Optimal retrofit selection for seismically-deficient RC buildings based on simplified performance assessment

This study deals with the selection of optimal retrofit solutions for seismically-deficient Reinforced Concrete (RC) buildings. To this aim, Multi-Criteria Decision-Making (MCDM) analysis is used. A discussion on the retrofit design strategy is first presented, recommending designing each retrofit solution for the same expected damage state under the design-level earthquake-induced ground-motion spectrum. Secondly, it is argued to explicitly consider seismic economic losses as a decision criterion. To this aim, seismic fragility/vulnerability relationships are derived for the structure of interest retrofitted with different techniques and considering a large suite of ground-motion records. Simplified-yet-accurate non-linear static procedures are used as an alternative to non-linear time-history analysis to reduce the challenges in building detailed numerical models, computational demand, and results interpretation. Specifically, three increasingly-refined structural analysis methods are adopted to derive fragility/vulnerability curves: the Simple Lateral Mechanism Analysis (SLaMA), which is an analytical approach; numerical pushover; and non-linear time-history analysis. A seismically-deficient RC school index building, with construction details typical of developing countries, is used for illustrative purposes. The case-study structure is retrofitted through concrete jacketing, addition of concrete walls, and addition of steel braces, all designed through Direct Displacement-Based Design. The MCDM analysis is performed adopting, among other criteria, intensity-based losses derived with the three considered analysis methods, using state-of-the-art, advanced ground-motion intensity measures. The results show that the ranking of the retrofit alternatives is rather insensitive to the adopted analysis method, even if the considered weight for the seismic loss criterion is relatively high (30{%} in this example). Findings from this study suggest that simplified analysis methods can be effectively employed in the preliminary/conceptual design of retrofit solutions for seismically-deficient buildings.