Simplified framework for economic convenience of base isolation as seismic retrofit solution for existing RC buildings

Abstract

Modern seismic retrofit strategies aim at increasing the building safety under high intensity earthquakes and minimizing the possible damage and, in turn the expected economic losses (EAL) under frequent and low intensity earthquakes. Classic techniques based on tradition or innovative material such as steel jacketing or FRP wrapping aims at increasing the strength/ductility of reinforced concrete (RC) members, but they do not significantly act in reducing the engineering demand parameters EDPs such as acceleration and drift. On the other side innovative techniques such as base isolation are capable of combining the increase of seismic safety with the significant reduction of acceleration and drift demand on the superstructure, thus, resulting in a significant reduction of the EALs. Although the number of applications is significantly increasing in Italy, its wide use is discouraged by the high cost of installation. Considering the annual savings related to the reduction of the EALs, the payback time (PBT) of the economic investment in a retrofitting by using base isolation can be comparable to that of other techniques. However simple tools to easily assess the PBT knowing major building characteristics are currently not available.This paper proposes a novel framework to estimate the EALs and the PBT of RC buildings retrofitted by means of FRP or Base Isolation based on the main building characteristics (i.e. in-plane geometry, number of floors, seismic). It is implemented in a MATLAB code to perform NLTHs on simplified structural models and calculate the EALs by using the full PBEE framework and considering the uncertainties in the hazard, damage and loss analysis. The framework is validated against the results of a case study building analyzed by means of a refined 3D FEM model and calculating the EAL by means of the FEMA P-58 approach. A parametric study is carried out varying the concrete compressive strength and the reinforcement details to check the sensitivity of the framework to these variables. The preliminary results are presented and discussed.