Abstract
Reinforced concrete (RC) frames with unreinforced masonry (URM) infill walls are widely distributed across high-seismicity regions globally. Although infill panels are often considered non-structural during design, their severe interaction with the surrounding boundary frame frequently triggers brittle shear failures in columns and premature soft-story mechanisms. This study investigates the seismic vulnerability and performance enhancement of sub-standard multi-story RC frames retrofitted with Fabric-Reinforced Cementitious Matrix (FRCM) composites. A nonlinear macro-element numerical framework, explicitly capturing in-plane and out-of-plane infill-frame interaction, shear-flexure column coupling, and FRCM-to-substrate debonding, was developed and validated against experimental cyclic tests. Incremental Dynamic Analyses (IDA) utilizing a suite of thirty spectrum-compatible earthquake ground motions were conducted on four-story and eight-story prototype frames in both bare, unretrofitted infilled, and FRCM-retrofitted configurations. Derivation of analytical fragility curves demonstrated that application of FRCM jackets to infill panels and beam-column joints reduces the probability of reaching Extensive and Complete damage states by 58% and 64%, respectively, at Maximum Considered Earthquake (MCE) intensity levels. The composite intervention successfully shifted the failure mechanism from localized brittle shear failure to distributed flexural yielding, validating FRCM as a sustainable and highly effective seismic strengthening solution for existing RC infrastructure.
