Effects of model configurations on the post-fire performance of lead-rubber bearings

Abstract

The study investigates how model configuration assumptions in heat-transfer modelling affect the thermal field and the post-fire mechanical performance of lead–rubber bearings (LRBs). Because prior studies generally model only the isolator while others include connection components, the authors address this gap by comparing three FE model configurations: A) isolator only, B) isolator+upper/lower steel flange plates, and C) isolator+flange plates+connected RC column. Thermal and mechanical analyses are performed in ANSYS Workbench. Fire exposure is defined using the ISO-834 standard fire curve with 20, 30, and 40 minutes of heating, resulting in nine scenarios (3 configurations×3 durations). Temperature-dependent degradation of rubber properties is incorporated in the thermo-mechanical phase; peak nodal temperatures from the thermal analysis are transferred as the initial thermal state for the structural model. Mechanical loading includes 10 MPa vertical compressive stress and lateral displacement corresponding to 100% shear strain. Results show that post-fire horizontal stiffness and strength degradation increase with fire duration and depend strongly on the model configuration. Configurations B and C exhibit a clear reduction in horizontal stiffness after fire exposure, while the isolator-only case (A) shows the smallest deviation from the pre-fire response. The inclusion of steel flange plates (B) leads to more pronounced degradation, consistent with intensified heat transfer into the isolator; adding the RC column (C) slightly moderates thermal transfer compared with B but still produces significant post-fire softening. Overall, the study highlights that neglecting flange plates and connected structural elements can underestimate internal temperature distribution and misrepresent post-fire performance, underscoring the need to include these components in FE modelling for realistic fire assessment.