Probabilistic seismic response and reliability assessment of isolated
bridges
Giuseppe Carlo Marano
Department of
Environmental Engineering and Sustainable Development, Technical University of
Bari, Taranto, Italy
Abstract: Bridge seismic isolation strategy is
based on the reduction of shear forces transmitted from the superstructure to
the piers by two means: shifting natural period and earthquake input energy
reduction by dissipation concentrated in protection devices. In this paper, a
stochastic analysis of a simple isolated bridge model for different bridge and
device parameters is conducted to assess the efficiency of this seismic
protection strategy. To achieve this aim, a simple nonlinear softening
constitutive law is adopted to model a wide range of isolation devices,
characterized by only three essential mechanical parameters. As a consequence of
the random nature of seismic motion, a probabilistic analysis is carried out and
the time modulated Kanai-Tajimi stochastic process is adopted to represent the
seismic action. The response covariance in the state space is obtained by
solving the Lyapunov equation for a stochastic linearized system. After a
sensitivity analysis, the failure probability referred to extreme displacement
and the mean value of dissipated energy are assessed by using the introduced
stochastic indices of seismic bridge protection efficiency. A parametric
analysis for protective devices with different mechanical parameters is
developed for a proper selection of parameters of isolation devices under
different situations.
Keywords: bridge; seismic isolation; stochastic
analysis; nonlinear softening constitutive law; reliability assessment
