Seismic Fragility Analysis Of Buckling-restrained Braces CFST Frame Structure Under Earthquake Sequences

A large number of historical seismic data show that more than 85%of earthquakes occur in the form of earthquake sequences.When structures are subjected to earthquake sequences,a large number of foreshocks or aftershocks will significantly increase the damage degree of structures,thereby increasing economic losses caused by earthquakes and aggravating casualties.Since cumulative damage of structures will be caused by the action of earthquake sequences,so it is necessary to study the adverse effects of earthquake sequence on structural performance.However,the current seismic design codes in China only consider main shock,ignoring the impact of earthquake sequence on structural performance.It is of great scientific significance and practical value to consider the adverse effects of earthquake sequence on structural performance.In this paper,80 real seismic motions are selected from PEER strong earthquake database as main shocks.According to the existing synthesis method of earthquake sequences,80 groups of earthquake sequences which can be reasonably applied to numerical simulation are synthesized.Buckling-restrained braces CFST frame structure is taken as the research object,which widely used at present.Based on ABAQUS finite element software platform,finite element model is established.The material subroutine of square tube concrete beam element is compiled,and the non-linear seismic response analysis of the structure under the action of single main earthquake and seismic sequence is carried out.The dynamic response of the structure under the action of main shock and seismic sequence is recorded,and the response pattern and cumulative damage development process of buckling-restrained braces CFST frame structure under the action of seismic sequences are explored.Based on the method of structural seismic fragility analysis,the peak acceleration of earthquake is selected as the index of seismic intensity,and the ISD%max is taken as the index of seismic response.The probabilistic seismic demand model is established,the limit state of structure is defined.The failure probability of structure exceeding the limit state under different seismic intensity seismic fragility curve are obtained.The seismic performance of the structure under earthquake sequences analyzed and evaluated.The results show that the seismic response of the structure increases obviously under the action of earthquake sequences.The damage probability under different performance levels increases significantly.The occurrence of earthquake sequences causes additional damage to the structure,which will aggravate the structural response and deterioration of structure performance.Therefore,in the seismic analysis and design of engineering structures,the adverse effects of seismic sequences on structure performance should be considered reasonably.