Quantifying damage in the steel shims of seismic isolation rubber bearings due to support rotation

Seismic isolation is an effective technique for mitigating the earthquake movements on important infrastructures such as bridges and hospitals. Rubber bearings are one of the most common seismic isolation devices used for the protection of critical infrastructure assets. Isolators are critical elements of an isolated structure, and as such, they should experience limited, if any, damage during earthquake shaking. Damage associated with yielding of the reinforcing steel shims in seismic isolation rubber bearings has received limited attention in the literature. This study investigates the effect of the steel reinforcement characteristics on the behavior of rubber bearings under combined axial load, shear displacement, and rotation. The potential damage of the steel shims and the rubber bearings under design-level lateral loads is investigated using a damage index, rpl, and a damage factor, Ω, respectively, with emphasis placed on the thickness of steel shims.