Load-bearing capacity of CFDST based on the unified strength theory

摘要

Based on the unified strength theory presented by Maohong Yu, the calculating formula for the load-bearing capacity of concrete-filled double steel tube was derived. Through tests, the calculating load-bearing capacity results were compared with testing results, which agreed well. The change of load-bearing capacities with parameter k of the unified strength theory was discussed. It can be drawn that the load-bearing capacity of CFDST will increase with the increase of parameter b, but the increase is not obvious. Concrete-filled steel tube (CFST) is a kind of composite members that normal concrete is filled into thin-walled steel tube. Compared with normal concrete, it possesses many merits. The most notable merits are the yoke effect, which can improve the yield strength of core concrete, can increase the plasticity, ductility and the load-bearing capacity, also can be convenient for construction, and very economic. So this kind of members is used in civil engineering in China widely, such as bridge engineering, building engineering. Scholars all over the world have done many works on CFST, and developed several forms, such as concrete filled steel tube (CFST), concrete-filled double steel tube (CFDST), concrete filled rectangular steel tube (CFRST), concrete filled double rectangular steel tubes (CFDRST) and section steel reinforced concrete filled steel tube (SSRCFST), which are shown in Fig.1. As for CFST, there are many studies. Han (2000) summarized the static and dynamic properties of concrete-filled steel tubular members, and presented the calculating formula for member designs, such as axial compression stiffness, axial compression strength and stability. Zhang (2002) presented the axial compression strength of CFST based on the plasticity theory, and conducted specimen tests to verify the method. Xia (2010) derived the load bearing capacity of CFST based on the unified strength theory presented by Yu (2004), discussed the calculating parameters of k and b in the unified strength theory, and compared the calculating results with testing results of specimens, which reflected the correction of the derived calculating formula and the unified strength theory. Now based on the same theory of the unified strength theory, we derived the calculating formula of load-bearing capacity for CFDST, to direct the designing of CFDST in bridge and building engineering.