Effect of Loading Directionality on the Horizontal Stiffness of Unbonded Scrap Tire Rubber Pad Isolator

The horizontal stiffness of a low-cost base isolator made with scrap tire rubber pad (STRP) is investigated. A finite element approach is used for modeling, verification, and analyses for the STRP isolator. The isolator is assumed to be utilized without any mechanical fastening with the structure, which transfers lateral load through friction between the isolator and the structure. The effect of the loading directionalities and the coupling between the orthogonal lateral displacements are taken into consideration. It was found that the directionality of the input displacement reduces the horizontal stiffness, and its effect is high for a high length-to-width ratio of the isolator. The lateral stiffness is overestimated when coupling between lateral displacements is ignored, and this overestimation is high for a high length-to-width ratio of the isolator.