The size of the lead plug is proportional to the yield strength of the isolator. The post-yielding stiffness is proportional to the rubber bearing stiffness, and increases with the plan size of the rubber bearing and reductions in the isolator height. The capability of a lead plug to dissipate energy is proportional to the plastic displacements. Good fatigue properties for plastic cycles. During severe seismic attacks, however, the lead plug is capable of deforming through many low-cycle plastic deformations without a loss of strength occuring.
Experimental studies indicate that lead responds essentially with elastic-perfectly plastic loops.
Hence, for practical purposes the post-yielding isolator stiffness is equal to the stiffness of the rubber bearing alone. Geometry and Material Properties Figure 2 is a plan and elevation view of the lead-rubber laminated bearing we will consider in the analysis. See Figure 3. Elevation Views of Finite Element Mesh Flexural Behavior Figure 4 is a plan view of a lead-rubber isolator, showing the section dimensions and positions of the fiber elements. The fibers are positioned at the centroid of the material quadrant.