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Under coupled bending-shear-torsion (B-S-T) loading combinations, the ultimate bearing capacity of concrete filled steel tube (CFST) short columns has not been studied. In this paper, the test on eight CFST short columns was carried out. The load-deformation relations and failure modes of CFST short columns were obtained and analyzed. Based on experimental results, the failure mechanism of CFST short columns were obviously affected by the ratio of bending moment to torque, and CFST short columns under coupled B-S-T loading combinations had good ductility. The ultimate bending-shear bearing capacity of CFST short columns was significantly decreased by increasing torsion moment. Moreover, nonlinear finite element analysis was performed, which generated an accurate prediction of the ultimate capacity of concrete filled steel tube short columns under coupled B-S-T. As a conclusion, a simplified design equation for calculating the coupled B-S-T bearing capacity of CFST short columns was proposed according the regression results of the finite element parametric analysis. [ABSTRACT FROM AUTHOR]

Based on a quasi-static test on six concrete-filled double skin steel tube columns subject to cyclic pure torsion, the torsion behavior of concrete-filled double skin steel tube columns with various section types, hollow ratios and steel ratios was studied. The failure modes, torsion-rotation angle hysteretic curves and strain distribution law of concrete-filled double skin steel tube columns under reversed cyclic loading are obtained. The test results show that the hysteretic curves of concrete-filled double skin steel tube columns under pure torsion are plump. The unloading stiffness was close to the initial elastic stiffness. The good energy dissipation capacity of concrete-filled double skin steel tube columns can be observed. Under a cyclic torsion moment, the torsion-resistance capacity of circular concrete-filled double skin steel tube columns was better than that of square and rectangular concrete-filled double skin steel tube columns. With the same thickness of the inner steel tube and the same section size and shape, the hollow ratio of concrete-filled double skin steel tube columns has little effect on the cyclic torsion behavior. [ABSTRACT FROM AUTHOR]

Under gravity and the horizontal earthquake load, the eccentric compression and torsion combined action will be produced in the piers of curved girder bridges and the main arch of arch bridge. In order to study the torsion behavior of concrete filled steel tube columns subjected to eccentric compression, tests were carried out on eight specimens of concrete filled steel tube column subjected to static pure torsion, cyclic pure torsion and eccentric compression-torsion cyclic load. The results of tests have indicated that, the hysteresis curve of concrete filled steel tube column subjected to torsion cyclic load was plump; no pinch phenomenon can be found; the damage and degradation degree of the strength and stiffness of specimens is lower; and high energy dissipation capacity can be achieved. The stiffness degradation of the specimens with square section subjected to eccentric compression-torsion cyclic load is more obvious. The eccentric compression has led to weaken of the energy dissipation capacity of the square section concrete filled steel tube column. Under the ultimate state, the wave angle of steel tube was affected by the eccentric compression. [ABSTRACT FROM AUTHOR]

Abstract: When subjected to the horizontal earthquake load, compression–bending–torsion combined actions often exist in the piers of curved bridges because the center of stiffness and the center of mass of curved bridges do not locate at the same position. A new fiber beam-column element considering the nonlinear torsion behavior for concrete filled steel tubes with circular section was developed based on the traditional fiber beam-column model, which had widely been used. The calculation and solution procedures of the proposed fiber beam-column model were also illustrated. The reasonable geometrical relations, material constitutive law and force equilibrium equations were all applied. Based on the principles of fiber beam-column element considering torsion effect, a nonlinear solution program was developed using FORTRAN language. The entire loading history of concrete filled steel tube columns subjected to combined compression–bending–torsion load could be predicted with good agreement with test results. Using the proposed fiber beam-column model for the time-history analysis of curved steel–concrete composite girder bridges, the high solution precision and efficiency could be obtained, compared with the traditional finite element model. [Copyright &y& Elsevier]

Abstract: Concrete filled steel tube (CFST) columns are currently being widely used in the construction of modern buildings and bridges. In practice, the torsion effect will be often created in CFST columns when the horizontal earthquake happened. Based on geometrical, material constitutive and equilibrium equations, a theoretical model called laminated tubes model for analyzing the mechanical behavior of CFST columns under axial force–torsion combined action was proposed. The confined effect provided by the steel tube and the compression softening effect of the concrete could be considered in the proposed concrete material model. Based on the theoretical model, the non-linear analysis program was developed for obtaining the entire loading history of CFST columns under axial force–torsion combined action. The predicted results have good agreement with test results. The torsion behavior of CFST columns was detailed discussed based on the theoretical model, and the simplified formulae for practical design are also proposed based on regression methods. [Copyright &y& Elsevier]

Abstract: Based on the force–displacement mixed control quasi-static test on eight CFST columns subjected to combined compression, bending and torsion cyclic load, the mechanical behavior of CFST columns with various section types, bending moment to torsion moment ratios and axial load levels was studied. The test results showed that the hysteretic curves of CFST columns under combined compression, flexure and torsion are plump due to the good seismic behavior and the ductility was also good. But for rectangular CFST columns with high bending moment to torsion moment ratio, the strength degradation was observed due to the local buckling of the steel plate at the bottom. The torsion capacity of CFST columns would be reduced by the bending moment. The plane section assumption of axial strain of CFST columns could be satisfied. The shear strain of the steel tube has good linear relationship with the rotation angle of the section when CFST columns subjected to combined compression, flexure and torsion. Based on the test results and literatures available, the mechanism of CFST columns was qualitatively analyzed. [Copyright &y& Elsevier]

Recent developments in the high-output wind turbine have heightened the need for CFDST support towers. Tapered Concrete-Filled Double Skin Steel Tubular columns with Large Hollow Ratios (TLHR-CFDSTs) are the typical members in the wind turbine towers, which are usually subjected to torsion during the life cycle. It is necessary to pay more attention to these members under torsion due to their tapered shapes and thin-walled cross sections. This paper thus presents an experimental study on the torsional behaviour of the TLHR-CFDST column. Specimens with different tapered angles, hollow ratios, tubes' thicknesses and axial compression ratios were tested under pure torsion and compression–torsion. The typical failure modes, torque versus deformation relations, strain distributions and the influence of important parameters are revealed. Based on the experimental results, the mechanism of TLHR-CFDST columns under torsion is discussed. The applicability of existing torsional capacity calculation methods is evaluated and finally a simplified method for predicting the torsional capacity of TLHR-CFDST columns is proposed. • Tests on TLHR-CFDST columns under pure torsion and compression–torsion​ are reported. • Behaviour and parametric effects of TLHR-CFDST columns under torsion are revealed. • Torsional mechanism of TLHR-CFDST columns is discussed. • Theoretical method for predicting the torsional capacity of TLHR-CFDST columns is proposed. [ABSTRACT FROM AUTHOR]

This paper presents a pseudo-static test investigation and finite element analysis on the behavior of circular concrete-filled double skin steel tube (CFDST) members under axial compression and torsion. The hollow ratio (χ) and axial compression ratio (n) are considered in the test study. The ductility, hysteretic behavior, failure modes, and compression–torsion correlation of circular CFDST members are discussed. The comparison results show that the validated finite element model is capable to capture the behavior of circular CFDST members under compression and torsion. The effect of loading paths and various parameters on the compression–torsion correlation of circular CFDST members are analyzed. Parametric analyses are carried out to investigate the effect of key parameters, such as material properties, nominal steel ratio, the wall thickness of inner steel tube, and hollow ratio on the compression–torsion correlation of circular CFDST members. It can be seen that the circular CFDST members under compression and torsion possess good load-bearing capacity, energy dissipation, and ductility properties. The loading paths, yield strength of inner and outer steel tubes, nominal steel ratio, and the wall thickness of inner steel tubes have little effect on the compression–torsion correlation of the composite members. When the axial compression ratio is less than 0.2, the axial compression load can slightly improve the torque capacity of circular CFDST members. Finally, the compression–torsion correlation equation of these members was proposed by regression analysis, and design formulas with good accuracy for predicting the torque capacity of circular CFDST members under compression and torsion were proposed. • Test investigation and numerical analysis were conducted to study behavior of CFDST members under compression and torsion. • Parametric analyses and regression analysis were conducted to propose the Axial compression and torsion correlation equation of CFDST members. • Parametric analyses have been conducted considering key parameters. • The axial compression and torsion correlation equation of CFDST members were proposed via regression analysis. • Formulas with good accuracy for predicting the torque capacity of CFDST members under compression and torsion were proposed. [ABSTRACT FROM AUTHOR]

• Seismic performance of H-CFST columns under cyclic torsional and compression–cyclic torsional loads is investigated. • Two types of H-CFST columns under cyclic pure torsion and compression-torsion are tested. • Shear capacity of steel and concrete under combined normal and shear stress conditions is firstly studied. • Design methods of torsional capacities of H-CFST columns under cyclic pure torsion and compression-torsion are proposed. Concrete-filled steel tube (CFST) columns have been widely used in the construction industry because of their excellent compression capacity and torsion resistance. Regarding traditional CFST columns, the H-CFST column with an additional H-section steel member embedded in the core concrete provides improved fire and compression resistance. In this study, the seismic performance of nine H-CFST columns under cyclic torsional and compression–cyclic torsional loads was experimentally analysed. In the experiments, the failure mode, torque versus torsional angle hysteresis, torque versus torsional angle skeleton, torsional stiffness degradation, and energy dissipation capacity were determined. The hysteretic curves of the H-CFST columns under torsion were relatively plump in shape and exhibited no 'pinching' phenomenon, and the torsional stiffness of the H-CFST columns under unloading and reverse loading was approximately equal to the initial torsional stiffness. In addition, the applied compression had remarkable effects on the torsional capacity, torsional ductility, torsional stiffness, and hysteretic loop energy dissipation of the H-CFST columns. The shear capacities of the steel and concrete under normal stress or combined normal and shear stress were determined based on the latest theories and test results. Moreover, design method for the determination of the torsional capacity of H-CFST columns under compressive torsion is proposed based on the test results, and the theoretical contribution ratio of the H-section steel, steel tube, and concrete in the H-CFST columns to the torsional capacity was determined. [ABSTRACT FROM AUTHOR]