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Box concrete-encased, concrete-filled steel tube (CFST) piers have been used in bridges in high-earthquake-intensity regions in China in recent years. They are expected to have higher strength and better ductility than normal box reinforced concrete members owing to the contribution of CFSTs in the corners of the composite box section. However, studies on this type of composite piers are limited. This paper presents an experimental study on the behaviour of box concrete-encased CFST columns under eccentric compression. A total of 14 specimens, including 12 box concrete-encased CFST specimens and two reference box reinforced concrete specimens are tested. The main parameters in the test are height-to-width ratio and load eccentricity. A simplified method is proposed to predict the load capacity of the box concrete-encased CFST columns. [ABSTRACT FROM AUTHOR]

The welded truss composed of circular hollow section (CHS) braces and concrete-filled circular hollow-section (CFCHS) chords is a new kind of structural system that has been increasingly applied in large span arch bridges in China. It is necessary to have a good knowledge of fatigue strength of the welded CHS-to-CFCHS joints for the design of this kind of composite bridge. This paper reports on a series of tests on welded CHS-to-CFCHS T-joints subjected to axial cyclic fatigue loading in the brace. Eleven joints were designed to investigate various influence factors such as different nondimensional geometric parameters of circular hollow sections and different concrete strength grades. The quality of welds connecting brace and chord members were examined using the magnetic particle and radiographic inspection methods. The conditions of hot spot stress at both the crown and saddle positions in brace and chord members were determined by means of linear and nonlinear extrapolation methods. During the fatigue testing process, the number of cycles relating to several stages of failure, the crack initiation positions, crack propagation patterns, and the final failure modes were recorded. Fatigue strength of the CHS-to-CFCHS T-joints was compared with that of CHS-to-CHS T-joints. It is concluded that the CHS-to-CFCHS T-joints have a much lower stress concentration factor and consequently have better fatigue strength than the CHS-to-CHS T-joints, when both kinds of joints have the same nondimensional geometrical parameters and same nominal stresses on the brace. The curves in the Comité International pour le Développement et l'Étude de la Construction Tubulaire guidelines used for CHS-to-CHS joints are not appropriate for the reliable fatigue assessment of CHS-to-CFCHS T-joints based on the current test data. [ABSTRACT FROM AUTHOR]

Abstract: Recently, tapered concrete-filled double skin steel tubular (CFDST) columns have been applied in electricity transmission towers in China. However, there is still lack of information on the behaviour of such kind of members. This paper thus carried out the investigation on axially loaded tapered CFDST stub columns. The parameters included the tapered angle and the sectional profile. A finite element analysis (FEA) model was developed to predict the behaviour of the tapered member as well. The results showed that the steel tubes and the sandwiched concrete could work together well despite the tapered angle. The failure mode of the tapered CFDST stub column was similar to that of the straight one, and the failure occurred near the smallest section. The confinement effect of the tapered member was discussed by using the stress analysis. Finally, formulas were suggested for the calculation on the ultimate strength of the tapered CFDST stub column. [Copyright &y& Elsevier]