Study of mechanical performance of concrete-filled steel tubular joints

Abstract eng:
With the development of large span and heavy load modern engineering, concrete-filled steel tubular truss and laced column structures appear constantly. The joints of these structures are mostly circular Concrete-Filled Steel Tubular (CFST) joints. In order to solve the problem of lacking of the research on the mechanical properties of CFST joints, three CFST T-joints and one Circular Hollow Section (CHS) T-joint which was used for comparing were tested under reversed cyclic axial loading, and three CFST T-joints and one CHS T-joint were tested under reversed cyclic in-plane bending loading. The failure modes and the ultimate load carrying capacities of CFST T-joints were concluded and the load-displacement hysteretic curves were also studied. The test results showed that the failure modes of CFST joints and CHS joints with the same geometry were completely different, the ultimate load carrying capacities of CFST joints were much higher than that of CHS joints, which shows that adopting a concrete-filled chord member is the most effective way to improve the strength of the unstiffened tubular joints when subjected to axial loading and in-plane bending, the energy dissipation mechanisms of CFST joints and CHS joints were completely different, but both CFST joints and CHS joints had excellent seismic performances. The energy analysis of CFST joints under differing loading conditions indicated that there was a significant distinction in terms of the energy dissipation mechanism. The axially loaded specimens dissipated energy mainly by plastic deformation of the brace, while the in-plane bending loaded specimens dissipated energy mainly by punching shear of the chord wall at the intersection area. This research can not only provide scientific basis for the design of CFST joints, but also effectively promote the application of CFST truss and laced column, and can promote the improvement and development of the design theory of concrete-filled steel structures.

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