Effects of rubber shear modulus variability on the seismic response of isolated bridges

The mechanical behavior of bridge decks equipped with High Damping Rubber Bearings is strongly affected by the rubber shear modulus that governs their lateral stiffness. It is a random variable, which can be described by a normal distribution. In this paper, the effects of the variability of the shear modulus are investigated in terms of displacements for both the isolators and the piers, with reference to a case-study RC bridge with continuous caisson deck over four spans. The bridge is modelled with minimal systems with a reduced number of degrees of freedom along the longitudinal and transversal directions. Linear time-history analyses have been carried out using 7 natural seismic records, by considering 10,000 samples for the shear modulus fitting the chosen distribution. A statistical analysis has been then developed on the numerical results in order to obtain percentile values. Finally, Upper and Lower Bounds are identified for design purposes.