Enhancing out-of-plane seismic resistance of masonry walls with fiber-reinforced overlays: tests, modeling, and fragility analysis

This study investigates the out-of-plane seismic performance and fragility of masonry walls retrofitted with basalt fiber grid (BFG), carbon fiber–reinforced polymer (CFRP), glass fiber–reinforced polymer (GFRP), and ultra-high-performance concrete (UHPC). Large-scale masonry wall specimens were tested under lateral loading to examine strength, deformation capacity, and failure mechanisms. This study focuses on the pure out-of-plane response of masonry walls, without considering in-plane forces or deformations. All retrofitted walls significantly outperformed the unreinforced masonry (URM) wall, which failed at 11.34 kN. Peak strengths reached 40.79 kN (GFRP), 30.92 kN (UHPC), 24.88 kN (BFG), and 21.39 kN (CFRP), with varying ductility and crack patterns. Discrete finite element models, calibrated against experimental results, were employed to perform incremental dynamic analysis and derive seismic fragility curves. Results show that retrofitting markedly reduced failure probabilities, raising median spectral acceleration thresholds by factors of 3–7 compared with URM. Among the methods, GFRP achieved the most favorable fragility performance, exhibiting both high capacity and low drift exceedance. These findings demonstrate that retrofit material choice and configuration are critical for improving seismic resilience and reducing collapse risk in masonry structures.