Seismic reliability of bridges isolated with FPS

The present analysis deals with the seismic reliability of isolated multi-span continuous deck bridges considering as the main aleatory uncertainties relevant to the problem the sliding friction coefficient of the friction pendulum (FP) isolators together with the seismic records characteristics. A six-degree-of-freedom model is defined to simulate the elastic response of the reinforced concrete pier, the infinitely rigid response of the deck supported by the seismic devices and the non-linear velocity-dependent behavior of the FPS bearings. The reinforced concrete abutment is modelled as a rigid support above which a FPS device is located. A set of natural records with different characteristics is properly selected and scaled to increasing intensity levels. The randomness on the friction coefficient is described by an appropriate probability density function to sample. For different system and isolator properties, fragility curves of both the reinforced concrete pier and FP devices supporting the deck are estimated. In accordance with the hazard curve of the design site, the seismic reliability curves are derived by means of the convolution integral.