Indicators of improvements in seismic performance possible through retrofit of reinforced concrete frame buildings

Abstract

Retrofitting older reinforced concrete (RC) frame buildings aims to mitigate the well-established seismic vulnerabilities of these structures. However, the impact of retrofit design decisions (e.g. increases in strength, stiffness, or deformation capacity) on global performance is unclear because capacity and fragility models for retrofit structures are rare. This study quantifies the benefits of retrofitting nonductile RC moment frames in terms of global performance metrics, such as collapse rates and economic losses. In total, 27 buildings are assessed. In doing so, it subsequently identifies structural indicators, that is, strength and deformation characteristics of the retrofit system, which are most associated with improved performance. If the performance measure of interest is collapse risk and life safety, increases to either system strength or deformation capacity are important. If the performance measure of interest is expected earthquake-induced repair costs or economic losses, strength-based indicators are most effective. Some retrofits can significantly improve collapse risk without reducing economic losses.