Abstract
The effect of aftershocks on the fragility of single-story masonry structures is investigated using probabilistic seismic demand analysis Finite element models of an unreinforced masonry (URM) structure and a confined masonry (CM) structure are established and their seismic response characteristics when subjected to mainshock, aftershock, and the mainshock-aftershock sequence are then comparatively investigated. The effects of aftershocks and the use of confining members on the seismic response are studied. Probabilistic seismic demand models of the structures are built, and fragility curves under various conditions are derived to investigate the effect of aftershocks on structural fragility. The maximum roof displacement and maximum inter-story drift ratio are lower in the confined masonry model than in the unreinforced masonry model; additionally, the probability of exceedance (PE) values of each damage limit state reduced, and those of the mainshock-damaged models subjected to aftershock significantly increase compared to those directly subjected to a same-intensity aftershock. The probability of severe damage or collapse compared with the mainshock-damaged CM model is greater than when each is subjected to a same intensity aftershock. The use of confining members benefits aftershock resistance and reduces the failure probability of the mainshock-damaged structure. The PE values significantly increase with the aftershock scaling factor δ. Therefore, the effect of aftershocks should be considered in the seismic design and analysis of masonry structures.
Highlights
Strong earthquakes are often accompanied by aftershocks, and large numbers of aftershocks have been recorded in multiple earthquakes [1,2,3,4]
The fragility curve of the confined masonry (CM) model corresponding to each damage limit state is notably below that of the unreinforced masonry (URM) model
Taking the case of the aftershock scaling factor δ 1 as an example, Figure 11 shows the effect of confining members on the fragility curves of the mainshock-damaged URM and CM models subjected to aftershocks
Summary
Strong earthquakes are often accompanied by aftershocks, and large numbers of aftershocks have been recorded in multiple earthquakes [1,2,3,4]. Masonry structures in rural areas are typically not designed properly, and many self-built houses lack the necessary confining members, so these masonry structures have poor seismic performance To address this problem, taking a typical single-story masonry structure of the rural areas of Northeast China as an example, the present study builds finite element models of unreinforced masonry (URM) structure and confined masonry (CM) structural models, investigates the seismic responses and fragility of masonry structures subjected to mainshock, aftershock and mainshockaftershock sequence using nonlinear dynamic time history analysis and PSDA, and comparatively analyzes the effects of confining members such as ring beams and confined boundary columns on the seismic response and fragility of masonry structures. The maximum ISDA (ISDAmax) and the peak ground acceleration (PGA) are selected as the EDP and the IM, respectively, for the PSD analysis of the FIGURE 8 | Probabilistic seismic demand model of URM subjected to aftershock.
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