Research On The Lapped Self-centering Buckling-restrained Brace With SMA Rod And Its Seismic Performance In The Structure

Self-centering buckling-restrained brace is a type of seismic resisting member for structures,which could not only improve the energy dissipation capacity but also decrease the residual deformation of a structure.The SCB with steel tubes and pretensioned rods is widely researched for its significant advantages such as large resisting capacity and so on.However,though a relatively large elastic elongation could be obtained on the SCB with pretensioned rods,the pretensioned rods may fail in fracture by a large strain under a large lateral displacement.Furthermore,the length and weight of the double-tube on the SCB is also a deficiency with large length demand on the pretensioned rod.This paper proposed a type of lapped self-centering buckling-restrained brace(SC-BRB)combining the shape-memory alloy(SMA)and lapped steel tubes,named lapped self-centering buckling-restrained brace with SMA rod(lapped SMA-SCBRB).The SMA rod could behave a large recoverable strain which could improve the self-centering capacity of SCBRB,and an experimental study on the material performance of large diameter SMA rod is conducted.The theoretical and numerical study is conducted for obtaining the mechanism of the lapped SMA-SCBRB and its seismic performance on the structures.The main contents are listed below:(1)The construction and working principle of the lapped SMA-SCBRB is deeply analyzed.The loading process of the lapped SMA-SCBRB is studied,and the stiffness equations for each stage for the first loading procedure are deduced.The hysteretic model and the critical parameters for the SMA-SCBRB is also determined.The basic design process for the lapped SMA-SCBRB is conducted and a design example is provided.(2)The material property test on the SMA rod produced by different manufacturers in China are conducted,and the mechanical property on the SMA rod influenced by the cycle numbers,strain amplitude and loading rate are discussed based on the Martensite phase transformation stress,hysteretic property,equivalent viscous damping ratio and residual strain.The testing result indicates that the material performance of SMA producted in China is not so stable,and the cycle numbers,strain amplitude,loading rate and heat treatment method may significantly effect the material property of SMA.(3)The finite element analytical model for lapped SMA-SCBRB is conducted based on ABAQUS.The constitutive relation for SMA is effectively modeled by the piecewise linear constitutive model.The effect on the hysteretic performance of the self-centering system caused by the initial pretension Fp is discussed The results indicate that improving Fp could significantly improve the self-centering capacity under the condition ?P<?P4,in which ?P stands for the initial pretension stress;However,this improving effectiveness may be decreased under the condition ?P>?P4.The numerical analysis results indicate that the lapped SMA-SCBRB can behave a significant self-centering capacity and stable hysteretic property.(4)The rheological model for simulating the hysteretic property of the lapped SMA-SCBRB is conducted.This model has explicit in physical conception which could effectively simulate the monolithic hysteretic property.The simulating result is compared with the finite element analytical result obtained by ABAQUS.The rheological model is used to study the effect on the hysteretic property of SMA-SCBRB by the indexes such as initial pretension FP,the first strength ratio ?1,the second strength ratio ?2,the lap length coefficient y and temperature T,which is a basic for the structural analysis.(5)The motion equation for single-degree-of-freedom system to lapped SMA-SCBRB is derived,and 20 seismic waves are selected for lapped SMA-SCBRB hinged frame to conduct the nonlinear time history analysis under the design based earthquake and rare earquake,respectively.The influence law on four indexes(including seismic reduction factor R,the first strength ratio ?1,the second strength ratio ?2,the lap length coefficient ?)to seismic performance of a 4-storey lapped SMA-SCBRB hinged frame.The result indicate that the decrease of the reduction coefficient R could significantly reduce the maximum inter-story drift of the structure,however,it has little influence on the self-centering capacity.This paper suggest the R to be 8.Furthermore,the decrease of ?1 will raise the maximum inter-story drift and residual drift,and the decrease of ?2 and ? could also reduce the maximum inter-story drift,however,it have littile effect on the residual drift on the structure.