Why are steel plates inserted inside bearings in elastomeric bearings?

For elastomeric bearing to function as a soft spring, the bearing should be allowed for bulging laterally and the compression stiffness can be increased by limiting the amount of lateral bulging. To increase the compression stiffness of elastomeric bearings, metal plates are inserted.

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In order to make a elastomeric bearing act/ function as a soft spring it should be made to allow it to bulge laterally and also the stiffness compression can be increased by simply increasing the limiting amount of the lateral bulging. In many cases in order to increase the compression stiffness of the bearing the usage of metal plates is made. Once steel plates are included in the bearings the freedom of the bulge is restricted dramatically, also the deflection of the bearing is reduced as compared to a bearing without the presence of steel plates. The tensile stresses of the bearings are induced into the steel plates. But the presence of the metal plates does not affect the shear stiffness of the bearings.

Steel plates are inserted inside elastomeric bearings to provide reinforcement (or axial stiffness) against expansion due to poisson's effect in their plane, which effectively increases the bearing's capacity and durability under long term compressive forces.

An example of increased strength due to confinement between steel plates is the increased compressive strength given by 150mm cube of concrete as against 300mm long cylinder.

This is achieved by laminating the steel plates in multiple layers within the elastomeric bearing.

steel plates are there to cope with the tensile forces so that the lateral bulging of the bearings is limited. They increase the compressive stiffness of the bearing.