Seismic reliability of structures equipped with frictional isolators with improved lateral impact behavior

A novel frictional device to achieve seismic isolation, the Lateral Impact Resilient Double Concave Friction Pendulum (LIR-DCFP), has been suggested as an alternative to mitigate the adverse effects of internal lateral impacts. These impacts between the inner slider and the restraining rims of the concave plates can produce the failure of the bearing and a dramatic increment in the ductility demand of the superstructure. The LIR-DCFP has an improved inner slider with an internal gap capable of limiting the magnitude of the impact and dissipating a critical amount of energy during the impact. This work presents a reliability-based comparison of the seismic performance of structures isolated through LIR-DCFP devices or classical Double Concave Friction Pendulum (DCFP) bearings. The response of the superstructure was represented using a simplified elastoplastic model considering hardening and softening post-yield behaviors. The isolation system was represented using models based on rigid body dynamics, including the lateral impact behavior. A parametric analysis was performed, including a wide range of structural properties, two types of frictional isolators, and considering the friction coefficients as relevant random variables. The aleatory uncertainties of the seismic input were included by selecting different sets of natural records matching the conditional spectra of a site in Riverside (California). Incremental Dynamic Analyses were conducted to characterize the statistics of the maximum ductility demand of the superstructure and determine the probabilities exceeding limit state thresholds, (i.e., the fragility curves). Finally, using the seismic hazard curves, the seismic reliability was determined. For increasing values of the internal gap, better seismic performance is achieved compared to the performance obtained employing DCFP devices. This better performance is improved if the superstructure is designed to remain in its elastic range if the internal impact is not produced. Reductions up to 19% in the probabilities exceeding limit state thresholds in terms of maximum ductility demand in a time frame of 50 years are possible by replacing classical DCFP bearings with LIR-DCFP isolators.