Seismic fragility analysis of masonry structures considering the effect of mainshock-aftershock sequences

•A simplified nonlinear static analytical method for seismic fragility analysis of masonry structures is developed.•Influence of aftershock’s PGA is studied by scaling it to various intensity levels.•Effects of mortar strength and the number of storeys are studied.•Effect of RC tie column on seismic performance of masonry structure is investigated. Earthquake investigations indicate that strong aftershocks can further aggravate the structural damage and low attention has been given to understand the seismic performance of masonry structures under seismic sequences. This manuscript studies the seismic fragility of masonry structures considering the effect of aftershocks by proposing a simplified probabilistic approach. In total, 36,000,000 stochastic earthquake-structure samples were generated using Monte Carlo simulation to consider the uncertainty of earthquake ground motions and structures, while seismic fragility curves of masonry structures were obtained by considering the following parameters: 1) aftershock intensity, 2) seismic wall area ratio, 3) site conditions, 4) the number of storeys, 5) reinforced concrete (RC) tie column, 6) mortar strength. The interstorey drift ratio was employed to assess the structural performance levels. The results showed that strong aftershocks have a significant influence on the fragility curves of masonry structures. The probability of exceeding the collapse limit state of structures can increase by 32.2% due to aftershock effect. Among the examined parameters it was found that the number of storeys has the greatest effect on the seismic fragility of masonry structures. By increasing the number of storeys, the probability of exceedance of the collapse damage state can increase up to 28.7%. The derived fragility curves are validated against a finite element method, which indicate the rationality of the proposed methodology.