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Based on two quasi-static experiments of steel tube confined reinforced concrete columns (STRC) under pure torsion load, detailed finite element (FE) simulation and theoretical derivation of the corresponding calculation methods were conducted in this paper. FE models of STRC specimens under pure torsion were established using the finite element software ABAQUS, the feasibility of which was then validated against the testing results in terms of both ultimate torsional capacity and failure modes. Comprehensive parametric analysis was presented, including the yield strength of steel tube, the thickness of steel tube, the dimension of cross-section, the strength of concrete, the yield strength of longitudinal reinforcement, the ratio of longitudinal reinforcement, the yield strength and the ratio of stirrup, to investigate the influence on the torsional capacity of STRC columns with important structural factors. It can be found from the parametric analysis results that, the thickness of steel tube, the dimension of cross-section and the ratio of longitudinal reinforcement are the most important parameters for the torsional capacity of STRC. Based on the results parametric analysis, an accurate and simplified calculation method for the ultimate torsional capacity of STRC columns under pure torsion was proposed.

In order to study the mechanical behavior of steel tube confined reinforced concrete (STRC) columns under combined compression-bending-torsion, an experimental investigation was conducted. The load–deformation hysteretic curves and the strain distribution law of steel tubes under pure torsion, bending-torsion and compression-bending-torsion loads were obtained. Results show that a ‘pinch’ effect appeared in the load–deformation hysteretic curves of STRC under pure torsion and bending-torsion loads, however, this was not noticeable for specimens under compression-bending-torsion load. When the axial compression ratio was relatively small, STRC columns under compression-bending-torsion load showed higher bending capacity and torsion capacity than that under bending-torsion load, as well as good energy dissipation capacity. Furthermore, the strain of the steel tube increased linearly with the load, and the corresponding stress was always below the yield strength. Based on the test results, the enhancement of the bending and torsion capacities of reinforced concrete columns caused by steel tubes, and the reduction of the bending capacity of STRC columns caused by torque were analyzed.

Tapered Concrete-Filled Double Skin Steel Tubular (CFDST) columns have been commonly used in structures. To report further information, it is necessary to perform more studies on the structural behaviour of tapered CFDST columns, especially for those with high hollow ratios. This paper thus conducted an investigation on the tapered CFDST stub columns under axial compression. Specimens with varied tapered angle, hollow ratio and tubes' thickness were tested, and then typical failure modes, load versus displacement relations as well as strain development were revealed. Validated finite element models were given to further analyse the columns' structural mechanisms including the stress distributions, the interaction between the steel tubes and the sandwiched concrete, and the influence of main parameters. The ultimate strength of specimens was calculated tentatively using the methods in the existing design guidelines, and their accuracy and applicability for the tapered CFDST stub columns with high hollow ratios were preliminarily evaluated. A simplified method was suggested to predict the ultimate strength based on one of the guidelines, and the predictions show reasonable agreement with the test results.

In this paper, a simplified seismic design method of high-rise frame-steel plate shear wall (SPSW) system was proposed based on the multi-modal-analysis under the framework of performance-based seismic design. The seismic response of high-rise SPSW system was simplified to first and multiple-modal equivalent single degree-of-freedom (SDOF) oscillators. The dual frame-SPSW structure was decomposed into a frame system and SPSW system by controlling the relative contribution of SPSW system, and they were correspondingly simplified to a series of F-SDOF oscillators and S-SDOF oscillators. The analytical models of F-SDOF and S-SDOF oscillators were developed using the modal pushover analysis. By assuming the system responding linearly elastic for higher modes, the equivalent SDOF oscillator (D-SDOF) for the frame-SPSW system was developed by combining the F-SDOF and S-SDOF oscillators in parallel for each mode of vibration. The design procedure was developed based on the comparison of displacement thresholds against the displacement demands derived using the SRSS combination. A 15-story frame-SPSW system was adopted to verify the feasibility and demonstrate the design process of the simplified method. The result also shows the seismic demands derived by the equivalent dual SDOF oscillators have good consistency with that by frame-SPSW structure.

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.

The concrete-filled steel tube (CFST) column circumferentially confined by carbon fibre reinforced polymer (CFRP), i.e. CFRP-CFST column, is a promising structural member in engineering practice. In this paper, the torsional capacity of CFRP-CFST columns was investigated by means of finite element (FE) simulation and theoretical derivation. Comprehensive FE models were established considering suitable material constitutive laws and interface relationships, which were then verified by experiment results. Besides, parametric analysis was conducted to reveal the geometrical and material parameters' effects on the torsional capacity of CFRP-CFST columns. The results show that the yield strength, the thickness, and the outer diameter of the steel tube are the most influential factors, and the number of CFRP layers also affects the torsional capacity considerably. Meanwhile, the comparison between the CFRP-CFST and CFST column indicates that the confinement effect provided by the CFRP can enhance the torsional capacity. Finally, equations for calculating the torsional capacity of the CFRP-CFST column were proposed and proved to be accurate through comparison with the test data.

Steel plate shear wall (SPSW) buckling-restrained by hat-section cold-formed steel is a new type of lateral bearing system that uses hat-section cold-formed steel members to restrain the buckling deformation of the SPSW. Integration of architectural and structural functions is achieved in this new shear wall system by externally bonding oriented strand board (OSB) and filling sound insulation material. A finite element (FE) model was developed and validated against seven experimental results in terms of failure modes, shear force-story drift angle curves and shear bearing capacities. Upon validation, an extensive parametric study was carried out to investigate the six key parameters including spacing of connecting bolts, geometries of hat-section steel, spacing of hat-section steel, steel material strength, width-height ratio of the SPSW and height-thickness ratio of the SPSW. Based on the 104 numerical results, new design rules are proposed to predict the stiffness, shear yielding strength and shear ultimate strength of this new type of buckling-restrained SPSW structure. By comparing the predicted results with experimental and numerical results, the proposed design method is found to be accurate and consistent. In addition, an equivalent cross-bar model is developed as a simplified substituted SPSW model to be used in theoretical modelling programmes in the future.

The concrete-filled steel plate (CFSP) composite coupling beam is a newly developed form of coupling beam that possesses high deformation and energy dissipation capacities. In this paper, the shear capacity of concrete-filled steel plate composite coupling beams was investigated. An analytical model was proposed based on the force mechanism of the composite coupling beam and was proved to have adequate accuracy compared with the available test results. The shear capacity of the composite coupling beam was found to be governed by flexural strength, shear strength, or flexural-shear strength, depending on the material and geometrical properties of the coupling beam. By incorporating the effect of flexural-shear interaction, a unified equation was finally developed.

Concrete-filled steel tube-enhanced steel plate-reinforced concrete (CFST-SPRC) shear walls have been proposed for use in super high-rise buildings. This paper presents an experimental study of CFST-SPRC shear walls that aims to evaluate their seismic behavior. Three CFST-SPRC shear wall specimens with varying steel plate thicknesses and concrete strengths were tested under constant axial force and reversed cyclic loading. All of the specimens experienced a progression of failure from web concrete cracking, to local buckling of the steel tube plates, to fracturing of the vertical welds at the corners. One specimen exhibited brittle failure at the end of testing due to the sudden crushing of web concrete. Stable and full hysteretic behavior was developed by the shear wall specimens, indicating a capability for stable energy dissipation. The ultimate drift ratios were around 1.7% for all of the specimens. The flexural and shear deformations of the shear walls, and the base rotation caused by local deformations in the foundation beam, all provided a negligible contribution to the total lateral displacement. The proportions of the flexural displacement, shear displacement and rotational displacement to the total displacement were around 0.6, 0.2 and 0.2, respectively, for all specimens throughout the loading process. Simplified design methods were proposed for evaluating the load-carrying capacities of CFST-SPRC shear walls. The proposed method provided reasonable but conservative estimations for the test shear wall specimens.

Concrete filled steel tubular (CFST) members are efficient structural members and have been widely used in seismic areas. The effective stiffness of CFST members is important in the structural design for determining the buckling capacity of a member, and evaluating the elastic deformations and internal forces of a structure, but current understanding is not sufficient on it. To address this, a theoretical modal was developed on the basis of a perfect bonding assumption and assumed strain distributions. Design equations were derived and errors induced by the assumptions were corrected using finite element analyses. The proposed equations for the effective flexural and shear stiffness of section consist of the full stiffness of steel tube and a reduced stiffness provided by the concrete infill. The reduction factors for the concrete contribution are related to the level of axial force and the ratio of axial stiffness of steel to concrete. From investigation of available test results, it was found that the proposed equations could well predict the stiffness of CFST members under different loading conditions, and could be used in engineering practice.

A self-centering beam (SCB) is an innovative shop-fabricated structural member incorporating a gap-opening mechanism into its body. This beam can exhibit self-centering characteristics by using high-strength post-tensioning strands and by dissipating seismic energy by combining pretensioned bolt frictional devices. This paper describes a step-by-step seismic design of self-centering-beam moment frames (SCB-MFs). A series of 3-, 6-, 9- and 12-storey steel frames is designed using this procedure. Fabrication tolerances are included in the model to investigate the effects of beam length tolerance on the seismic responses of SCB-MFs. Nonlinear time history analyses are conducted on these frames under an ensemble of 20 historical earthquakes. The same buildings are designed as ‘special moment frames’ according to ASCE 7–16 for seismic comparison. The results suggest that the proposed SCB-MFs with fabrication tolerances can achieve comparable maximum seismic performance and eliminate residual drifts compared with traditional moment frames of an equivalent beam size and having fully restrained connections.

In recent years, the application of steel-concrete composite beam has gained popularity due to its mechanical property, economical and construction efficiency. However, in the negative moment areas, tension occurs in the concrete deck, which is undesirable and needs to be carefully addressed. As a result, prestressing tendons were used in the precast concrete deck by pretensioning, which can effectively solve the cracking problem of concrete deck in negative moment of a continuous composite beam and avoid steel beams consuming partial prestress. This paper presents 8 experiments which were designed to verify the mechanical property of assembled monolithic steel-prestressed concrete composite beams (AMS-PCCB) in negative moment. Shear stud groups (SSGs) or steel block shear connectors (SBSCs) were used in the AMS-PCCB. The effects of shear connector, prestressing, deck width, and deck processing technique on the flexural capacity, interface slip, and crack development of the composite beam in negative moment were investigated. The test results show that the prestressing tendons improve the cracking load significantly, while it has no obvious influence on the flexural capacity. So, the flexural capacity of the composite beam in negative moment can be calculated using the plastic analysis method without the consideration of prestressing tendon. Based on the test results and available calculation methods, modified methods for determining the crack spacing and width in a negative moment region were proposed.

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.