Mechanical behavior of the high-hardness damping rubber block in a composite seismic isolation bearing for cold-formed steel pallet racks

Cold-formed steel pallet racks are vulnerable to cargo loss and structural instability during earthquakes, particularly in the cross-aisle direction. To reduce the seismic response of the pallet racks, a high-hardness damping rubber block (HHDRB) was developed to provide horizontal restoring force and energy dissipation in a composite seismic isolation system without carrying vertical gravity loads. Thirteen specimens were tested under axial compression, monotonic shear, constant- and variable-amplitude cyclic shear, variable-frequency cyclic shear, and repeated-cycle loading. The experimental results showed that the ultimate shear strain reached 293.3% under monotonic loading, while the mechanical indices generally increased with increasing frequency over the tested range of 0.01–0.09 Hz. The 50-cycle test showed initial softening followed by slower stiffness degradation, with no visible specimen damage. Based on the experimental response, a two-parameter Mooney-Rivlin model combined with Prony-series viscoelasticity was calibrated over the range γ ≤ 150%. The finite element (FE) model reproduced the response at 100% shear strain with a maximum absolute relative error of 5.36% among the reported mechanical indices. Subsequent dimensional parametric analysis was used to establish generalized nonlinear equations relating component geometry to the initial stiffness and horizontal equivalent stiffness. The research findings provide a basis for HHDRB component selection and preliminary parameter design.