Seismic retrofit of rc buildings by using base isolation: Superstructure modelling issues

Existing reinforced concrete buildings are vulnerable to seismic actions due to the lack of proper seismic details. This is triggering for brittle failures, on beam-column joints or on columns, as commonly observed in the aftermath of recent seismic events. Furthermore, recent reconstruction processes re-marked that the majority of the repair costs concerns the non-structural components such as infills and partitions. In this context, the design of efficient retrofit solutions should aim at reducing the expected losses to structural and non-structural components. To this end, base isolation technique can signifi-cantly increase the seismic safety and reduce the expected losses. Although the base isolation is very efficient, in some cases a combination with other retrofit techniques is necessary to avoid local failures on the superstructure. The scope of this research is to investigate the effectiveness of the base isolation and the response of the superstructure through different numerical models. A push-over analysis is carried out to assess the seismic vulnerability and the weaknesses of the structure in the as-built configuration. Nonlinear time history analyses are carried out on the base isolated building, modelling the superstructure as linear and nonlinear, as well as in the bare and infilled configurations. The results are compared and discussed with reference to the inelastic demand on the superstructure and the need for further retrofit interventions combined with base-isolation.