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• The flexural buckling behavior of square RACFSST columns after exposure to fire is investigated. • Post-fire pin-ended column tests on twelve square RACFSST column specimens are conducted. • The influences of heating durations and RCA replacement ratios are analysed. • Thermal and mechanical FE models are validated against test results and then used to conduct parametric studies. • The relevant design codes are assessed against the test and FE data. The flexural buckling behaviour and residual resistances of square recycled aggregate concrete-filled stainless steel tube (RACFSST) columns after exposure to fire are studied in this paper, based on experiments and numerical modelling. Twelve column specimens, fabricated from concretes with three recycled coarse aggregate replacement ratios (0%, 35% and 70%), were tested after exposure to the ISO 834 standard fire for 0 min (i.e. at ambient temperature), 15 min, 30 min and 45 min. The experimental investigation included heating of specimens, cylinder tests as well as post-fire initial global geometric imperfection measurements, tensile coupon tests and pin-ended column tests. The test setups, procedures and results were fully reported and the ductility indices, lateral deflection distributions and longitudinal strains were discussed and analysed. A numerical investigation was afterwards carried out, where the test results were used to validate thermal and mechanical finite element models; upon validation, parametric studies were conducted to expand the test data bank over a wider range of cross-section dimensions and member lengths. On the basis of the test and numerical data, the relevant design rules for square natural aggregate concrete-filled carbon steel tube columns at ambient temperature, as set out in the European code, Australian/New Zealand standard and American specification, were assessed, using post-fire material properties, for their applicability to square RACFSST columns after exposure to fire. It was found from the assessment results that the three design codes resulted in overall accurate and consistent post-fire flexural buckling resistance predictions but some were unsafe. [ABSTRACT FROM AUTHOR]

• The compressive behaviour of square RACFSST stub columns after exposure to fire is investigated. • Twelve post-fire compression tests are conducted. • The influences of heating durations and RCA replacement ratios are discussed. • Thermal and mechanical FE models are validated against test results and then used to conduct parametric studies. • The relevant design codes are assessed against the test and FE data. Experimental and numerical studies on the cross-section compressive behaviour and residual resistances of square recycled aggregate concrete-filled stainless steel tube (RACFSST) stub columns after exposure to fire are reported in this paper. An experimental programme was firstly carried out on twelve stub column specimens with three recycled coarse aggregate replacement ratios (0%, 35% and 70%) after exposure to the ISO-834 standard fire for 0 min (i.e. at ambient temperature), 15 min, 30 min and 45 min. The test results, including load–end shortening curves, failure loads and failure modes, were presented, with the initial compressive stiffness and confinement effect analysed. The experimental programme was followed by a numerical modelling programme, where thermal and mechanical finite element models were developed and validated against the test results and afterwards used to conduct parametric studies to generate additional numerical data over a wide range of cross-section dimensions. Based on the test and numerical data, the relevant design rules for square natural aggregate concrete-filled carbon steel tube stub columns at ambient temperature, as specified in the European code, Australia/New Zealand standard and American specification, were evaluated, using post-fire material properties, for their applicability to square RACFSST stub columns after exposure to fire. The evaluation results generally revealed that the European code and Australian/New Zealand standard led to a good level of design accuracy, while the American specification resulted in slightly conservative post-fire cross-section compression resistance predictions. [ABSTRACT FROM AUTHOR]

This paper presents experimental and numerical investigations into the post-fire cross-section compressive behaviour and resistances of circular recycled aggregate concrete-filled stainless steel tube (RACFSST) stub columns. Twelve stub column specimens, fabricated from concretes with three recycled coarse aggregate replacement ratios (0%, 35% and 70%), were tested after exposure to the ISO-834 standard fire for 0 min (i.e. at ambient temperature), 15 min, 30 min and 45 min. The experimental investigation included heating and cooling of specimens, cylinder tests and post-fire tensile coupon tests and stub column tests. The test results, including load–end shortening curves, failure loads and failure modes, were fully reported and the initial compressive stiffnesses and confinement effect were discussed. The numerical investigation was subsequently conducted, where thermal and mechanical finite element models were developed and validated against the test results and then used to perform parametric studies to generate further numerical data. Given the absence of design codes for stainless steel–recycled aggregate concrete composite structures after exposure to fire, the relevant design rules for circular natural aggregate concrete-filled carbon steel tube stub columns at ambient temperature, as set out in the European code, Australia/New Zealand standard and American specification, were assessed, using post-fire material properties, for their applicability to circular RACFSST stub columns after exposure to fire, based on the test and numerical data. The assessment results generally revealed that the European code and the Australian/New Zealand standard led to an acceptable level of design accuracy and consistency, while the American specification resulted in rather conservative and scattered post-fire cross-section compression resistance predictions. • The compressive behaviour of circular RACFSST stub columns after exposure to fire is investigated. • Post-fire compression tests on twelve circular RACFSST stub column specimens are conducted. • The influences of heating durations and RCA replacement ratios are analysed. • Thermal and mechanical FE models are validated against test results and then used to conduct parametric studies. • The relevant design codes are assessed against the test and FE data. [ABSTRACT FROM AUTHOR]

This paper reports experimental and numerical investigations into the structural behaviour and resistances of high strength concrete-filled stainless steel tube (HCFSST) beam-columns under combined compression and bending. An experimental investigation was conducted on sixteen HCFSST beam-columns specimens fabricated from stainless steel tubes with two cross-section sizes and high strength concretes with four material grades, and included concrete cylinder tests, tensile coupon tests, initial global geometric imperfection measurements and eccentric compression tests. The test setups and procedures were fully reported and the experimental observations were discussed and analysed in detail. It was found that the plane cross-section assumption was valid for eccentrically loaded HCFSST sections and the lateral deflection distribution patterns for HCFSST beam-columns were approximately half-sine wave shapes. The test results were used in a subsequent numerical investigation for the validation of finite element models, which were then employed to conduct parametric studies to generate additional numerical data over a wide range of cross-section dimensions, member lengths and loading combinations. Based on the experimental and numerical results, the relevant design rules, as set out in the European code, American specification and Australian/New Zealand standard, were evaluated for their applicability to HCFSST beam-columns. The evaluation results revealed that the European code provided accurate but scattered failure load predictions when used for HCFSST beam-columns, while the American specification and Australian/New Zealand standard resulted in conservative and scattered failure load predictions. • The behaviour of high strength concrete-filled stainless steel tube (HCFSST) beam-columns is investigated. • Eccentric compression tests on sixteen HCFSST beam-column specimens are conducted. • The ductility, strength, longitudinal strain development and lateral deflection distribution are analysed. • FE models are developed to validate against the test results and then used to conduct parametric studies. • The applicability of relevant design codes is assessed against test and FE data. [ABSTRACT FROM AUTHOR]

The present paper reports experimental and numerical studies on the flexural buckling behaviour and resistances of laser-welded stainless steel T-section columns. An experimental programme, including initial global and local geometric imperfection measurements and ten fixed-ended column tests, was firstly performed. The test results, including failure loads, load–mid-height lateral deflection curves and two types of failure modes ('C'-shaped and 'reverse C'-shaped flexural buckling), were reported in detail. Following the experimental programme, a numerical modelling programme was carried out, where finite element models were 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 and member lengths. On the basis of the test and numerical results, the relevant design buckling curves, as given in the European code and American specification, were evaluated. The evaluation results revealed that both codified design buckling curves generally resulted in accurate and consistent flexural buckling resistance predictions for laser-welded stainless steel T-section columns. • The minor-axis flexural buckling behaviour of laser-welded stainless steel T-section columns is investigated. • Ten fixed-ended column tests are conducted. • FE models are developed and validated against the test results and then used to conduct parametric studies. • The codified design buckling curves are evaluated and shown to result in accurate failure load predictions. [ABSTRACT FROM AUTHOR]

This paper presents experimental and numerical studies of the local buckling behaviour and compression resistances of cold-formed S700 high strength steel circular hollow sections (CHS) after exposure to elevated temperatures. The testing programme included post-fire material tests, initial local geometric imperfection measurements and stub column tests on ten specimens. Then, finite element models were developed to simulate the test structural responses and employed to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions. Given that there are no existing design standards for high strength steel structures after exposure to elevated temperatures, the relevant ambient temperature design rules were evaluated, using post-fire material properties, for their applicability to cold-formed S700 high strength steel CHS after exposure to elevated temperatures, based on the test and numerical data. The evaluation results revealed that (i) the codified slenderness limits were generally accurate when used for cross-section classification of post-fire cold-formed S700 high strength steel CHS and (ii) although the codified design rules resulted in overall relatively accurate cross-section compression resistance predictions, the predicted resistances were conservative for cold-formed S700 high strength steel non-slender CHS after exposure to elevated temperatures of 900 °C and 1100 °C (owing to the high levels of material strain hardening) and those slender CHS (owing to the conservatism of the codified effective width methods). • Stub column tests on S700 high strength steel CHS after exposure to elevated temperatures were conducted. • Their post-fire local buckling behaviour and compression resistances were investigated. • FE models were developed to simulate the test results and then used to conduct parametric studies. • The applicability of the relevant ambient temperature design rules was evaluated. [ABSTRACT FROM AUTHOR]

A testing and numerical modelling programme has been conducted to investigate the flexural buckling behaviour and resistance of press-braked S690 high strength steel angle section long columns. The testing programme adopted two press-braked S690 high strength steel equal-leg angle sections and included initial geometric imperfection measurements as well as twelve pin-ended column tests. The testing programme was accompanied by a 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 used to generate further numerical data over a wide range of cross-section dimensions and member effective lengths. The obtained test and numerical data were used to evaluate the existing design rules for press-braked S690 high strength steel angle section long columns, as specified in the North American specification, Australian/New Zealand standard and European code. The evaluation results revealed that the North American specification and Australian/New Zealand standard result in a high level of design accuracy and consistency, while the Eurocode leads to excessively conservative and scattered failure load predictions. Finally, a new design approach was proposed and shown to offer more accurate and consistent failure load predictions, with less calculation works, than the design codes. • The structural behaviour of press-braked S690 high strength steel angle section long columns was studied. • Twelve pin-ended column tests were conducted. • FE models were developed and validated against the test results and then used to perform parametric studies. • The accuracy of the codified design rules was evaluated based on the test and FE data. • A new design approach was proposed and shown to result in a higher degree of design accuracy, consistency and efficiency. [ABSTRACT FROM AUTHOR]

The present paper reports experimental and numerical investigations into the post-fire local buckling behaviour and residual resistances of S700 high strength steel circular hollow sections (CHS) under combined compression and bending. A testing programme was firstly conducted and included heating and cooling of specimens as well as post-fire material tensile coupon tests and eccentrically loaded stub column tests. Following the testing programme, a numerical modelling programme was carried out, where finite element models were developed to replicate the test results and then employed to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions and loading combinations. Due to the absence of design standards for high strength steel structures after exposure to fire, the codified ambient temperature design interaction curves for high strength steel CHS under combined compression and bending were assessed, using post-fire material properties, for their applicability to post-fire S700 high strength steel CHS. The assessment results revealed that the design interaction curves in the European code and American specification yield a satisfactory level of accuracy and consistency when used for post-fire S700 high strength steel CHS, while the design interaction curves in the Australian standard provide slightly conservative residual resistance predictions. • The post-fire behaviour of S700 high strength steel CHS stub columns under combined loading is investigated. • Ten post-fire eccentric compression tests are conducted. • FE models are developed to validate against the test results and then used to conduct parametric studies. • The applicability of the relevant ambient temperature design rules is evaluated. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical study of eccentrically loaded circular recycled aggregate concrete-filled stainless steel tube (RACFSST) stub columns. The testing programme was conducted on twelve specimens designed with different stainless steel tube section sizes and recycled coarse aggregate replacement ratios, and included tensile coupon tests, concrete cylinder tests and eccentric compression tests. The test results, including the failure loads and modes, load–mid-height lateral deflection curves and evolution of neutral axis, were reported and discussed. Following the testing programme, a numerical modelling programme was conducted, with finite element models developed and validated against the test results and then employed to perform parametric studies to generate further numerical data. The confinement effects were analysed based on the numerical data. The relevant design interaction curves, as set out in the European code, American specification and Australian/New Zealand standard, were assessed for their applicability to circular RACFSST stub columns under combined compression and bending. On the basis of the quantitative and graphical assessments, it has been found that (i) each set of codified design interaction curve leads to similar assessment results for eccentrically loaded circular RACFSST stub columns with different recycled coarse aggregate replacement ratios and (ii) the failure load predictions from the codified design interaction curves are conservative. • The structural behaviour and resistance of circular RACFSST stub columns under combined loading are investigated. • Twelve eccentric compression tests are conducted. • FE models are developed to validate against the test results and then used to conduct parametric studies. • The confinement effects of different types of RACFSST composite sections are discussed. • The applicability of the relevant codified N–M interaction curves is evaluated. [ABSTRACT FROM AUTHOR]

A new high-chromium grade EN 1.4420 stainless steel, which possesses higher material strength and better corrosion resistance but lower material price than the currently most commonly used grade EN 1.4301 stainless steel, has been recently developed, with a good potential in engineering practice. The present paper reports experimental and numerical investigations into the structural behaviour and resistance of concrete-filled high-chromium stainless steel tube (CFHSST) stub columns under combined compression and bending. The experimental investigation was conducted on twelve CFHSST stub column specimens fabricated from high-chromium grade EN 1.4420 stainless steel tubes with three cross-section sizes and concretes with two grades. The failure loads, mid-height lateral deflections, evolution of neutral axis and confinement effect were analysed and discussed. Numerical modelling was subsequently carried out, where finite element models were developed to simulate the test results and then employed to conduct parametric studies to generate further numerical data. The relevant design interaction curves, as set out in the European code, American specification and Australian/New Zealand standard, were assessed for their applicability to CFHSST stub columns under combined compression and bending, based on test and numerical data. The assessment results revealed that the European code and Australian/New Zealand standard provide overall accurate failure load predictions, while the American specification underestimates the failure loads for CFHSST stub columns under combined compression and bending, due to the conservative shape of the design interaction curve. • The structural behaviour of CFHSST stub columns under combined compression and bending is studied. • Twelve eccentric compression tests on CFHSST stub columns are conducted. • The test results, including the neutral axis and the confinement effect, are discussed. • FE models are developed to validate against the test results and then used to conduct parametric studies. • The relevant codied design interaction curves are assessed against the test and FE data. [ABSTRACT FROM AUTHOR]

• The structural behavior and capacity of RACFSST stub columns under combined loading are studied. • Twelve eccentric compression tests on RACFSST stub columns are conducted. • The evolution of neutral axis in RACFSST composite section as well as the confinement effect are discussed. • FE models are developed to validate against the test results and then used to conduct parametric studies. • The relevant design codes are assessed against the test and FE data. This paper reports experimental and numerical investigations into the behaviour and resistance of recycled aggregate concrete-filled stainless steel tube stub columns under combined compression and bending. Eccentric compression tests were conducted on twelve stub column specimens fabricated from austenitic stainless steel tubes with two cross-section sizes and concretes with three recycled coarse aggregate replacement ratios (0%, 35% and 70%). The test results, including the failure loads, load–mid-height lateral deflection curves, evolution of neutral axis and confinement effect, were discussed in detail. The testing programme was followed by a numerical modelling programme, where finite element models were 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 and loading combinations. Given that there are no existing design codes for recycled aggregate concrete–stainless steel composite structures, the relevant codified design rules for natural aggregate concrete filled-carbon steel tube stub columns under combined compression and bending, as set out in the European code, American specification and Australian/New Zealand standard, were evaluated for their applicability to recycled aggregate concrete filled-stainless steel tube stub columns, based on the test and numerical data. The evaluation results revealed that the European code and Australian/New Zealand standard generally provide an acceptable level of design accuracy, while the American specification yields unduly conservative failure load predictions. [ABSTRACT FROM AUTHOR]

This paper reports experimental and numerical investigations into the structural behaviour and residual capacity of concrete-filled high strength steel tube (CFHST) stub columns after exposure to fire. The experimental investigation was conducted on twelve square CFHST stub column specimens after exposure to the ISO-834 standard fire for 15 min, 30 min and 45 min and four reference specimens at ambient temperature. The test results, including failure loads, load–end shortening curves, initial compressive stiffnesses and failure modes, were fully reported and discussed. A numerical investigation was subsequently conducted, where thermal and mechanical finite element models were developed and validated against the test results, and afterwards used to performed parametric studies to generate further numerical data over a wide range of cross-section dimensions. Owing to the absence of design codes for composite structures after exposure to fire, the relevant ambient temperature design rules, as set out in European code, American specification and Australian/New Zealand standard, were evaluated, using post-fire material properties, for their applicability to post-fire CFHST stub columns, based on the test and numerical data. The evaluation results revealed that all the three design codes generally yield accurate failure load predictions for CFHST stub columns after exposure to fire. • Post-fire tests on concrete-filled high strength steel tube (CFHST) stub columns were conducted. • The behaviour and residual resistance of CFHST stub columns after exposure to fire were analysed. • FE models were validated against the test results and then used to conduct parametric studies. • The applicability of the ambient temperature design codes to post-fire CFHST stub columns was demonstrated. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical investigation into the post-fire behaviour and residual capacity of S700 high strength steel circular hollow section (CHS) beam–columns. The experimental investigation was performed on ten S700 high strength steel CHS beam–columns and included heating and cooling of the specimens as well as post-fire material testing, initial global geometric imperfection measurements and pin-ended eccentric compression tests. A subsequent numerical investigation was conducted, where finite element models were developed and validated against the test results and then employed to carry out parametric studies to generate further numerical data over a wide range of cross-section dimensions, member lengths and loading combinations. In view of the fact that there are no specific provisions for the design of steel structures after exposure to fire, the relevant room temperature design interaction curves were evaluated, using post-fire material properties, to assess their applicability to S700 high strength steel CHS beam–columns after exposure to fire, based on the test and numerical data. The evaluation results revealed that the interaction curves provided in the American Specification and Australian Standard result in a high level of design accuracy and consistency, while the Eurocode interaction curve leads to more conservative and scattered failure load predictions. Finally, a revised Eurocode interaction curve, with more accurate end points, was proposed and shown to offer improved failure load predictions for S700 high strength steel CHS beam–columns after exposure to fire. • Tests on ten S700 high strength steel CHS beam–columns after exposure to fire are conducted. • The post-fire member behaviour and residual capacity are studied. • FE models are developed to validate against the test results and then used to conduct parametric studies. • The applicability of the ambient temperature codified design interaction curves is assessed. • A revised Eurocode design interactive curve is proposed. [ABSTRACT FROM AUTHOR]

This paper reports an experimental and numerical investigation into the cross-section behaviour and resistances of press-braked stainless steel channel sections under combined compression and major-axis bending moment. A testing programme was firstly conducted, including initial local geometric imperfection measurements and major-axis eccentric compression tests on ten press-braked stainless steel channel section stub column specimens. Following the testing programme, a numerical modelling programme was performed, where finite element models were developed and validated against the test results and then adopted to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions and initial loading eccentricities. Based on the obtained test and numerical data, the existing design interaction curves, as given in the European code, American specification and Australian/New Zealand standard, were assessed and shown to result in conservative cross-section resistance predictions for press-braked stainless steel channel sections under major-axis combined loading. The conservatism of the codified design interaction curves stems from the conservative end points (i.e. cross-section resistances under pure compression and pure bending), which are determined without considering the effect of material strain hardening, and the inefficient linear shape, which ignores the effect of stress redistribution. Improved design interaction curves were proposed through the adoption of (i) more accurate end points, which are calculated with a rational exploitation of material strain hardening by continuous strength method and (ii) more efficient nonlinear shape, which allows for the stress redistribution. The proposed design interaction curves were shown to result in substantially more accurate resistance predictions for press-braked stainless steel channel sections under major-axis combined loading than their codified counterparts. The reliability of the proposed design interaction curves was confirmed by means of statistical analyses. [Display omitted] • Press-braked stainless steel channel sections under combined loading were studied. • Ten major-axis eccentric compression tests were conducted. • FE models were developed and validated and then used to perform parametric studies. • The codified design interaction curves were assessed, revealing conservatism. • New design interaction curves were proposed and shown to yield higher accuracy. [ABSTRACT FROM AUTHOR]

This paper reports experimental and numerical studies on the post-fire behaviour and residual resistances of S700 high strength steel tubular section stub columns under combined compression and bending. A testing programme was firstly performed, including heating and cooling of specimens as well as post-fire material testing, initial local geometric imperfection measurements and eccentric compression tests. The testing programme was followed by a numerical modelling programme, where finite element models were developed and validated against the test results and then employed to carry out parametric studies to generate further numerical data over a wide range of cross-section dimensions and loading combinations. Given that there are no design standards for high strength steel structures after exposure to fire, the design interaction curves for high strength steel tubular section stub columns under combined loading at ambient temperature, as given in the European code, American specification and Australian standard, were evaluated, using post-fire material properties, for their applicability to S700 high strength steel tubular section stub columns under combined loading after exposure to fire. The evaluation results revealed that all the three sets of codified design interaction curves yield overall accurate post-fire residual resistance predictions for S700 high strength steel tubular section stub columns under combined loading, with the highest level of design accuracy offered by the American specification. • The post-fire behaviour S700 HSS tubular section stub columns under combined loading is investigated. • Ten post-fire eccentric compression tests were conduced. • FE models were developed to validate against the test results and then used to conduct parametric studies. • The applicability of the relevant ambient temperature design rules was assessed. [ABSTRACT FROM AUTHOR]

This paper presents an in-depth experimental and numerical investigation into the behaviour and resistances of press-braked stainless steel channel sections under combined compression and bending moment about the minor principal axis. The experimental programme adopted two press-braked stainless steel channel sections and included initial local geometric imperfection measurements and ten eccentrically loaded stub column tests. The loading eccentricity was varied to achieve a range of ratios of compression load to minor-axis bending moment. Two types of failure mode, namely 'C'-orientation failure (indicating that failure specimens bent towards the web) and 'reverse C'-orientation failure (signifying that failure specimens bent towards the flange tips), were observed upon testing. The experimental 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 over a wide range of cross-section dimensions and initial loading eccentricities. The obtained test and numerical data were then adopted to assess the accuracy of the current codified design rules for press-braked stainless steel channel sections under combined compression and minor-axis bending, as given in the European code, American specification and Australian/New Zealand standard. The assessment results revealed that the codified design rules yield excessively conservative and scattered resistance predictions, owing to the neglect of the favourable material strain hardening of stainless steel and the beneficial stress redistribution within channel sections under combined loading. Improved design rules featuring more efficient interaction curves, anchored to more accurate end points (i.e. cross-section resistances under pure compression and pure bending), were then proposed. The new design proposals were shown to yield more accurate and consistent resistance predictions over the existing design rules. Statistical analyses were also conducted to confirm the reliability of the new design proposals. • The behaviour of press-braked stainless steel channel sections under minor-axis combined loading was studied. • Ten eccentrically loaded stub column tests were carried out about the minor principal axis. • FE models were developed and validated against the test results and then used to conduct parametric studies. • The codified design interaction curves were assessed based on the test and FE data, indicating inaccuracy. • New design interaction curves were proposed and shown to substantially improve the resistance predictions. [ABSTRACT FROM AUTHOR]

• Eccentric compression tests on high strength concrete-filled high strength steel tube (HCFHST) stub columns were conducted. • The structural behaviour and resistances of HCFHST stub columns under combined loading were studied. • The eccentric compression test results for HCFHST stub 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 HCFHST stub columns under combined loading was evaluated. This paper presents comprehensive experimental and numerical investigations into the structural behaviour and resistances of high strength concrete-filled high strength steel tube (HCFHST) stub columns under combined compression and bending. The combined loading tests were conducted on twelve stub column specimens fabricated from S700 high strength steel square hollow section tubes with two cross-section dimensions and concretes with three grades (C40, C80 and C110). The combined loading test setup, procedures and results, including the failure loads, load–mid-height lateral deflection curves and failure modes, were reported in detail. The failure loads and the evolution of the neutral axis of the HCFHST stub column specimens under combined loading were analysed. The development and distribution of the transverse and longitudinal strains of the outer S700 high strength steel tubes were discussed. The experimental programme was followed by a numerical modelling programme, where finite element models were initially developed and validated against the test results and then used to conduct parametric studies to generate further numerical data. The test and numerical data were used to evaluate the applicability of the relevant design rules, as set out in the European code, American specification and Australian/New Zealand standard, to HCFHST stub columns under combined loading. The evaluation results generally indicated that the European code and Australian/New Zealand standard slightly overestimate the failure loads for HCFHST stub columns under combined loading, while the American specification offers accurate, consistent and safe failure load predictions when applied to eccentrically loaded HCFHST stub columns. [ABSTRACT FROM AUTHOR]

This paper reports comprehensive experimental and numerical investigations into the cross-sectional behaviour and residual resistances of S700 high strength steel square and rectangular hollow section stub columns after exposure to elevated temperatures. The experimental investigation employed three cold-formed S700 high strength steel square and rectangular hollow sections, and for each cross-section, five geometrically identical stub column specimens were prepared and tested after exposure to different levels of elevated temperature, namely 30 °C, 400 °C, 600 °C, 800 °C and 1000 °C. This was followed by a numerical investigation, where finite element models were initially developed and validated against the experimental results and then adopted to conduct parametric studies to generate further numerical data over a wide range of cross-section dimensions. Owing to the absence of design standards for high strength steel structures after exposure to elevated temperatures, the corresponding ambient temperature design rules, as provided in the European code, American specification and Australian standard, were evaluated for their applicability to S700 high strength steel square and rectangular hollow section stub columns after exposure to elevated temperatures. The evaluation results indicated that the ambient temperature slenderness limits for internal plate elements in compression, as specified in the three considered design standards, are accurate and safe when used for cross-section classification of S700 high strength steel square and rectangular hollow section stub columns after exposure to elevated temperatures. In terms of the cross-section compression resistance predictions, the Australian standard was shown to provide accurate, consistent and safe predicted resistances for S700 high strength steel square and rectangular hollow section stub columns after exposure to different levels of elevated temperature. The European code and American specification were found to yield accurate, consistent and safe post-fire compression resistance predictions for S700 high strength steel non-slender square and rectangular hollow section stub columns but over-predict the post-fire compression resistances for those slender section stub columns, owing principally to the employment of unsafe effective width expressions. • The post-fire cross-sectional behaviour and resistances of S700 HSS SHS and RHS stub columns were studied. • Post-fire compression tests on 15 S700 HSS SHS and RHS stub columns were conducted. • FE models were developed to validate against the test results and then used to conduct parametric studies. • The applicability of the relevant ambient temperature codified design rules was assessed. [ABSTRACT FROM AUTHOR]

• The bearing–curling interaction of austenitic stainless steel thin sheet bolted connections was studied. • Tension tests were conducted on 26 austenitic stainless steel thin sheet bolted connection specimens. • FE models were developed and validated against test results and then adopted to conduct parametric studies. • The effects of end and edge distances, longitudinal and transverse spacings and thickness were discussed. • Design analyses were conducted. The bearing–curling interactive behaviour and capacities of austenitic stainless steel thin sheet bolted connections are studied in this paper, underpinned by testing and numerical modelling. Experiments were firstly conducted on 26 austenitic stainless steel thin sheet bolted connection specimens, including 19 specimens designed with curling and 7 specimens designed without curling. The test failure loads, failure modes, load–in-plane elongation curves and load–out-of-plane deformation curves were fully reported. The experimental programme was followed by a numerical modelling programme, where finite element models were firstly developed to repeat the experimental results and then used to carry out parametric studies to generate a numerical data pool. Based on the obtained numerical data, the influences of end distance, edge distance, longitudinal spacing, transverse spacing and sheet thickness on failure loads of austenitic stainless steel thin sheet bolted connections were discussed. The test and numerical data were used to assess the existing design provisions, as given in the European code and American specification. The assessment results revealed that the European code led to overall accurate but scattered failure load predictions, while the American specification was shown to result in overly unsafe and scattered failure load predictions. [ABSTRACT FROM AUTHOR]

• A database including 812 datasets of welded I-section beam–columns with various steel grades, geometric dimensions and failure modes was established. • Regression models were developed to predict failure loads of normal and high strength steel I-section beam–columns based on seven machine learning algorithms. • The regression models were evaluated and the XG-trained regression model had the highest level of accuracy. • The unified machine-learning-based design method yielded improved design accuracy than the existing design codes. High strength steel is regarded as a promising construction material due to its superior mechanical properties. However, the codified failure load predictions for high strength steel welded I-section beam–columns are not accurate in some cases owing to the lack of relevant design codes for high strength steel structures. In addition, current design codes ignore the interaction effect of the cross-section plate elements, leading to the inaccuracy of codified predictive ultimate resistances for both normal and high strength steel beam–columns. In this paper, a unified and accurate design method was proposed based on machine learning for both normal and high strength steel welded I-section beam–columns failing by different failure modes. Firstly, a total of 812 experimental and numerical data on welded I-section beam–columns with various steel grades, geometric dimensions, including cross-section dimensions and member lengths, and failure modes, including global buckling, local buckling and local–global interactive buckling were collected to establish a database. Seven machine learning algorithms, including Decision Tree, Random Forest, Support Vector Machine, K-Nearest Neighbour, Adaptive Boosting, Extreme Gradient Boosting and Categorical Boosting were applied to develop regression models to predict failure loads. Based on the established database, each machine learning model was then trained and key hyperparameters were optimised. The model performance was evaluated through a series of statistical indicators and the feature importance analysis, and the evaluated results indicated that the XG-trained regression model had the highest level of accuracy. Finally, the predictions given by the XG-trained regression model were compared with those of the existing codified design provisions, as given in Eurocode and American codes. The evaluation results indicated that the codified predictive bearing capacities of I-section beam–columns were scattered and inaccurate, while the XG-trained regression model provided substantially improved failure load predictions. [ABSTRACT FROM AUTHOR]