An Integrated Framework for Selecting High-Strength Masonry Infill Retrofits in Nonductile RC Frames

This study investigates the seismic performance of a low-rise, nonductile reinforced concrete building retrofitted with high-strength masonry infill walls having a compressive strength of approximately 25 MPa. Three infill layouts were evaluated using nonlinear pushover analysis. A multi-criteria evaluation framework was then applied by considering stiffness, lateral strength, added weight, and a preliminary wall-volume-based cost indicator. The most favorable configuration was further assessed using Multiple Stripe Analysis, and system-level fragility curves were developed using PGA and Sa(T₁) as intensity measures. The results show that high-strength masonry infills substantially enhance the lateral capacity of the RC frame, with peak base-shear capacities increasing by approximately 3.6, 3.3, and 2.3 times for HBW1, HBW2, and HBW3, respectively. The multi-criteria evaluation identified HBW1 as the most favorable configuration. A preliminary stiffness–weight–strength relationship was also proposed as a screening tool; its evaluation against 11 independent building-scale cases showed reasonable consistency, with eight predictions within ±10% and all predictions within approximately ±15% of the literature-derived strength gains, and a mean absolute error of about 5.2%.