Revaluation of the aging property modification factor of lead rubber bearings based on accelerated aging tests and finite element analysis

The hysteresis characteristics of lead rubber bearings (LRBs) are affected by external temperature and aged-related degradation, among other things. The American Association of State Highway and Transportation Officials (AASHTO) presents an aging property modification factor (lambda(aging)) according to the type of seismic isolators in order to consider the change at design stage, of the age-related degradation characteristics of LRBs. However, the aging property modification factor is affected by the diameter of a bearing and the aging time as well as the type of seismic isolators. In this study, the time dependent properties of rubber materials were defined based on the results of an accelerated aging test, and the critical aging depth of the LRBs was calculated from the aging depth test results. The hysteresis characteristic of LRBs was analysed using the finite element method. From the analysis results, it was found that post yield stiffness and effective stiffness of small LRBs was higher than that of large LRBs. Therefore, it is necessary to present the existing aging property modification factor of LRBs (including rubber bearings) according to the size of the seismic isolators.