROM AUTHOR]

Experimental tests have previously shown that the strength of bolted moment-connections between cold-formed steel channel members, where the connections are formed through an array of bolts in the web, is dependent on the length of the bolt-group. This reduced strength has been observed in tests on portal frame joints as well as overlapped purlin joints. For a long bolt-group length, an upper bound would be the full in-plane major axis moment-capacity of the section, which can be predicted using the conventional Direct Strength Method (DSM). For a short bolt-group length, in the order of the depth of the section, a reasonable lower bound to the reduced strength can be predicted by using the DSM, modified to include the effect of the bimoment at the connection. In this paper, a parametric study is performed covering sections of different values of slenderness. [ABSTRACT FROM AUTHOR]

• Eighty one experimental tests on the design strength of power-actuated fasteners (PAFs) in single shear connections are presented. • Modes of failure for both the PAFs and the connected material were examined so to provide an understanding of the structural performance of nailed single lap connections. • The predominant mode of failure for all tested specimens was tilting and bearing or head shearing induced by tilting of the PAFs. • The tests results were compared against the design strengths as per the AS/NZS for both the screws and PAFs. • Based on the test strengths and failure modes, the existing design provisions for screw connections in AS/NZS were adjusted and applied to PAF connections. This paper presents the results of 81 experimental tests on the design strength of power-actuated fasteners (PAFs) in single shear connections for a light gauge steel framing (LGSF), as an alternative to self-drilling screws for selective uses. This type of connection can be employed to install a reinforcing plate on one or both sides of the frame, to connect steel strap cross bracing to framing, as well as for many other applications. These power-actuated fasteners present a very efficient and practical solution which can increase productivity and work quality by replacing time consuming screw connections. In this study, two different steel grades (G300 and G550), along with three different steel sheet configurations were investigated. Modes of failure for both the PAFs and the connected material were examined so to provide an understanding of the structural performance of nailed single lap connections and develop design recommendations and proposed formulae. The investigation covers a wide range of steel gauges (0.75 mm, 0.95 mm and 1.15 mm), commonly used in LGSF residential and commercial applications. Two groups of tests were performed. The first group of tests was conducted to determine the shear strength of connectors with two types being tested. The second tests series were carried out in various steel grade and gauge configurations for assembled connections. The results of this research and the proposed design formula can be used to establish the strength prediction model for power-actuated fasteners (PAFs) embedded into LGSF. [ABSTRACT FROM AUTHOR]

This paper presents experimental observations of cold-reduced G450 sheet steel subjected to shear. A total of 28 shear specimens of 1.5 mm and 3.0 mm thicknesses were tested. Two different test geometries were used to examine the shear state. The Digitial Image Correlation (DIC) technique was utilised to obtain the full fields of displacement and strain during the test execution. Strain distribution and evolution are used for quantifying shear stress- shear strain evolution inside the shear band. In terms of stress consideration, 0.35% proof shear strain is proposed to determine a yield stress in shear. The experimental results show that the cold-reduced G450 sheet steel follows von Mises criterion at yield (0.577), but possesses a higher ratio for the ultimate shear strength to tensile strength. Although the steel shows lower yield stress in the longitudinal rolling direction than that in the transverse, it possesses higher ultimate strength and ductility. [Display omitted] • An experimental program on shear yielding and fracture of high strength G450 steel is performed. • Digital Image Correlation (DIC) is used to obtain the full fields of displacement and strain. • Strain distribution and evolution are used for quantifying shear stress-shear strain evolution. • Cold-reduced G450 sheet steel is confirmed to follow von Mises criterion at shear yield. • Proof yield stress at 0.35% shear strain is proposed to be consistent with 0.2% strain in tension. [ABSTRACT FROM AUTHOR]