Dissipative steel exoskeletons for seismic retrofit of RC buildings

This paper addresses the seismic retrofitting of highly vulnerable reinforced concrete (RC) buildings, with a focus on relevant and strategic structures such as schools, public offices, and cultural institutions. It proposes innovative retrofit solutions using external additive structures, or exoskeletons, designed for rapid, low-impact, and reversible interventions. These exoskeletons can be installed while the building remains operational, removed, replaced if damaged, and integrated with energy-efficient upgrades, reducing the time and cost of separate interventions. The research investigates two retrofit strategies for a school building: parallel exoskeletons with eccentrically braced frames (EBFs) and steel slit dampers (SSDs), and orthogonal exoskeletons with concentrically braced frames (CBFs) and shape memory alloy dampers (SMADs). A displacement-based design methodology ensures optimal energy dissipation and prevents premature buckling. Nonlinear time-history analyses validate the effectiveness of the retrofits across various earthquake scenarios. Peak inter-story drift ratio (IDR) responses are significantly reduced, remaining below the 2% collapse prevention limit. The parallel exoskeleton achieves IDR values of 0.66% and 0.86% in the X- and Y-directions, while the orthogonal exoskeleton records 0.63% and 1.06%, respectively. Additionally, the self-centering capability of SMA braces minimizes residual inter-story drifts, with permanent drifts as low as 0.0321% in the X-direction and 0.0090% in the Y-direction, ensuring repairability even after severe seismic events. These findings highlight the efficacy of dissipative exoskeletons in enhancing structural resilience while maintaining practicality and cost-efficiency for retrofitting critical infrastructure in earthquake-prone regions.