Cyclic Performance Of I-beam To Square Steel Tubular Column Connections Equipped With Superelastic Shape Memory Alloy Bolts

Traditional steel frame beam-column connections dissipate energy mainly through deformation of beam members to against seismic loadings,and there is often irrecoverable residual deformation after earthquake,which is very difficult to repair,and brings great challenges to post-earthquake repair work.The self-centering connections can solve the problem of residual deformation.Shape memory alloy(SMA)is a kind of intelligent material,which has the shape memory characteristic and superelastic.After large deformation,its deformation can be recovered by heating or unloading.When applied to beam column joints,the joints can obtain good self-centering ability and reliable cyclic performance.In this paper,The I-beam to square steel tubular column connections equipped with superelastic SMA bolts were designed according to the thought of "strong member weak connection",which can recover the deformation after unloading.The following work was carried out by using the research method of combination of experimental research and finite element analysis:(1)Three I-beam to square steel tubular column connections equipped with different screw lengths superelastic SMA bolts were designed.The hysteretic loading tests were carried out to analyze and compare the failure mode,strength,stiffness,ductility,selfcentering capacity and energy consumption ability of the connections.The test results showed that compared with the traditional high-strength bolt steel frame beam-column connections,the residual deformation of the connections was small and the self-centering performance of the connection was obvious;In the research scope of this paper,the influence of screw length on the bearing capacity of this connections was not particularly obvious.The connections with longer screw showed better joint ductility and self-centering ability,but the connections with shorter screw can obtain larger initial stiffness and energy consumption capacity.(2)The finite element analysis model of I-beam to square steel tubular column connections equipped with superelastic SMA bolts was established by ABAQUS package.The hysteretic curve,skeleton curve and cumulative energy consumption curve obtained from the experiment and finite element analysis were compared.It was found that the average errors of the experiment and finite element in the initial stiffness,yield strength,ultimate strength and total energy consumption were 10.67%,11.14%,-3.56% and 15.09%,respectively.In general,the results of finite element analysis are in good agreement with the experimental results,which shows that this finite element modeling method is reliable and effective.(3)Based on the verification of the finite element modeling method,this paper analyzed the parameters of the connection,and researched the influence of the thickness of the beam endplate,the pretightening force of SMA bolts,the arrangement of SMA bolts and the group hybrid of SMA bolts and high-strength bolts on the connection performance.According to the results of experimental and parametric research,some design suggestions were put forward for this kind of connection,including the details of the bolt structure,the bolt arrangement,the bolt preloading and the thickness of the beam endplate.