Nonlinear Finite Element Analysis On The Hysteretic Behavior Of New Type Exterior Joint In CFST With Various Axial Force Ratios

The dissertation is the further research of the concrete filled steel tube (CFST) joint with the core steel tube which was presented by Prof Wang Yihong. On the basis of nowaday shear bearing theories of the CFST, the shear bearing behavior of the new type CFST joint was analysed concretely, and one corresponding shear bearing capacity formula was presented. The joint region is composed of two portions: one portion is the concrete filled core steel tube, other portion is ring-renforced concrete outside the core steel tube. The shear bearing formula which is based on the Limit Analysis Theory presented by Cai Shaohuai, is composed by two portion shear bearing formula's simply adding with the influence of axial force ratios and ratio of shear span to effective depth of section.The analyse on the hysteretic behavior of this point with various axial force ratios are made by the finite element analysis (FEA) software ANSYS, with the basis of experimental models. In this dissertation, the new type CFST exterior joint as an example was analysed by finite element method. The definition of element type, real constent and and material property as well as subsequent modeling, meshing and solution controls were intruduced in detail in analytical process. By the FEA, the stress mechanism and failure process of every portion of the joint were showed, along with hysteretic behavior of the joint under various axial force ratios. On account of periphery concrete early cracking at column-RC beam joint region, the creep point of the joint was defined ahead of schedule. But the core steel tube and the ring-hoopings in joint region improved the joint strength, so the joint has good ductility. On the hysteretic analysis, the results showed that hysteretic curce of the joint was spindly. The joint had good engery-dissipation capacity. Based on the hysteretic curve, three paramaters about aseismatic behavior was analysed, including displacement ductile coefficient,loop-stiffness and energy dissipation coefficient. Compared with three parameters, it is found that the three parameters increases with the increasing of the axial force ratios, and reduces with increasing of the axial force ratios when the axial force is big enough. It indicates that the increasing of the axial force ratios is good for seismic in a certain bound.