Research On The Mechanical Behavior Of CFST Columns Circumferentially Confined By CFRP Under Combined Compression-Bending-Torsion Load

Carbon fiber reinforced polymer(CFRP)confined concrete filled steel tube(CFST)column(CFRP-CFST)is one of the composite structures,in which CFRP is circumferentially wrapped around the CFST column.It takes advantages of the CFST column,such as high load bearing capacity,good ductility,excellent seismic performance and easy construction.Moreover,the wrapped CFRP can delay or even restrict the buckling of steel tube,enhance the confinement provided to the core concrete,and solve the corrosion problem of the steel tube.CFRP-CFST columns may subject to complex loads in practice,therefore,the mechanical properties of CFRP-CFST columns under conbined compression-bending-torsion load were investigated in this paper.The main research works are shown as follows:?Pseudo-static tests of 5 CFRP-CFST columns and 3 CFST columns under pure tosion,bending-torsion and compression-bending-torsion loads were carried out.The failure modes,load-deformation curves,and strains of steel tube and CFRP were obetained.The load bearing capacity,ductility and energy dissipation capacity of CFRP-CFST columns and CFST columns were compared.The influence of CFRP layer number and different loading mode on the load bearing capacity,ductility and energy dissipation capacity of CFRP-CFST columns were investigated.Based on the test results,the applicability of the existing calculation formulas for the load bearing capacity of CFRP-CFST columns was evaluated.?Finite element models of CFRP-CFST columns and CFST columns under pure tosion,bending-torsion and compression-bending-torsion loads were established using ABAQUS.The accuracy and reliability of the model were verified aginst the load bearing capacity and failure mode of the test results.?Parameter analysis was carried out based on the finite element models.The influence of the strength,layer number and constraint height of CFRP,yield strength,thickness and diameter of steel tube,concrete strength,and the axial load ratio on the load bearing capacity and initial stiffness of CFRP-CFST columns under pure tosion,bending-torsion and compression-bending-torsion loads were investigated.The method for the determination of CFRP constraint height under different loading modes was proposed.Based on theoretical analysis and parameter fitting method,the calculation methods for the torsional bearing capacity of CFRP-CFST columns under pure torsion was proposed,and correlativity expressions under bending-torsion and compression-bending-torsion loads were presented.The proposed expressions were with simpler form and higher precision.