Life-cycle cost optimization of the seismic retrofit of existing RC structures

The life-cycle cost analysis of buildings prone to seismic risk is a critical issue in structural engineering. Expected loss, including damage and repair costs, is an important parameter for structural design. The combination of economic theory and computer technology allows for a more developed approach to the design and construction of structures than ever before. In this study, a simplified method based on a semi-probabilistic methodology is developed to evaluate the economic performance of a building prone to seismic risk. The proposed approach aims to identify the most cost-effective strengthening strategies and strengthening levels for existing structures during their structural lifetime. To achieve this, the method identifies the optimal strengthening level, computing on the one hand the costs of strengthening the structure at different performance levels for each strategy, and, on the other, the expected seismic loss during the structure’s lifetime. To assess the expected loss, the building is divided into several components, both structural and non-structural. A set of fragility curves is assigned for each component. Then, once the structural model and the various components of the building, with the corresponding fragility curves, are defined, a loss assessment is performed using a static non-linear analysis. The summation of the strengthening costs and the discounted expected losses produces a relationship between the total costs and the strengthening level. The minimum of this relationship identifies the most cost-effective strengthening intervention. As a case study, this method is applied to an existing reinforced concrete (RC) structure severely damaged by the 2009 earthquake in L’Aquila. Different strategies are analyzed, namely the FRP (fiber reinforced polymer) strengthening of elements, the RC jacketing of columns, RC exterior shear wall insertions, and the base isolation of the building.