Seismic Fragility Study Of Self-Centering Braced Steel Frame Structure Considering Mainshock-Aftershock Seismic Sequences

Statistical data show that strong aftershocks or strong aftershocks often accompany the occurrence of strong main shocks.Because the interval between the main shock and the aftershock is too short to repair the structure,the occurrence of aftershock will aggravate the damage degree of the structure,even cause the structure to collapse,and bring great threat to people’s life and property.However,most of the current engineering seismic studies only consider the effect of a single earthquake,not yet the aftershock,it is of great theoretical significance and practical value to study the seismic behavior of engineering structures considering the action of main aftershock sequence.The self-aligning Braced Steel Frame（SC-BSF）structure has become a hot research topic in recent years because of its advantages of small residual deformation and low structural damage.In this paper,SC-BSF structure is selected to study the dynamic response and seismic vulnerability of the structure under the action of main and aftershock sequences of different strength.The main work is as follows:（1）A 9-story SC-BSF is taken as the prototype structure,and the equivalent prototype structure is designed by ETABS software.The correctness of the structure design is verified by strength check and deformation check;The key design parameters of each layer support are given,the numerical model of prototype structure is established by using OpenSEES platform,and the modal and period are compared with ETABS model,the validity of the numerical model is verified.（2）20 pairs of real main aftershock sequences are constructed and the SC-BSF structure is analyzed in dynamic time history.The results show that under the working conditions of small,moderate and large earthquakes,each response index increases with the increase of earthquake intensity,but the traditional response index,including structural base shear force,supporting axial force,floor relative acceleration,floor displacement,instantaneous vertical inhomogeneity coefficient,etc.,which are not sensitive to aftershocks,and response index based on residual displacement,for example,residual interstory displacement,residual vertex displacement and vertical non-uniformity coefficient can better reflect the cumulative process of aftershock damage.（3）The incremental dynamic analysis（IDA）of SC-BSF structure and the seismic vulnerability analysis of main aftershock sequences based on IDA are carried out by modulating the peak ground acceleration（PGA）of 20 pairs of main aftershock sequences to 9 strength levels respectively.The results show that aftershocks can significantly increase the degree of further damage of structures damaged by the main shock,and increase the probability of exceeding the limit state such as repairable and Life Safety The residual interstory displacement angle can reflect the deformation accumulation after earthquake,so it is more suitable to be used as damage index of SC-BSF structure than interstory displacement angle.The research in this paper can provide reference for the performance evaluation of earthquake-resistant structures with recoverable function considering aftershock,and has important theoretical and practical value.