Experimental Study On Mechanical Behavior Of Circular Concrete Filled CFRP-Steel Tubes Under Compression-Bending-Torsion

With the development of society,the structure and form of buildings have changed,and the concrete-filled steel tubular(CFST)are widely used because of its excellent mechanical properties.However,buildings will be damaged by natural disasters,and the complexity of the building form also requires higher performance of structure.For the purpose of repairing the damaged CFST and improving the performance of CFST structure,CFRP with light weight,high strength,fatigue resistance and corrosion resistance is used in civil engineering.Concrete filled CFRP-steel tubes is a kind of structure formed by pouring concrete into CFRP-steel tubes,or using CFRP to reinforce damaged CFST.This paper will research the mechanical behavior of circular concrete filled CFRP-steel tubes under compression-bending-torsion.The contents include:(1)based on the test,9 specimens were designed with axial compression ratio(n),bending moment ratio(m)and longitudinal CFRP layers(m_l)as variables.The test results show that:the ductility of the specimen is good;CFRP can work with the steel tube until the CFRP fracture;increasing the axial compression ratio in a small range(n<0.4)will improve the bearing capacity of the specimen,but when n?0.4 will weaken the bearing capacity and ductility of the specimen;longitudinal CFRP can slightly enhance the torsional bearing capacity of the specimen;the three parameters have no significant impact on the rigidity of the specimen.(2)The finite element software ABAQUS is used to simulate the circular Concrete filled CFRP-steel tubes members under compression-bending-torsion,and the calculation results are in good agreement with the test results.(3)The parameters of core concrete strength,steel pipe strength,steel ratio,axial compression ratio,bending moment ratio,transverse CFRP layers and longitudinal CFRP layers are analyzed by using the finite element model.The results show that only the increase of steel ratio can significantly enhance the initial stiffness of T-?curve;the parameters that can affect the torsional capacity of the specimen include concrete strength,steel strength,steel ratio,axial compression ratio and the number of transverse CFRP layers,of which the steel ratio has the most significant effect;the increase of axial compression ratio in a small range(n<0.4)can improve the torsional capacity of the specimen,but beyond a certain range(n?0.4),the ductility and torsion resistance of the specimen will decrease;with the increase of the number of longitudinal CFRP layers,the effect of strengthening the torsion resistance of the specimen is limited;when the axial compression ratio is fixed,the increase of the bending moment ratio will reduce the torsion resistance of the specimen.