Risk Assessment of Reinforced Concrete Buildings with Rubber Isolation Systems Designed by the Italian Seismic Code

This paper presents an insight on the seismic response and seismic risk of base-isolated structures performed within the RINTC project, considering different configurations of rubber-based isolation systems. This represents an in-depth revision of past works due to the adoption of more robust and accurate isolator model. Four archetype 6-storeys RC frame buildings are examined, representing both new designed isolated buildings and existing buildings retrofitted with seismic isolation, differing in age of construction and location (the cities of L'Aquila (central Italy) and Naples (southern Italy)). All the isolation systems are designed in accordance with the current Italian Seismic Code. Seismic performance assessment is performed by multi-stripe nonlinear time history analysis. The annual failure rates for two different performance levels, namely Global Collapse and Usability Preventing Damage, are computed. The results point out that all isolation systems work effectively in limiting damage while they show a quite low margin with respect to collapse, regardless of the dominant failure mode, which is governed by the more fragile component among isolation system and superstructure. The annual failure rates derived for base-isolated buildings are critically reviewed and then compared with those obtained for similar new designed fixed-base RC buildings.