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Highlights • 16 fixed-ended cold-formed stainless steel equal-leg angle section columns have been tested. • Numerical models have been validated against tests and used to perform parametric studies. • The column flexural-torsional buckling behaviour has been systematically investigated. • Current international design codes and other recent proposals have been described and discussed. • The accuracy of each approach has been evaluated against test and FE results. Abstract The flexural-torsional buckling behaviour of fixed-ended cold-formed stainless steel equal-leg angle section columns was experimentally and numerically investigated in this paper. The testing programme was conducted on two press-braked austenitic stainless steel equal-leg angle sections, and involved material testing, initial imperfection measurements and sixteen fixed-ended column tests. The test setup and procedure, together with the key experimental results, load–mid-height torsional rotation histories and flexural-torsional buckling failure modes, were fully reported. Finite element models were then developed to simulate the fixed-ended cold-formed stainless steel equal-leg angle section column tests, and the numerical structural responses and failure modes were shown to match well with the corresponding experimental observations. The validated finite element models were then utilised to carry out parametric studies to generate an extensive pool of numerical data on fixed-ended cold-formed stainless steel equal-leg angle section columns susceptible to flexural-torsional buckling. The load-carrying capacities derived from both the experiments and FE modelling were compared with the resistance predictions from the established design standards in Europe, America, and Australia/New Zealand and a recently proposed direct strength method. The comparison results generally indicated that the existing design codes unduly underestimate the flexural-torsional buckling resistances of fixed-ended cold-formed stainless steel equal-leg angle section columns, while the direct strength method substantially improves the design accuracy on average, but with many overpredicted resistances, indicating that further improvements are generally required. [ABSTRACT FROM AUTHOR]

Six aluminum alloy tensile coupon tests were carried out and stress–strain curves obtained from tests were compared with a Ramberg–Osgood model. Comparison showed that the Ramberg–Osgood model can precisely describe stress–strain relationship of 6063-T5 aluminum alloy. Totally, 10 axial compression tests on thin-walled aluminum alloy members with four stiffened closed-section were carried out. Local buckling occurred in all specimens eventually. The axial displacement, lateral deflection, strain development and failure modes of the tested specimens were recorded. A finite element method (FEM) model was presented to simulate local buckling behaviors of the tested columns under axial load. The ultimate strength, strain development and failure modes obtained from FEM agreed well with the test results. Current design codes on aluminum alloy structures, such as the American aluminum design manual (AA), the European code (EC9), Chinese design specifications for aluminum structures (GB50429), the North American Specification for the design of cold-formed steel structural members (AISI) and the direct strength method (DSM), were used to calculate the ultimate strength of the tested columns. Comparison showed that current design codes overestimated the ultimate strength of stiffened closed-section thin-walled aluminum alloy columns under axial compression loads. [ABSTRACT FROM AUTHOR]

Thin-walled columns with section are used widely as columns in aluminum alloy framed structures, offering high strength-to-weight ratios and convenience in connection with maintaining walls. In this paper, thin-walled aluminum alloy columns with section were studied experimentally and numerically to investigate the buckling behavior and to assess the accuracy of current design methods. A finite element model (FEM) was developed and used to perform parametric studies after being verified by tests. Effects of plate thickness on elastic buckling stress was studied using finite strip method (FSM) and to find the potential buckling failure mode at a given length. Tested ultimate strengths were compared with those predicted by the current American, European and Chinese specifications on aluminum alloy structures and the Direct Strength Method (DSM) on thin-walled structures. Following reliability analysis, the design strength predicted by current design specifications were found to be generally conservative, whereas DSM offered more accurate results. [ABSTRACT FROM AUTHOR]

The global buckling behaviour of hot-rolled stainless steel channel section beam–columns under combined compression and minor-axis bending moment has been studied based on testing and numerical modelling and reported in this paper. A testing programme was conducted on ten hot-rolled austenitic stainless steel channel section beam–columns, with five buckling towards webs and the other five buckling towards flange tips. This was followed by a numerical modelling programme, in which finite element models were firstly developed and validated against the test results and then used to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions, member effective lengths and loading combinations. The test and numerical results were adopted to assess the current design interaction curves given in the European code and American guide, both of which were found to result in inaccurate and scattered failure load predictions. The inaccuracy of the codified design interaction curves stems from the inaccurate end points (i.e. the member resistances under pure compression and pure bending) and the inappropriate shape. To address these shortcomings, a new design interaction curve was developed firstly through the adoption of more accurate end points and secondly through the derivation of a more proper shape. The proposed design interaction curve was shown to yield accurate and consistent failure load predictions for hot-rolled stainless steel channel section beam–columns. The reliability of the new proposal was also confirmed by means of statistical analyses. • The buckling behaviour of hot-rolled stainless steel channel section beam–columns is studied. • Ten beam–column tests were conducted. • FE models were firstly developed and validated against the test results and then adopted to perform parametric studies. • The codified design interaction curves were assessed, indicating inaccuracy. • A new design interaction curves was proposed, with the accuracy and reliability demonstrated. [ABSTRACT FROM AUTHOR]

A thorough testing and numerical modelling programme has been conducted to investigate the minor-axis flexural buckling behaviour and resistances of pin-ended hot-rolled stainless steel channel section columns. The testing programme included material coupon tests, membrane residual stress measurements, initial global and local geometric imperfection measurements and ten pin-ended channel section column tests about the minor principal axis. A membrane residual stress predictive model was developed based on the measured data. The testing programme was followed by a numerical modelling programme; finite element models were developed to simulate the test results and then adopted to perform parametric studies to generate further numerical data on hot-rolled stainless steel channel section columns over a wide range of cross-section dimensions and member effective lengths. The obtained test and numerical data were then adopted to assess the accuracy of relevant design rules for hot-rolled stainless steel channel section columns failing by flexural buckling about the minor principal axis, as given in the European code and American design guide. The assessment results revealed that (i) the European code yields many unsafe flexural buckling resistance predictions and (ii) the American design guide yields overly conservative and scattered flexural buckling resistance predictions. Finally, a revised Eurocode buckling curve was proposed and shown to offer accurate, consistent and safe-sided flexural buckling resistance predictions for hot-rolled stainless steel channel section columns over the whole considered range of member non-dimensional slendernesses. The reliability of the revised Eurocode buckling curve was also confirmed using statistical analyses based on EN 1990. • Flexural buckling of hot-rolled stainless steel channel section columns was studied. • Ten pin-ended hot-rolled stainless steel channel section column tests were conducted. • Numerical modelling and parametric studies were conducted. • TThe accuracy of the relevant codified design rules was assessed. • A new improved design method was proposed. [ABSTRACT FROM AUTHOR]

The flexural-torsional buckling behaviour and resistances of pin-ended hot-rolled stainless steel angle section columns have been studied in the present paper, based on laboratory testing and numerical modelling. The testing programme adopted four hot-rolled stainless steel angle sections and included initial global and torsional geometric imperfection measurements and twelve pin-ended column tests. The key obtained test results, including the failure loads and deformations at the failure loads, the load–mid-height lateral deflection curves and failure modes, were fully reported and discussed. Strong interaction between flexural-torsional buckling about the major principal axis and flexural buckling about the minor principal axis was observed for each pin-ended hot-rolled stainless steel angle section column specimen during and upon testing. The testing programme was followed by a numerical modelling programme; finite element models were developed and validated against the test results, and afterwards used to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions and member lengths. On the basis of the experimentally and numerically obtained data, the accuracy of the codified design methods, as adopted in Europe, America and Australia/New Zealand, and a recently proposed DSM-based design approach for pin-ended hot-rolled stainless steel angle section columns susceptible to flexural-torsional buckling, were evaluated. Overall, it may be concluded that (i) all the three considered design codes result in conservative flexural-torsional buckling resistance predictions, (ii) the current European code leads to more accurate resistance predictions for pin-ended columns with non-slender hot-rolled stainless steel angle sections, but a lower degree of design accuracy for pin-ended columns with slender hot-rolled stainless steel angle sections, in comparison with the American specification and Australian/New Zealand standard, and (iii) the DSM-based design approach yields substantially improved resistance predictions, due to the rational consideration of the length-dependent characteristic of flexural-torsional buckling and the interaction of flexural-torsional buckling with minor-axis flexural buckling, but with many predictions lying on the unsafe side. • The flexural-torsional buckling behaviour of pin-ended hot-rolled stainless steel angle section columns was studied. • Twelve pin-ended hot-rolled stainless steel angle section column tests were conducted. • FE models were firstly developed and validated against the test results, and then used to conduct parametric studies. • Based on the test and FE results, the current design provisions were assessed and their shortcomings were highlighted. [ABSTRACT FROM AUTHOR]

The buckling behaviour and resistances of press-braked stainless steel channel section beam-columns under combined compression and minor-axis bending have been studied in the present paper through laboratory testing and numerical modelling. The testing programme adopted two press-braked stainless steel channel sections and included initial global and local geometric imperfection measurements and ten beam-column tests. Two types of failure mode, namely 'C'-orientation buckling (indicating that failure specimens buckled towards the web) and 'reverse C'-orientation buckling (signifying that failure specimens buckled towards the flange tips), were observed upon testing. The testing programme was followed by a numerical modelling programme; finite element models were developed and validated against the test results and then adopted to perform parametric studies to generate further numerical data on press-braked stainless steel channel section beam-columns over a wide range of cross-section dimensions, member effective lengths and loading combinations. The obtained experimental and numerical data were employed to assess the accuracy and consistency of the relevant codified design rules for press-braked stainless steel channel section beam-columns, as given in the European code, American specification and Australian/New Zealand standard. The results of assessment revealed that the European code yields many unsafe resistance predictions for Class 1 and 2 press-braked stainless steel channel section beam-columns but overly conservative resistance predictions for Class 3 press-braked stainless steel channel section beam-columns, although the resulting overall design accuracy is good, but with a high level of scatter of the resistance predictions. Compared with the European code, the American specification and Australian/New Zealand standard result in slightly more accurate resistance predictions for press-braked stainless steel channel section beam-columns with buckling in the 'C' orientation, but lead to significantly more conservative predicted resistances for press-braked stainless steel channel section beam-columns with buckling in the 'reverse C' orientation. In terms of the design consistency, the American specification and Australian/New Zealand standard were shown to result in more consistent resistance predictions (regardless of cross-section dimensions and buckling orientations) than their Eurocode counterpart. • The buckling behaviour and resistances of press-braked stainless steel channel section beam-columns were studied. • Ten press-braked stainless steel channel section beam-column tests were performed. • FE models were developed and validated against the test results and then employed to conduct parametric studies. • The codified design interaction formulae were evaluated, based on the test and FE results. [ABSTRACT FROM AUTHOR]

The minor-axis flexural buckling behaviour and strengths of pin-ended press-braked stainless steel channel section columns have been investigated in the present paper through laboratory testing and numerical modelling. An experimental programme was firstly conducted, and included initial global and local geometric imperfection measurements and twelve pin-ended column tests about the minor principal axis. The key obtained test results, including the failure loads, the mid-height lateral deflections at the failure loads, the load–mid-height lateral deflection curves and the failure modes, were reported and discussed in detail. The experimental programme was followed by a numerical modelling programme; finite element models were developed to simulate the test responses and then adopted to perform parametric studies to generate further numerical data on press-braked stainless steel channel section columns over a wide range of cross-section dimensions and member effective lengths. The obtained experimental and numerical data were employed to assess the accuracy of the relevant design rules for press-braked stainless steel channel section columns failing by flexural buckling about the minor principal axis, as given in the European code, American specification, Australian/New Zealand standard and SCI design manual. The results of the assessment indicated that (i) the European code yields unsafe flexural buckling strength predictions for those relatively short and intermediate press-braked stainless steel channel section columns with member non-dimensional slendernesses less than around 1.0, (ii) the American specification leads to unsafe predictions of flexural buckling strength for press-braked stainless steel channel section columns over the whole considered range of member non-dimensional slendernesses up to 3.0, and (iii) the Australian/New Zealand standard and the SCI design manual result in lower levels of design accuracy than the European code and American specification, but with significantly reduced number of unsafe flexural buckling strength predictions. • The minor-axis flexural buckling behaviour of press-braked stainless steel channel section columns was studied. • Twelve pin-ended press-braked stainless steel channel section column tests were carried out. • FE models were firstly developed and validated against the test results, and then adopted to conduct parametric studies. • The accuracy of the relevant codified design rules was evaluated, based on the test and FE results. [ABSTRACT FROM AUTHOR]

• The flexural-torsional buckling behaviour of fixed-ended press-braked S690 high strength steel angle columns was studied. • Twelve compression tests of fixed-ended press-braked S690 high strength steel angle columns were carried out. • FE models were developed and validated against the test results, and then adopted for parametric studies. • The accuracy of the codified design rules and a new DSM-based design approach was evaluated. The flexural-torsional buckling behaviour and resistances of fixed-ended press-braked S690 high strength steel angle section columns have been studied based on testing and numerical modelling, and reported in this paper. A testing programme, employing four different equal-leg angle section sizes, was firstly conducted, and comprised material tensile coupon tests, initial global and torsional geometric imperfection measurements and twelve fixed-ended column tests. The column test setup and procedures were thoroughly presented, and the key obtained test results, including the failure loads and deformations at the failure loads, load–end shortening curves, load–mid-height torsional rotation curves and failure modes, were fully reported and discussed. This was followed by a numerical modelling programme, where finite element models were initially developed to simulate the experimental responses and then adopted to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions and member lengths. The obtained test and numerical data were then used to evaluate the accuracy of the relevant codified design rules, given in the European code, North American specification and Australian/New Zealand standard, and a recently proposed DSM-based design approach. The results of the evaluation revealed that all the codified design rules yield excessively conservative and scattered flexural-torsional buckling resistance predictions for fixed-ended press-braked S690 high strength steel angle section columns, while the DSM-based design approach leads to substantially improved resistance predictions, owing to the rational consideration of the length-dependent characteristic of flexural-torsional buckling and the interaction of flexural-torsional buckling with minor-axis flexural buckling. [ABSTRACT FROM AUTHOR]

A thorough testing and numerical modelling programme has been conducted to investigate the flexural buckling behaviour and strengths of pin-ended hot-rolled stainless steel angle section columns. The testing programme adopted three hot-rolled stainless steel equal-leg angle sections, and included 12 pin-ended column tests about the minor principal axis as well as supplementary initial geometric imperfection measurements on the column specimens. The testing programme was accompanied by a parallel numerical modelling programme, including a validation study, where finite element models were developed and validated against the test results, and a parametric study, where the validated finite element models were employed to generate additional numerical data over a broad spectrum of cross-section dimensions and member effective lengths. The test and numerical data were then adopted to evaluate the accuracy of the relevant design rules, as given in the European code and American design guide, for pin-ended hot-rolled stainless steel angle section columns prone to flexural buckling about the minor principal axis. On the basis of the evaluation results, it can be concluded that (i) the European code results in overall accurate and consistent flexural buckling strength predictions, but many of the predictions for short and intermediate columns with member non-dimensional slendernesses less than around 1.0 are unsafe, and (ii) the American design guide leads to unduly conservative and scattered flexural buckling strength predictions. Finally, a new design approach was developed through modifications to the Eurocode design rules, and shown to offer accurate, consistent and safe-sided flexural buckling strength predictions for pin-ended hot-rolled stainless steel angle section columns over the whole considered range of member non-dimensional slendernesses up to 4.0. The reliability of the new design approach was confirmed by means of statistical analyses according to EN 1990. • The flexural buckling behaviour and strengths of pin-ended hot-rolled stainless steel angle section columns were examined. • A total of 12 pin-ended column tests about the minor principal axis were conducted. • FE models were developed and validated against the test results, and then used to conduct parametric studies. • The relevant codified design rules were evaluated based on the test and FE data, indicating inaccuracy. • A new design approach was proposed, and shown to yield accurate, consistent and safe flexural buckling strength predictions. [ABSTRACT FROM AUTHOR]

• Material responses and local buckling behaviour of press-braked stainless steel angle and channel sections were studied. • Eight stub column tests and ten bending tests on press-braked stainless steel angle and channel sections were conducted. • Nonlinear FE models were developed and validated against test results, and then adopted to perform parametric analysis. • Current design codes were assessed against the test and numerical results, indicating undue conservatism. • The continuous strength method was evaluated and shown to yield precise and consistent cross-section capacity predictions. This paper reports an experimental and numerical investigation into the local stability of press-braked stainless steel angle and channel sections. The experimental programme was performed on two equal-leg angle sections and two plain channel sections, and included material testing, initial local geometric imperfection measurements, eight stub column tests and ten laterally restrained beam tests (about the geometric axes for angle sections and minor principal axes for channel sections). This was supplemented by a numerical simulation programme, where finite element models were firstly established to replicate the test structural responses and then employed to derive further numerical data through parametric studies. The results obtained from the structural testing and numerical modelling were adopted to evaluate the accuracy of the codified local buckling design provisions established in America, Europe and Australia and New Zealand. The evaluation results revealed that all the design codes greatly underestimate the cross-section resistances of press-braked stainless steel equal-leg angle and plain channel section stub columns and laterally restrained beams, mainly attributed to the neglect of the pronounced material strain hardening effect of stainless steel in the design. The continuous strength method (CSM) is an advanced deformation-based design method, allowing for a rational utilisation of material strain hardening in determining cross-section resistances, and its scope of application has been recently extended from doubly-symmetric (I- and tubular) sections to mono-symmetric and asymmetric (angle, channel and T-) sections. Quantitative evaluation of the CSM was conducted through comparing the predicted cross-section resistances against the experimental and numerical results. The CSM was found to yield substantially more accurate and consistent design cross-section resistances for press-braked stainless steel equal-leg angle and plain channel section stub columns and laterally restrained beams than the established design codes. [ABSTRACT FROM AUTHOR]

Abstract The present paper shows an experimental and numerical modelling investigation of the flexural-torsional buckling behaviour and load-carrying capacities of fixed-ended hot-rolled austenitic stainless steel equal-leg angle section columns. The testing programme was conducted on four austenitic stainless steel angle sections and involved material testing, initial global and torsional imperfection measurements and sixteen fixed-ended column tests. This was followed by a numerical simulation study, where the numerical models were firstly developed to validate against the experimental data and then utilised to perform numerical parametric studies to generate additional results over a broader range of member lengths and cross-section geometric dimensions. The derived test and finite element results were carefully analysed and then utilised to evaluate the accuracy of the established design rules in Europe, America and Australia/New Zealand. Comparisons of the failure loads derived from the experimental and numerical studies with the corresponding codified flexural-torsional buckling strength predictions revealed an unduly high level of conservatism and scatter. Extension of the direct strength method to carbon steel equal-leg angle section columns has been recently made, and the applicability of the approach to fixed-ended hot-rolled austenitic stainless equal-leg steel angle section columns was also assessed. The new approach was generally shown to yield more precise flexural-torsional buckling resistance predictions than the existing design standards, but a large portion of the predictions were unsafe, indicating that further improvements are required. Highlights • 16 fixed-ended hot-rolled austenitic stainless steel equal-leg angle section columns have been tested. • FE models have been validated against tests and used to perform parametric studies. • Current international design codes and other recent proposals have been described and discussed. • The accuracy of each approach has been evaluated against test and FE results. [ABSTRACT FROM AUTHOR]

Shear buckling behaviors of web-post in a Castellated Steel Beam (CSB) with hexagonal web openings under vertical shear were investigated using finite element method. Through treating the upper part of the web-post as a free body under horizontal shear force, whose shear buckling strength can be calculated by the thin-plate shear buckling theory, design equations for the vertical shear buckling strength of the web-post were proposed. Parameters that affected the vertical shear buckling strength of the web-post were studied, which were the opening height to web thickness ratio h 0 / t w , the web-post width to web thickness ratio e / t w , the web height of Tee-section above the opening to the web thickness h f / t w , the web thickness t w and the incline angle of the opening edge α . After obtaining the vertical shear buckling strength of a CSB through finite element model, the shear buckling coefficient k can be obtained through inverse analysis. Research results showed that k decreased non-linearly with the increase in e / t w and h f / t w and it increased linearly with the increase in α and h 0 / t w . Practical calculating method for k was proposed based on parameter analysis results. The vertical shear buckling strength of the web-post calculated using the proposed shear buckling coefficient k agreed well with that obtained from the finite element simulation. For the proposed method was based on the elastic buckling of the web-post, it overestimated the shear buckling strength when the web-post buckled in the elastic–plastic state. [ABSTRACT FROM AUTHOR]

Web-post buckling behaviors of fully and partially protected cellular steel beams at elevated temperatures in a fire were investigated through verified finite element models. The partially protected cellular steel beam represented a protected cellular steel beam with the hole edge left unprotected. The temperature distribution in the web-post was non-uniform, even for the unprotected CSB and the fully protected CSB. The fire resistance time of a CSB increased linearly with the increase in fire coating thickness. However, for the partially protected cellular steel beam, the temperature gradient in the web-post becomes greater with the increase in the fire protection thickness. And with the increase in the fire protection thickness, the increment in the fire resistance time decreased. Additional thermal stress occurred due to the non-uniform thermal strain in the web-post. When web-post buckled, the principle compression stress in the web-post decreased suddenly. The stress at the center of the web-post could change from compression to tension due to the membrane action caused by the large buckling deformation. [ABSTRACT FROM AUTHOR]

Failure modes of the thin-walled aluminum alloy column with irregular shaped cross section at ambient temperature and elevated temperatures in a fire were studied using a verified finite element model. The studied failure modes included the sectional yielding, interaction of local buckling and sectional yielding, interaction of local and global buckling, and global buckling. The finite element model was verified by experimental results from the ultimate strength, the failure modes and the failure deformation. Deformation shape along the column failed by different failure modes was presented. Stresses development at the middle span section was greatly affected by the failure modes. Ultimate strengths of a series of aluminum alloy columns with different length, cross section dimension were analyzed by the finite element analysis and current design codes at different temperatures in a fire. The current design codes greatly underestimated the ultimate strength of the thin-walled aluminum alloy column with irregular shaped cross section. Design method provided by EN1999-1-2 can give an accurate prediction of the ultimate strength of a short thin-walled aluminum alloy column with irregular shaped cross section at temperatures lower than 250 °C. A modification to the design method in EN1999-1-2 was proposed for predicting the ultimate strength of the aluminum alloy column with length longer than 500 mm and at temperatures higher than 250 °C. Ultimate strength predicted by the modified equation agreed well with finite element analysis results. [ABSTRACT FROM AUTHOR]