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What is the importance of shear stiffness in the design of elastomeric bearing?

Elastomeric bearings are made of layers of synthetic chloroprene rubber (CR) or natural rubber (NR). Steel plates are placed between rubber layers, rubber layer will be merged by vulcanization to produce a single pad. The elastomeric bearing will allow for rotation of superstructure. Movement of the superstructure will be accommodated through elastic deformation.
Figure 1

Elastomeric bearings are relatively stiff in compression. Elastomeric bearing deforms to accommodate structure movement and rotation due to various reasons such as thermal gradient, shrinkage, creep, and live loads. The elastomeric bearing should be flexible under shear deformation to allow smooth transfer of those movements. 

The elastomeric bearing should be designed in serviceability limit state. The cross-sectional area of elastomeric bearing is determined by the compression stress in the serviceability limit state. The shape factor also playing a significant rule of bearing capacity. Higher shape factor means higher capacity. The long side of bearing should be placed parallel to the axis of rotation so it will facilitate the rotation of bearing. The thickness of bearing should be determined in accordance with the allowable shear strain requirement. Shear strains should not exceed the permissible limit to avoid the rolling over of the structure or the fatigue failure. The vertical stiffness of bearing obtained by inserting the steel plates between the rubbers layers. Loads and rotations should be combined differently to check for uplifting. 


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