Fragility Analysis For Vertical Irregular Reinforced Concrete Frame Structures Subjected To Pulse-like Ground Motions

Seismic fragility analysis is one of effective methods for the evaluation of structural seismic hazard. The characteristics of earthquake damage can be described by seismic fragility cures, which is the conditional probability of the response exceeding the bearing capacity of the structure under the different strong earthquake. Aiming at the deficiency of quantitative description in seismic design philosophy, this paper studies the seismic displacement response demand of the reinforced concrete (RC) frame structure with vertical irregularities subjected to velocity pulse-like ground motions, and analyzes the probability of seismic displacement demand exceeding displacement capacity. The main research contents and conclusions are as following.1. Seismic displacement demands of vertical irregular RC frame structures subjected to velocity pulse-like and no velocity pulse-like ground motions are compared by nonlinear dynamic time history analysis. The results show that seismic displacement demands of vertical irregular structures are obviously different under pulse-like and non pulse-like ground motions, and the former is greater.2. The influence of mass irregularity or stiffness irregularity on seismic displacement demand of RC frame structures are investigated by nonlinear dynamic time history analysis under the different strong earthquake. The results demonstrate that mass and stiffness discontinuity have importance influence on structural seismic displacement response, and seismic displacement demands increase with increasing ground intensity. The variation of the top mass and lower stiffness variation have relatively higher influence on structural displacement demand.3. Employing five- and ten-storey vertical irregular and regular frame structure and considering the uncertainty of input ground motion, the maximum inter-story displacement demands are analyzed by nonlinear dynamic time history analysis. The probability of seismic displacement demand exceeding displacement capacity is studied, and seismic fragility cures are obtained by nonlinear regression analysis. The results show that strength and stiffness irregularities have important influence on the structural inter-story drift under the different strong velocity pulse-like ground motions, and peak inter-story drift of first storey increase with increasing the degree of irregularity, but peak inter-story drift of middle storey decrease. The dispersion of peak inter-story drift increases with increasing ground motions intensity. Strength and stiffness irregularities also have significant influence on seismic fragility curve, and the changing trend of fragility curve is different owing to as number of story varies.