Mechanical Properties and Seismic Loss Assessment of Improved Isolation Bearing with Variable Stiffness

For improving the seismic isolation effect, traditional rubber isolation bearing provides a smaller horizontal stiffness. However, it is unfavorable for the displacement control of the seismic isolation layer under rare earthquakes. In this paper, an improved lead-core rubber isolation bearing is proposed. The improved isolation bearing can provide a small horizontal stiffness to enhance the seismic isolation effect under small earthquakes. Under large earthquakes, it can provide a large horizontal stiffness to prevent over-limit failure due to excessive displacement. The mechanical properties of the improved isolation bearing were investigated using the finite element method (FEM), and the restoring force model of the improved isolation bearing was established. Based on the FEMA P-58 theory, the earthquake loss assessment in terms of repair cost and casualty indexes was carried out for normal frame structures, normal isolation structures, and improved isolation structures. The results show that the improved isolation bearing maintains a smaller horizontal stiffness before the displacement is limited, giving full play to the isolation performance. After that, the horizontal stiffness of the bearing is enhanced, which can effectively control the displacement of the seismic isolation layer. The lead-core can give full play to the energy dissipation characteristics. Under the four performance levels, the improved isolation structure has the highest safety reserve and the best collapse resistance. The use of improved isolation bearings can reduce the repair cost of the structure and casualties.

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