In-Plane and Out-of-Plane Behaviour of RC Frames Reinforced with Lightweight Steel Exoskeletons

In light of recent seismic events and the growing emphasis on energy efficiency, retrofitting older buildings has become essential for ensuring both structural safety and sustainability. Many reinforced concrete (RC) buildings lack the resilience needed to withstand seismic forces, rendering them vulnerable to damage from both in-plane and out-of-plane actions. This study investigates a modular lightweight steel exoskeleton designed to enhance seismic performance while minimizing interior disruption. The system incorporates thermal improvements through integrated insulating panels and consists of cold-formed steel frames and X-bracing, which provide external reinforcement to RC frames. Using Abaqus CAE for finite element analysis, the study assessed both in-plane and out-of-plane behaviours of both the as-built RC frame and the Resisto 5.9-reinforced one. The in-plane pushover analysis revealed a significant improvement, with maximum increase of force by 690% and of initial stiffness by 379%. In the out-of-plane analysis, calibrated against laboratory tests, an 18% enhancement in ultimate force was observed, effectively preventing infill wall expulsion. These findings highlight the potential of lightweight steel exoskeletons as a robust and adaptable solution for upgrading RC buildings, ensuring enhanced seismic resilience while contributing to safer and more energy-efficient structures.