| With the continuous development of building structure,the advantages of high bearing capacity and small section size of the concrete-filled steel tube(CFST)structure have become more prominent.Among them,the CFST column-beam joint is an important part of the CFST structure.Based on actual engineering needs,this paper proposes a new type of corbel nonpenetrating CFST column-reinforced concrete beam(RC)joint,and designs related experiments to study the mechanical properties of the new joint.The finite element analysis software ABAQUS is used to simulate the whole process of test loading,and after the accuracy of the finite element model is verified,the influence of different parameters on the mechanical properties of the joints is further discussed.The research results of this paper have a certain academic value for the study of the mechanical properties of CFST joints,and also provide a theoretical basis and design reference for engineering practice.This main research works are as follows:(1)Two new joint specimens were designed,and the beam end monotonic load test and the beam end low-cycle reciprocating load test were carried out.From the failure mode,crack distribution,load-displacement curve,strain situations of steel bars and steel,this paper analyzes and discuss the test results.The test results show that the new joint reliably transfers the load from the beam end to the steel tube through the steel corbel,and the reinforced concrete beam section at the cantilever end of the corbel undergoes bending failure,and the bearing capacity meets the requirements,indicating that reasonable design can achieve "strong joint and weak member" seismic design principle.The strength and stiffness of the new joints are not significantly degraded under repeated low-cycle actions,and the mechanical properties are stable.The new joint longitudinal reinforcement anchoring form can effectively resist the slip of the steel bar,and ensure that the steel,concrete and steel corbels can work collaboratively.(2)The finite element analysis software ABAQUS is used to simulate the whole process of test loading.The finite element results are basically consistent with the test results,which further reveals the force mechanism of the new joints.On this basis,a parametric analysis is carried out,and 11 design parameters such as the length of the section steel corbel,the thickness of the flange plate and the thickness of the horizontal ring plate are selected for research.The results show that increasing the length of the section steel corbel can effectively improve the stiffness and bearing capacity of the joint.Increasing the thickness of the corbel flange can improve the stiffness and bearing capacity of the joint to a certain extent,but the lifting amplitude decreases rapidly with the increase of thickness.Increasing the width of the horizontal ring plate can increase the stiffness and bearing capacity of the joint,and reduce the stress level at the junction of steel tube,horizontal ring plate and flange plate.The new joint is less affected by some parameters such as the axial compression ratio,the strength of the steel tube concrete,the steel tube thickness and so on,therefore the designers should pay attention to the balance of economy and safety.(3)Combining test and finite element results,this paper describes the working mechanism of the new joint,proposes the calculation methods of the bending moment of beam end and steel corbel end,and proposes a segmented design method.Then this paper proposes some feasible designed and constructed suggestions about the length of the steel corbel,the width of the horizontal ring plate,the anchoring of steel bars,the reinforcement of stirrups and so on. |
