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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 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 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]

• 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]

• 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]