Seismic resistance of a reinforced concrete building retrofitted via base isolation

This paper deals with the evaluation of the seismic resistance of a reinforced concrete building that originally was not designed to resist earthquake loading and afterwards was subjected to a seismic retrofitting that included both a partial reinforcement of the existing structure and a base isolation system. The seismic performance of the retrofitted building has been evaluated with reference to the collapse conditions. To this aim 3-D nonlinear static analyses have been performed and a procedure for the definition of simplified two-degrees-offreedom nonlinear systems, equivalent to the base isolated building, has been assessed. The equivalent simplified systems allowed us to perform a wide number of nonlinear dynamical analyses with reference to several seismic inputs characterized by different levels of peak ground acceleration. The ultimate capacity of the retrofitted building has been conventionally expressed in terms of the minimum PGA that causes the collapse of the building according to a prescribed design spectral shape.