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To study the effect of slenderness ratio on the ultimate bearing capacity of UHPC (ultra-high performance concrete)-encased concrete-filled steel tubular (UC-CFST) columns, a total of nine specimens under axial compression were tested. A finite element model, considering the effects of material nonlinearity and interaction between concrete and steel tube, was developed. A full-range analysis was carried out on the typical load–deformation response of the UC-CFST medium-long columns. The experimental and numerical analysis results showed that with the increase in slenderness ratio, the deformation capacity of the UC-CFST columns increased, the ultimate bearing capacity decreased, and the failure mode changed from exceedance of compressive strength to loss of stability. The internal forces and stress distributions at the mid-height section of the columns at different stages were also investigated. Finally, the applicability of various methods for calculating the ultimate bearing capacity of ordinary concrete-encased CFST (OC-CFST) columns to UC-CFST columns was discussed, including the methods recommended by Chinese standard T/CECS 188-2019, European standard Eurocode 4, Australian/New Zealand joint standard AS/NZS 5100.6 : 2017 and American standard ANSI/AISC 360-16. It was found that the method recommended in AS/NZS 5100.6 : 2017 was suitable for calculating the ultimate bearing capacity of UC-CFST medium-long columns. [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]

ABSTRACT Cold-drawing is one of typical cold-forming techniques in producing stainless steel tubes. Compared with cold-rolling, cold-drawing can be used to manufacture large scale stainless steel tubes. In this study, material properties tests of 14 coupons taken from cold-drawn duplex stainless steel square tubes were reported, along with six stub and seven long column tests under axial compression. Stress-strain curves, ultimate loads and failure characteristics of stub and long columns were obtained. Test results indicate that cold-drawn duplex stainless steel tubes have pronounced cold-forming effect, the yield strength of the flat region reaches up to 750 MPa and the elongation at the fracture decreases significantly. And, all the stub columns show local buckling mode, while most of the long columns undergo overall flexural buckling mode. Finite element models were developed, validated using test data, and then used to generate more results over a wider range of cross-sectional and member slenderness. Both the results of test and numerical modeling were compared with the design strengths of the European, American, Australian/New Zealand and Chinese codes, the design method proposed by Afshan, and the deformation based continuous strength method (CSM). Comparisons show that: for stub columns, design strengths according to all the design codes are underestimated, while the continuous strength method provides reasonable predictions especially for both the stocky and slender cross-sections; for long columns, design strengths calculated using the European, Australian/New Zealand, Chinese codes and the method proposed by Afshan are conservative, while those calculated using the American code are unsafe. Highlights • Cold-drawn process apparently changes the material properties in square tubes. • CSM method gives good predictions for stub columns of cold-drawn square tube. • European and Chinese codes can be used to design long columns of cold-drawn square tube. [ABSTRACT FROM AUTHOR]

Abstract Cold-drawing is one of the typical cold-forming techniques in producing stainless steel circular hollow sections (CHS). Compared with cold-rolling, cold-drawing can produce large scale stainless steel tubes which have wide applications in highly corrosive environment. Nevertheless, few researches have been carried out on the duplex stainless steel CHS columns. In this paper, cold-drawn duplex S22053 stainless steel CHS of three types of cross-sections were tested, including 8 material tensile coupon tests, 6 axially compressed stub column tests and 7 axially compressed long column tests. The material stress-strain curves of the cold-drawn CHS tubes, ultimate loads and failure modes of the stub and long columns were obtained. It has been revealed that material properties of cold-drawn stainless steel CHS tubes are close to those of the virgin plate in the annealed state. Moreover, all the stub columns show local buckling in "elephant foot" mode, while all the long columns undergo overall flexural buckling, among which a long column specimen with the nominal length of 700 mm（CHS-700） shows local buckling after the peak load due to the interaction of axial compression and second-order bending moment. Furthermore, comparing the test values with the predicted values based on the European, American, Australian/New Zealand and Chinese design codes, and the calculation methods available in literatures, it is concluded that the predicted values of the stub columns and the long columns with relatively large member slenderness are all lower than the test values, while the predicted values using the design methods except that in the Chinese design code are higher than the test values for the long columns with relatively small member slenderness. Chinese design code could provide safety predictions for cold-drawn duplex stainless steel CHS columns. Highlights • Behaviors of cold-drawn duplex stainless steel CHS columns were shown through tests. • Comparisons of test results and predictions of current design method were conducted. • CSM and Chinese Code can be used to design stub and long CHS columns respectively. [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]

Recently developed novel high-strength sorbite stainless steel (S600E) integrates the merits of exceptional mechanical properties, high corrosion resistance, effortless weldability, and cost-effectiveness, offering remarkable competitiveness in stainless steel structures. However, the lack of information regarding its mechanical performance impedes its application as a structural component in the construction industry. In this paper, material tensile tests, axial compression stub column tests, and axial compression long column tests were conducted to determine the constitutive curves, failure patterns, and ultimate capacity of cold-formed S600E high-strength stainless steel with a circular hollow section (CHS). The experimental results demonstrate that the material strength of S600E increases to a yield and ultimate strength of 580 MPa and 690 MPa, respectively. In addition, all stub columns are in a local buckling mode, with an "elephant foot" shape at one end, whereas all long columns fail by the overall buckling. To find an accurate ultimate capacity prediction method for the studied columns, the experimental data were compared with those of existing standards and methods. The comparisons demonstrate that (1) for stub columns, all the existing approaches evaluate the axial resistance conservatively, where the continuous strength method (CSM) delivers comparatively precise predictions; and (2) for long columns, the design strength recommended by Australian/New Zealand codes proves to be unsafe. Conversely, the direct strength method (DSM) holds an overly cautious attitude. Among the codes, the Chinese code accurately assesses axial resistance. The findings of this study inform mechanical behaviors for designers and engineers to facilitate the use of high-strength sorbite stainless steel. • Compressive behaviors of novel sorbite stainless steel tubes were assessed. • The applicability of main design methods for strength prediction was estimated. • Current design methods underestimating its strength properties were evaluated. • Chinese code is available for designing such circular hollow section long tubes. [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 extensive experimental investigation of the circular recycled aggregate concrete filled steel tubes (RACFST) stub columns under to axial compression to assess their cross-section behaviour. Recycled aggregate concrete is a sustainable concrete produced with recycled coarse aggregate (RAC) from demolition wastes generally used to fabricate non-structural elements. When compared with natural coarse aggregate (NCA), the recycled coarse aggregate presents lower mechanical properties due to physical and chemical changes that occurred during the recycling process, and thus the resulting RAC possess lower strength than the conventional natural aggregate concrete. However, the confinement provided by the circular steel tube can increase the strength and ductility of RAC in recycled aggregate concrete filled steel tubes (RACFST) columns. The test programme presented in this paper comprised twenty-three composite columns with replacement ratios (the mass percentages of the NCA replaced by RCA in concrete) corresponding to 0% (nature coarse aggregate), 30 and 50% (recycled aggregate concrete), plus four steel columns used for comparison. The experiments have shown that, as anticipated, the concrete core enhances the composite section load-carrying capacity. However, the control over the contents of this concrete core influences the composite section's ductility. If the fill material presents a brittle behaviour, stress redistributions occur in both steel and concrete to compensate for this effect. Since the behaviour of natural aggregate concrete filled steel tubes (NACFST) and RACFST columns are similar, the present paper starts from a study based on a comparative assessment of the recommendations presented in ABNT NBR 8800, ABNT NBR 16239, AISC 360–16, Eurocode 4 and Australian/New Zealand AS/NZS 2327 design standards. These design recommendations proved to be consistent and in line with the performed experiments. Additionally, the results indicated that the cross-section slenderness ratio (D/t) and the confinement ratio directly influence the composite section response. [Display omitted] • An experimental programme was carried out comprising recycled aggregate concrete-filled steel tubular (RACFST) columns. • Different replacement ratios of the nature coarse aggregate replaced by recycled aggregate concrete were assessed. • The steel tubes were produced using a high-frequency induction welding process minimizing the residual stress effects. • The RACFST stub columns presented similar resistances with NACFST stub columns due to confinement contribution. • EC4 and AS/NZS 2327 predictions provide a good approach to be used to RACFST stub columns' design. • NBR 8800 and AISC 360-16 presented very conservative predictions for the columns' strength. [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 a comprehensive experimental and numerical study of the flexural buckling behaviour and resistances of circular recycled aggregate concrete-filled stainless steel tube columns. The experimental programme, adopting four series of column specimens designed with various stainless steel tube sizes, recycled coarse aggregate replacement ratios and member lengths, included material tests on both recycled aggregate concretes and stainless steel tubes, initial global geometric imperfection measurements and pin-ended column tests. The obtained experimental results, including the failure loads, load–mid-height lateral deflection curves and flexural buckling failure modes, were reported in detail. The effects of the stainless steel tube size, recycled coarse aggregate replacement ratio and member length on the flexural buckling resistances of the column specimens were examined. The lateral deflection distributions along the column specimen lengths and the development of the longitudinal strains of the outer stainless steel tubes were discussed. The experimental programme was supplemented by a numerical modelling programme, in which finite element models were developed and validated against the test results and then used for conducting parametric studies to generate further numerical data over a wide range of cross-section dimensions and member lengths. Given that there have been no existing design codes for recycled aggregate concrete–stainless steel composite structures, the relevant codified design rules for circular natural aggregate concrete-filled carbon steel tube columns failing by flexural buckling, as used in Europe, Australia/New Zealand and America, were assessed for their applicability to circular recycled aggregate concrete-filled stainless steel tube columns, based on the test and numerical data. The assessment results revealed that the design rules, as given in the Australian/New Zealand standard and American specification, result in unsafe flexural buckling resistance predictions when used for circular recycled aggregate concrete-filled stainless steel tube columns, while the Eurocode design rules lead to more safe and accurate flexural buckling resistance predictions. Unlabelled Image • Recycled aggregate concrete-filled stainless steel tube (RACFSST) column system has been proposed. • Tests on circular RACFSST columns susceptible to flexural buckling have been conducted. • The flexural buckling behaviour and resistances of circular RACFSST columns have been studied. • FE models have been developed to validate against the test results and then used to conduct parametric studies. • The applicability of the existing design codes to circular RACFSST columns has been evaluated. [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]