Development of Fragility Curves for RC Columns Retrofitted with FRP Jackets

Abstract

New probabilistic performance-based seismic design and assessment methods, such as the FEMA P-58 framework, employ fragility curves to evaluate damage in structural and non-structural components for a given level of shaking intensity or structural demand. Damage fragility curves in FEMA-P58 define the conditional probability of reaching or exceeding a specific damage state for a given demand parameter (such as the story drift) obtained from structural analysis. While default fragility parameters are provided in this framework for conventional structural components in buildings, no specific guidelines are given for retrofitted elements such as jacketed columns. This paper proposes new damage fragility curves for circular RC columns retrofitted with fiber reinforced polymer (FRP) jackets. A database of 51 tests on FRP-retrofitted columns subjected to lateral loading was compiled from the literature to study the damageability of these elements. Three damage limit states were defined: yielding of vertical reinforcement (low damage), cracking/discoloration of FRP (moderate damage), and FRP failure (severe damage). Fragility curves were developed for these three damage states adjusting lognormal functions to experimental data and using drift ratio as demand parameter. The fragility functions present median drift ratios of 0.6%, 2.9% and 9.0% for the low, moderate and severe damage limit states, respectively. Given the dispersion of the functions, the 5% probability of exceedance for low, moderate and severe damage corresponds to drift ratios of 0.25%, 1.5% and 4.9%, respectively.