Experimental Study And Theoretical Analysis Of Semi-rigid Joints To Circular CFDST Columns

Compared with the circular concrete-filled steel tubular(CFST)column joints,tests and studies of circular concrete filled double skin steel tubular(CFDST)column joints are little.Following the California earthquake in 1994 and Japan Kobe earthquake in 1995,scholars found that rigid connections had poor ductility capacity and field welding technique.Some scholars put forward the blind bolted end plate joints.The advantages of the typed joints were convenient construction and good mechanical performance.In this paper,seismic experiments and theoretical research on the behavior of semi-rigid joints to circular CFDST columns were investigated.The results were summarized as follows:(1)The nonlinear finite element(FE)analysis of semi-rigid joints to circular CFST columns under static load were conducted by software ABAQUS.The accuracy of the FE models was examined by the experimental results in the field of moment-rotation relationships and failure modes.The effects of the twelve factors on the performance of the novel joints were studied.This chapter had solved the problem of contact modeling among circular surfaces in FE models,providing a base to studying the circular CFDST counterparts in chapter four.(2)Four cyclic loading tests were conducted on the flush or extended end plate joints to circular CFDST columns with blind bolts to explore the effects of the end plate type and the column hollow ratio.The failure mode,the moment-rotation hysteretic curves,energy dissipation etc.were also analyzed.(3)Based on the results of circular CFST column joints,a nonlinear FE modeling study on the circular CFDST column joints under monotonic loading was conducted.The nonlinear full-range analysis of the typical joints was executed.The failure modes were also studied including deformation of the end plate,anchorage fracture of the tensile bolts,outward deformation of the column flange and etc.(4)The effects of thirteen factors on the mechanical performance on the circular CFDST column joints were analyzed by using FE software ABAQUS.(5)According to the experimental and FE results,some reasonable structural measures were discussed such as welding internal rings,welding external C-channels,setting level axillary on beam flange,stiffening ribs on extended endplate etc.which could improve the moment capacity and initial stiffness of the composite joints.With the development of the building industrialization,the typed joints mentioned are advised to be use d in the engineering application in the future.