Modeling the compression stiffness degradation in circular elastomeric bearings due to fatigue

Laminated rubber, or elastomeric, bearings fatigue when subjected to repeated cycles of loading. Fatigue in these elements is characterized by the formation of cracks typically originating at the interface of the steel-rubber laminae at the outermost edge of the laminate then propagating at an inclination toward the center of the bearing under subsequent cycling. The presence of fatigue cracks alters the bulging surface of the rubber layers, thereby degrading the stiffness properties of the bearings. Past experimental studies have shown the stiffness degradation of laminated rubber bearings can be significant, i.e., reductions on the order of 20-30%. To date, much of the analytical and experimental research has been focused on the determination of the initiation of fatigue cracking to establish replacement schedules for elastomeric bearing components in aerospace and rail applications. However, in bridge applications elastomeric bearings are likely to fatigue while in service and the level of stiffness degradation could significantly affect the in-service performance and safety of the bridge. To develop an improved understanding of the impact of fatigue cracking on the stiffness degradation of elastomeric bearings, a modeling framework is proposed that builds on previous research to link cycles of loading to stiffness degradation. The modeling framework is implemented in a numerical routine to perform parametric and sensitivity studies to quantify the effect of parameters and factors variations on both the stiffness degradation and fatigue life of elastomeric bearings.