Performance Analysis Of Buckling Restrained Braced Steel Frame Under Mainshock-aftershock Sequence

The buckling restrained brace(BRB),which restrains the inner core from being bent by the restrained unit,overcomes the disadvantage that the conventional brace is prone to buckling instability under pressure and has been widely used in engineering.However,the post-yielding stiffness of BRB is low,and it is hard to ensure the BRB in the structure can enter the yielding statge at the same time when the earthquake occurs.In the buckling restrained braced steel frame with BRB as the main energy-dissipating and lateral-resisting components,it is prone to occur damage concentrated and large residual deformation.After high-intensity earthquakes,there are usually many aftershocks with high levels of seismic damage.This may cause BRB subjected to large earthquakes will continue to undergo low-cycle fatigue failure due to multiple cyclic loads,causing structural collapse.Based on different parameter indexes,probabilistic seismic performance of BRBF under the mainshock-aftershock sequence was investigated.The research contents are as follow:Firstly,a numerical analysis model for the simulation of BRB fatigue failure was established.The Fatigue material based on Coffin Manson model and Miner criterion was used to simulate the fatigue failure of BRB under cyclic loading.The feasibility was verified based on the existing experimental data.This will provide the basis for the collapse fragility analysis of the BRBF under the mainshock-aftershock sequence.Secondly,the mainshock-aftershock sequence was constructed by repeated synthesis and random combination,and the as recorded mainshock-aftershock sequence was selected as a comparison.Based on the different parameters of ground motion intensity,the statistical analysis and evaluation descriptions of the ground motion intensity of different combinations of mainshock-aftershock sequence were carried out.Then,seismic fragility probability of the BRBF structure under the mainshock-aftershock sequence was analyzed.The differences in the collapse fragility of BRBF under the mainshock and the mainshock-aftershock sequence are compared by the peak drift,the residual drift and the modified Park-Ang damage index.Finally,seismic demand risk probability of the BRB components under the mainshock-aftershock sequence was investigated.Taking BRB's maximum plastic deformation rate and cumulative plastic deformation rate as indicators,the proposed BRB performance demand recommendation values for considering the influence of aftershocks under Design Basis earthquake level and Maximum Considered Earthquake level are given,which provide reference for practical projects.