2015 CSCE Annual Conference Regina - Building on our Growth Opportunities Conference
Dr. Shahria Alam, University of British Columbia
Seismic isolation bearings are intended to lengthen superstructure’s vibration period by their low lateral stiffness. Their vertical stiffness, however, should remain in a safe range in order to withstand gravity loads imposed by the superstructure. Part of the bearing’s vertical load-carrying capacity is provided by closely-spaced internal steel shims and the rubber, as an incompressible material, bonded to the steel reinforcements. As the bearing undergoes lateral deformations, its vertical stiffness and, as a result, its load-carrying capacity, tends to decrease, which might have catastrophic consequences. In this research, the vertical stiffness of rectangular rubber bearings is studied. The effect of lateral deformations on the vertical stiffness is investigated through three methods: 1) The two-spring method, 2) Overlapping area method and 3) Linear interpolation method. The effect of manufacturing central holes is also investigated and found not to be considerable to be taken into account. The effect of lead core in lead-core rubber bearing isolators is also studied and found to be the dominant factor in determining the vertical stiffness. It is observed that, unlike the two-spring method, the two other methods suggest a linear trend for vertical stiffness reduction in bearings with a rectangular cross section. It is also shown that the overlapping area method suggests a steeper decrease and gives the most conservative prediction of the vertical stiffness.