High damping rubber (HDR) bearings are extensively employed for seismic isolation of bridges or buildings. In HDR material, a filler is added to the natural rubber in order to improve some of its properties in terms of strength, stiffness, as well as dissipation capacity. The addition of the filler also induces a stress-softening behaviour under cyclic loadings related to the internal microstructure damage (Mullins effect). This phenomenon, which makes the response of HDR bearings strongly path-history dependent, may significantly influence the seismic response of isolated systems. The present work aims to study the consequences of such path-dependent behaviour in the seismic response of bridges isolated with HDR bearings. For this purpose, the response of a realistic bridge under different seismic inputs (far-field and near-fault ground motions) is analyzed by using for the bearings a process dependent rheological model and a simplified model in which the Mullins effect has exhausted. The comparison between the results obtained shows that neglecting the Mullins does not impact the estimate of the bearing maximum displacements, but it can results in a significant underestimation of the restoring force provided by HDR bearings, for both far-field or near-fault records.
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