The Effect of Slip on the Compressive Behavior of Unbonded Rubber Pads: a Finite Element Approach

Steel-reinforced elastomeric isolators (SREIs) are considerably more expensive than unbonded steel-reinforced elastomeric bearings like those typically used in bridge applications to accommodate thermal expansion/contraction of the bridge deck. SREIs are vulcanized to thick steel end-plates (25 mm or thicker) that are bolted to the supports, while unbonded elastomeric bearings do not have thick end-plates, and they rely on friction to transfer the shear force between the bearing and the supports. The reason for the increased cost of SREIs is not merely the additional steel but the manufacturing cost associated with ensuring a proper bond between the steel plates and the rubber that will accommodate the large tensile stresses that can develop in SREIs during shearing of the isolator. Unbonded rubber bearings, on the other hand, are not bonded to their supports and do not develop tensile stresses during shearing. Consequently the need for stringent bonding requirements, such as those in SREIs, is eliminated. Since unbonded rubber bearings are held in place only by friction, there is a possibility that the frictional resistance may be compromised by lubrication that is introduced intentionally or accidentally. As a result a reduction in the frictional resistance that develops between the support-rubber interfaces is expected to occur. Since friction plays a dominant role in holding unbonded bearings in place, it is important to predict the effect of slip in these bearings. In this paper, the effect of parameters such as shape factor, friction coefficient and elastomer bulk modulus, on the pressure distribution and compression modulus of unbonded strip pads is investigated using Finite Element Analysis (FEA). It is shown that friction has a significant effect on both the maximum pressure and the compression modulus. 1 PhD Student, Dept. of Civil Engineering, McMaster University, Hamilton, ON, L8S 4L8 Assistant Professor, Dept. of Civil Engineering, McMaster University, Hamilton, ON, L8S 4L8 Rastgoo Moghadam S, Konstantinidis D. The effect of slip on the compressive behavior of unbonded rubber pads: a Finite Element approach. Proceedings of the 10 National Conference in Earthquake Engineering, Earthquake Engineering Research Institute, Anchorage, AK, 2014. The Effect of Slip on the Compressive Behavior of Unbonded Rubber Pads: A Finite Element Approach S. Rastgoo Moghadam and D. Konstantinidis