In Civil Engineering ( Bridge works), How to determine the size of elastomeric bearings?

For elastomeric bearing, the vertical load is resisted by its compression while shear resistance of the bearing controls the horizontal movements. The design of elastomeric bearings are based on striking a balance between the provision of sufficient stiffness to resist high compressive force and the flexibility to allow for translation and rotation movement.

The cross sectional area is normally determined by the allowable pressure on the bearing support. Sometimes, the plan area of bearings is controlled by the maximum allowable compressive stress arising from the consideration of delamination of elastomer from steel plates. In addition, the size of elastomeric bearings is also influenced by considering the separation between the structure and the edge of bearing which may occur in rotation because tensile stresses deriving from separation may cause delamination. The thickness of bearings is designed based on the limitation of its horizontal stiffness and is controlled by movement requirements. The shear strain should be less than a certain limit to avoid the occurrence of rolling over and fatigue damage. The vertical stiffness of bearings is obtained by inserting sufficient number of steel plates.  

That's a nice question. First determine all the loads the bearing needs to pick up, that's is vertical but also horizontal! and that is the biggest problem. But if you have the loads complete it becomes simple

Determine the size of elastomeric bearing  loaded > so need vertical resist to force flexibility to allow for rotation & translation movement