Development of Fragility Curves for Reinforced-Masonry Structural Walls with Boundary Elements

Performance-based seismic design requires accurate damage/loss models for different seismic force resisting systems. Fragility functions are considered one of the most common damage/loss models that link specific demand parameter to the probability of exceedance of different damage states. Recently, reinforced masonry shear walls with boundary elements ($\mathrm{RMSW}+\mathrm{BEs}$) showed enhanced lateral performance and curvature ductility compared to that of rectangular walls. However, few experimental studies are available to date focusing on the seismic response of $\mathrm{RMSW}+\mathrm{BEs}$. FEMA guidelines provide fragility curves for reinforced masonry shear walls having only a rectangular cross section. Moreover, limited data are available to generate fragility curves for $\mathrm{RMSW}+\mathrm{BEs}$. In this paper, a numerical study is presented using the macromodeling approach embedded in the SeismoStruct software to simulate the in-plane lateral response of flexural dominated $\mathrm{RMSW}+\mathrm{BEs}$. The numerical model is validated against three $\mathrm{RMSW}+\mathrm{BEs}$ walls tested under quasi-static cyclic loading reported in the literature. Subsequently, a parametric study is performed on 36 $\mathrm{RMSW}+\mathrm{BEs}$ to evaluate the influence of varying the axial stress, wall aspect ratio, and vertical reinforcement ratio on the lateral response of the $\mathrm{RMSW}+\mathrm{BEs}$. It was observed that $\mathrm{RMSW}+\mathrm{BEs}$ strength increases as the aspect ratio decreases, vertical reinforcement ratio increases, and level of axial stress increases. On the other hand, decreasing the wall aspect ratio, vertical reinforcement ratio, and level of axial stress enhances the $\mathrm{RMSW}+\mathrm{BEs}$ displacement ductility. The drift ratios corresponding to three damage states (i.e., slight, moderate, and severe) were computed according to FEMA guidelines. Finally, fragility curves were generated for $\mathrm{RMSW}+\mathrm{BEs}$ utilizing the computed numerical data of the studied walls, which can be adopted in performance-based seismic design frameworks.