Summary The paper deals with the seismic reliability of elastic structural systems equipped with friction pendulum isolators (friction pendulum system). The behavior of these systems is analyzed by employing a two‐degree‐of‐freedom model accounting for the superstructure flexibility, whereas the friction pendulum system device behavior is described by adopting a widespread model that considers the variation of the friction coefficient with the velocity. With reference to medium soil condition, the uncertainty in the seismic inputs is taken into account by considering a set of artificial records, obtained through Monte Carlo simulations within the power spectral density method, with different frequency contents and characteristics depending on the soil dynamic parameters and scaled to increasing intensity levels. The sliding friction coefficient at large velocity is also considered as random variable modeled through a uniform probability density function. Incremental dynamic analyses are developed in order to evaluate the probabilities exceeding different limit states related to both r.c. superstructure and isolation level defining the seismic fragility curves through an extensive parametric study carried out for different structural system properties. Finally, considering the seismic hazard curves related to a site near L'Aquila (Italy), the seismic reliability of the r.c. superstructure systems is evaluated, and seismic reliability‐based design abacuses are derived with the aim to define the radius in plan of the friction pendulum devices in function of the structural properties and reliability level expected. Copyright © 2016 John Wiley & Sons, Ltd.

The study analyzes the influence of double concave friction pendulum (DCFP) isolator properties on the seismic performance of isolated multispan continuous deck bridges. The behavior of these systems is analyzed by employing an eight‐degree‐of‐freedom model accounting for the pier flexibility in addition to the rigid presence of both abutment and deck, whereas the DCFP isolator behavior is described combining two single FP devices in series. The uncertainty in the seismic input is taken into account by considering a set of nonfrequent natural records with different characteristics. The variation of the statistics of the response parameters relevant to the seismic performance of the isolated bridges is investigated through the proposal of a nondimensionalization of the motion equations, with respect to the seismic intensity, within an extensive parametric study carried out for different isolator and bridge properties. Moreover, two cases related to different ratios between the sliding friction coefficients of the two surfaces of the DCFP devices are analyzed with the aim also to evaluate the corresponding optimal values able to minimize the seismic demand to the pier. In this way, all the presented nondimensional results are useful for the preliminary design or retrofit of multispan continuous deck bridges, isolated with DCFP devices, located in any site and in relation, especially, to the seismic ultimate limit states.

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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.

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