Design criteria for Fiber Reinforced Rubber Bearings

This paper contains the findings of a study on the mechanical behaviour of unbonded Fiber-Reinforced Bearings (FRB). Typical FRBs consist of several layers of rubber that are bonded to fiber reinforcing sheets. The purpose of the reinforcement is to prevent the rubber from bulging laterally under compressive load. The most important aspects of these bearings are (i) they do not have thick end plates; (ii) they are not bonded to the top and bottom support surfaces; and (iii) their reinforcements are very flexible. These aspects may seem to be design deficiencies, but they have the advantage of eliminating the presence of tensile stresses in the bearing by allowing it to roll off the supports when it is sheared. This reduces the typical bonding requirements. The weight and the cost of isolators is reduced by using fiber reinforcing, no end-plates and no bonding to the support surfaces, offering a low-cost lightweight isolation system. The paper introduces simple theories, valid as design criteria, for the determination of the tensile stresses in the reinforcement, the vertical stiffness of the bearing, the ultimate lateral displacement. A good benchmark to test the theories is proposed in this work using the output of Finite Element Analysis (FEA).