Sensitivity of 3D Base‐Isolated Buildings to Individual Isolator Variability

Variability in elastomeric isolators arises from differences in rubber formulation and curing, leading to noticeable changes in stiffness and damping among nominally identical bearings. While most previous studies have examined global isolator variability associated with environmental or aging effects, individual isolator variability has received relatively little attention. This study investigates the influence of isolator variability on the seismic response of three five‐story three‐dimensional reinforced concrete buildings with symmetric and asymmetric plan geometries under four variability scenarios: uniform, individual, batch, and eccentricity. The effective stiffness, K eff , and hysteresis area, W , of a high damping rubber bearing (HDRB) were used as scaling parameters to represent isolator variability, rather than bilinear or trilinear parameters such as characteristic and post‐yield stiffness. Twenty bidirectional ground motions were applied, and tolerance levels ranged from ±10% to ±50%. Results show that individual isolator variability produced negligible changes in global structural responses, as the decreased and increased isolator properties balanced out across the isolation system. However, the spatial distribution of isolator variability proved to be a critical factor. In particular, spatially correlated variability introduced stiffness eccentricities within the isolation layer, leading to amplified torsional response and increased response uncertainty. Variability up to ±30% caused only modest deviations in global response that remained within acceptable bounds, even in plans with significant inherent eccentricity. Accordingly, a tolerance of ±30% is recommended as a conservative upper limit, while ±50% may be considered acceptable for symmetric or slightly eccentric plans where torsional effects remain limited.