Static Performance Study Of Concrete Filled Steel Tubular Members With Defects Under Combined Compression-Bending-Torsion Loading

The concrete-filled steel tube composite structure combines the advantages of steel pipes and concrete to give it outstanding mechanical properties,so the concrete-filled steel tubular members have been widely used.However,in actual engineering,the combination of steel pipe and concrete is flawed.One is the phenomenon of bubbles and bleeding caused by pumping the core concrete,which leads to the formation of spherical crown-shaped void;Because the component is subjected to vertical load,the shrinkage and creep of the concrete will be formed during the application process,which will cause the formation of annular void defects,which will affect the mechanical properties of the component.Based on the experimental research,this paper theoretically analyzes the mechanical properties of concrete-filled steel tubular members with voids under compression and torsion.The specific work is as follows:(1)The research progress of the research on the hollowing of concrete-filled steel tubular members and the research status of the composite under-load of concrete-filled steel tubular members are reviewed.(2)The static test of 22 concrete-filled steel tubular members with voiding defects under compression,bending and torsion is carried out,including 2 empty steel pipe test pieces,8 non-empty test pieces and 6 spherical crowns.Shaped void test piece,6 ring-shaped hollow test pieces,the test parameters are axial compression ratio,bending-torque ratio and void type.(3)Based on the rational constitutive model of selected materials,the numerical simulation of concrete-filled steel tubular members with voiding defects under the action of bending and torsion is established,and the accuracy of the model is verified by the test results.(4)The finite element software was used to establish the model of pure torsion members and compression-bending-torision members of concrete filled with hollow steel.The load-displacement curves of various parameters were analyzed and the influence on the bearing capacity coefficient was analyzed.The effect on the mechanical properties of the component.On this basis,the engineering suggestions for the members with annular voiding defects and the reduction formula for the members with spherical crown-shaped voids are given.