Study On Mechanical Behavior Of Steel Tube Confined Rc Columns Under Combined Compression-bending-torsion Load

In order to study the mechanical behavior of steel tube confined RC(STRC)columns under combined compression-bending-torsion,experimental research,finite element model simulation,derivation of calculation methods of bearing capacity and suggestion of constructional optimization were conducted in this paper focus on STRC columns under pure torsion,bending-torsion and compression-bending-torsion loads.(1)Six STRC specimens were tested.The failure modes,load-deformation hysteretic curves and the strain distribution laws of steel tubes under pure torsion,bending-torsion and compression-bending-torsion loads were obtained.The force mechanism,ductility,energy-dissipating capacity and change rules of bearing capacity were carried out sequentially.(2)Finite element models of STRC specimens under pure torsion,bending-torsion and compression-bending-torsion loads were built through ABAQUS,and the modeling process was specified.The similarity of bearing capacity and failure modes between the results of tests and finite element models verified the accuracy of finite element models.(3)Based on the abundant results of finite element model simulation,the influence rules of strength and thickness of steel tubes,strength of the concrete,strength and diameter of longitudinal reinforcement and stirrup on bearing capacity of STRC columns were carried out.Besides,the accurate and succinct calculation methods of bearing capacity and correlation expression between bending and torsion capacity of STRC columns under pure torsion,bending-torsion and compression-bending-torsion loads were obtained.(4)Two methods were proposed to optimize the failure modes of STRC columns under compression-bending-torsion load,including increasing longitudinal reinforcement and increasing stirrup locally near the tube's girth gap.The optimization effect of these two methods were studied by finite element models,according to the simulation results,constructional optimization suggestions are given in the end.