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The flexural buckling behaviour and resistances of press-braked stainless steel Z-section columns are investigated in this paper, based on experiments and numerical modelling. An experimental investigation was conducted on two press-braked stainless steel Z-sections and included material testing, initial geometric imperfection measurements and twelve fixed-ended column tests. Minor-axis flexural buckling was observed for all press-braked stainless steel Z-section column specimens upon testing. The key obtained fixed-ended column test results, including failure loads, load–deformation histories and failure modes, were fully reported. Following the experimental investigation, a numerical investigation was performed, with finite element models developed to validate against the fixed-ended column test results and then used to conduct parametric studies to generate additional numerical data. On the basis of the test and numerical data, the relevant buckling curves, as specified in the European code, American specification and Australian/New Zealand standard, were evaluated and shown to provide accurate and consistent flexural buckling resistance predictions for press-braked stainless steel Z-section columns. • The flexural buckling behaviour of press-braked stainless steel Z-section columns was studied. • Twelve fixed-ended column tests were conducted. • FE models were developed to validate against the test results and then used to perform parametric studies. • The codified buckling curves were assessed, showing good design accuracy and consistency. [ABSTRACT FROM AUTHOR]

• 1. The local–flexural interactive buckling of press-braked stainless steel slender channel section columns is studied. • 2. Ten pin-ended column tests are conducted. • 3. FE models are developed and validated against the test results and then adopted to conduct parametric studies. • 4. The codified design rules are assessed and shown to yield inaccurate interactive buckling resistance predictions. • 5. A new design method is proposed, showing improved design accuracy. The present paper reports experimental and numerical studies of the local–flexural interactive buckling behaviour and resistance of press-braked stainless steel slender channel section columns. A testing programme was firstly performed, including tensile coupon tests, initial geometric imperfection measurements and ten pin-ended column tests. The pin-ended column test setup, procedures and results were fully reported and analysed. The progression of local buckling and flexural buckling was discussed in detail. Following the testing programme, a numerical modelling programme was conducted, where finite element models were developed to replicate the test responses and then employed to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions and member effective lengths. The obtained test and numerical data were employed to assess the accuracy of the relevant design rules for press-braked stainless steel slender channel section columns, as set out in the European code, American specification and Australian/New Zealand standard. The assessment results revealed that the European code leads to conservative and scattered interactive buckling resistance predictions, while the American specification and Australian/New Zealand standard result in many unsafe and scattered interactive buckling resistance predictions. A new design approach was then developed, based on the Eurocode column buckling curve and the continuous strength method, and shown to lead to accurate, consistent and safe interactive buckling resistance predictions for press-braked stainless steel slender channel section columns. The reliability of the new design approach was confirmed by means of statical analyses. Besides, the relevant design rules for press-braked carbon steel slender channel section columns, as given in the North American specification, were assessed, and shown to result in unsafe though consistent interactive buckling resistance predictions, when used for their stainless steel counterparts. [ABSTRACT FROM AUTHOR]

• The flexural buckling of press-braked S960 ultra-high strength steel angle section columns have been studied. • Initial geometric imperfection measurements and 12 pin-ended column tests have been conducted. • Flexural buckling in both the 'C' orientation and 'reverse C' orientation has been investigated. • FE models have been developed and validated against the test results, and then used to conduct parametric studies. • The applicability of the relevant codified design provisions has been evaluated, based on test and FE results. The structural performance and compression resistances of pin-ended press-braked S960 ultra-high strength steel (UHSS) angle section columns have been studied based on experiments and numerical modelling, and are reported in the present paper. An experimental programme was firstly performed on two series of press-braked S960 UHSS angle section column specimens, with each series containing six specimens of the same cross-section dimension but different member lengths, and included initial torsional and global geometric imperfection measurements and pin-ended column tests. The detailed pin-ended column test setup, procedures and results, including the failure loads, deformations at the failure loads, load–mid-height lateral deflection curves and failure modes, were fully reported. It is worth noting that two distinct flexural buckling orientations about the minor principle axis were observed from the tests, namely 'C' orientation (indicating that the failed column specimens buckled towards the angle corners) and 'reverse C' orientation (signifying that the failed column specimens buckled towards the angle tips). A numerical modelling programme was then followed; finite element (FE) models were firstly developed to replicate the test responses, and then adopted to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions and member lengths. Given that the current design codes for steel structures, as used in Europe, Australia/New Zealand and North America, are only applicable to members and joints with material grades up to S700 (or S690), the relevant codified design provisions for press-braked S700 (or S690) high strength steel angle section columns were evaluated for their applicability to press-braked S960 UHSS angle section columns, based on the obtained test and numerical data. The evaluation results revealed that the European code yields unduly conservative and scattered compression resistance predictions when applied to press-braked S960 UHSS angle section columns, while the Australian/New Zealand standard and North American specification lead to a higher degree of design accuracy and consistency, on average, when used for press-braked S960 UHSS angle section columns, though some of the compression resistance predictions are unsafe for those failing by flexural buckling in the 'C' orientation. [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]

• Pin-ended tests on circular high strength concrete-filled stainless steel tube (HCFSST) columns were conducted. • The flexural buckling behaviour and resistances of circular HCFSST columns were discussed. • FE models were developed to validate against the test results and then used to conduct parametric studies. • The applicability of the existing design codes to circular HCFSST columns was assessed. The flexural buckling behaviour and resistances of circular high strength concrete-filled stainless steel tube (HCFSST) columns were examined based on experiments and numerical modelling, and reported in the present paper. The experimental programme was conducted on 12 circular HCFSST columns with various member relative slendernesses, and included material tests, initial global geometric imperfection measurements and pin-ended column tests, with their procedures and setups fully described. The experimentally observed results, including the failure loads and modes as well as the load-deformation curves (load-end shortening curves and load-mid-height lateral deflection curves) of the circular HCFSST column specimens and the development of the longitudinal strains of the outer stainless steel tubes, were presented and discussed. The experimental programme was then supplemented by a numerical modelling programme, where finite element models were developed and validated against the test results, and then used for conducting parametric studies to generate further numerical data on circular HCFSST columns over a broad spectrum of cross-section dimensions and member lengths. Owing to the lack of international design codes for stainless steel–high strength concrete composite structures, the relevant codified design rules for circular normal strength concrete-filled carbon steel tube columns failing by flexural buckling, as used in Europe, America and Australia/New Zealand, were assessed for their applicability to circular HCFSST columns, based on the obtained experimental and numerical data. The assessment results indicated that the design rules, as given in the Australian/New Zealand standard and American specification, lead to many unsafe flexural buckling resistance predictions when used for circular HCFSST columns, while the design rules, as adopted in the European code, result in more safe and reliable design resistances for circular HCFSST columns failing by flexural buckling. [ABSTRACT FROM AUTHOR]

• Flexural buckling of S960 UHSS channel section columns was investigated. • Flexural buckling in both the 'C' and 'reverse C' orientations was examined. • Initial imperfection measurements and ten pin-ended column tests were conducted. • FE models were firstly validated and then used to perform parametric studies. • The applicability of the relevant codified design rules was assessed. Grade S960 ultra-high strength steel is receiving increasing attention owing to its excellent strength-to-weight ratio. However, its application in construction engineering is rather limited due to the lack of adequate design rules, as the current established codes in Europe, North America and Australia/New Zealand only cover the design of steel components with material grades up to S700 (or S690). This prompts investigations into different types of S960 UHSS structural components and development of accurate and efficient design rules for them. The present paper focuses on press-braked S960 UHSS channel section columns prone to flexural buckling about the minor principal axes, with their behaviour and resistances thoroughly examined through experiments and numerical modelling. An experimental programme was firstly performed on two non-slender press-braked channel sections, with five column specimens of varying member lengths employed for each cross-section, and included initial global and local geometric imperfection measurements and pin-ended column tests about the minor principal axes. This was followed by a parallel numerical modelling programme, where finite element (FE) models were developed to simulate the experimental results and afterwards adopted to perform a parametric study to generate additional numerical data over a broader spectrum of cross-section dimensions and member lengths. It is worth noting that there were two orientations associated with minor-axis flexural buckling of press-braked S960 UHSS channel section columns, namely 'C' orientation (indicating that columns buckled towards the webs) and 'reverse C' orientation (indicating that columns buckled towards the flange tips), and both of the two types of failure modes were carefully examined in the present study. It was found that channel section columns failing by flexural buckling in the 'reverse C' orientation generally exhibited superior resistances relative to their counterparts with failure in the 'C' orientation. The experimental and numerical data were also used to assess the applicability of the codified provisions for press-braked S700 (or S690) channel section columns failing by flexural buckling about the minor principal axes to the design of their S960 counterparts. The assessment results indicated that (i) the existing European code leads to overall conservative and scattered design flexural buckling resistances, especially for those relatively short and intermediate press-braked S960 UHSS channel section columns with failure in the 'reverse C' orientation, and (ii) the North American specification and Australian/New Zealand standard result in a higher degree of design accuracy and consistency than the European code, but with many over-predicted flexural buckling resistances for press-braked S960 UHSS channel section short and intermediate columns failing in the 'C' orientation. [ABSTRACT FROM AUTHOR]

• Numerical models for CFS built-up columns with spacers were developed. • Detailed nonlinear response of CFS built-up columns was investigated. • Predictions as per current Australian/European CFS standards were inconsistent. • Improved design equations were proposed for better/reliable strength predictions. This paper deals with the numerical investigation aimed to study the axial capacity and the nonlinear deformation response of pin ended cold-formed steel (CFS) built-up columns under monotonic axial loading, applied concentrically. The built-up sections were constructed by adequately spaced channel sections in a back-to-back configuration, connected through webs by means of connecting elements (CFS channels) called spacers. Self-driving screws were used as fasteners to assemble together the lipped channels and spacers. Finite element (FE) models were established and verified against the previously published built-up columns with similar configuration. An extensive parametric study was conducted by varying the key parameters like plate slenderness of the lipped channels, unbraced chord slenderness, and global slenderness in order to investigate their variation on the ultimate compression resistance of these built-up columns. The effective width method was used to determine the design strengths for these built-up columns using the AS/NZ Specifications and European Specification on cold-formed steel structures, which were later compared with the results obtained from the numerical parametric study. This study indicated that the provisions that are given in the current AS/NZS and European Specification in predicting the strengths of the built-up column with spacers had shortcomings. Therefore, new design equations for the reliable design strength predictions of the CFS built-up column composed of lipped channels with spacers were proposed. The incorporation of spacers curtailed the local buckling half-wave length, which improved the buckling resistance, predominantly in the columns failing by local buckling. [ABSTRACT FROM AUTHOR]