Fragility-informed selection of bridge retrofit scheme based on performance criteria

Bridge damage due to earthquakes and the subsequent direct and indirect losses lead to the incorporation of seismic design and retrofitting into recent design codes worldwide. Therefore, several retrofit schemes were introduced for the enhancement of the seismic performance concerning both the superstructure and substructure. The aim of the present paper is to propose a framework for fragility-informed selection of retrofit schemes for specific performance criteria, based on fragility curves of as-built and retrofitted bridges. The concepts of fragility-informed retrofitting (FIR) and performance-based retrofitting (PBR) are introduced, focusing on the criteria for selecting a quasi-optimum retrofit scheme, rather than a priori adopting one. The methodology recently proposed by the authors for bridge-specific fragility curves of as-built bridges is extended herein for bridges retrofitted with various retrofit schemes. In the frame of the methodology, efficient and reliable estimation of retrofitted component capacity and demand is performed considering different failure modes, while the critical component fragility is considered in selecting the retrofit scheme. Empirical relationships for the calculation of component-specific capacity, namely limit state thresholds in terms of displacement, are proposed for piers retrofitted with different methods (RC and FRP jackets). An equivalent efficiency criterion is introduced for the selection of properties of different retrofit schemes in order to set a basis for comparison and selection of a quasi-optimum scheme. The effectiveness of various retrofit strategies, i.e. pier strengthening considering two alternative strengthening schemes (RC and FRP jackets) and isolation is evaluated by applying them to a monolithic and a bearing-supported bridge, respectively.