Influence of high damping natural rubber bearing model on the seismic response evaluation of isolated bridges

High damping natural rubber (HDNR) bearings are extensively employed in seismic isolation of both bridges and buildings. In HDNR material, a filler is added to the natural rubber to increase its stiffness and dissipation capacity. However, the addition of the filler induces also a stress-softening behaviour under cyclic loadings related to the internal microstructure breakdown or sometime referred to as damage. This phenomenon may significantly influence the seismic response of isolated systems given its recovery characteristics. The present work aims to study the consequences of such softening behaviour on the seismic performance of bridges isolated with HDNR bearings. For this purpose, the response of an isolated bridge pier under different seismic inputs is analyzed by pointing out the differences between the results obtained by considering two different conditions for the bearings, one assuming the "virgin" rubber properties and the other assuming the "stable" or "scragged" properties.