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
