Research and Development of Three-Dimensional Isolation System for Sodium-Cooled Fast Reactor: Part 4 — Proposal of Optimal Combination Method for Disc Spring Units and Newly Friction Model for Sliding Elements

The authors proposed a newly three-dimensional isolation system, consisting of a rubber bearing, vertical oil dampers and disc spring units, to reduce the seismic response in the vertical direction as well as horizontal direction. This isolation system is employed with a number of disc spring units to provide the vertical restoring force to the superstructure. The disc spring units are combined by three disc springs in parallels and they are are stacked in six serials. The vertical restoring force has susceptible to the variation forces for the individual disc springs because the disc spring units are combined in the six serials. The The purpose of this paper is to present two kinds of proposal to improve the quality control of our isolation system and the prediction accuracy of seismic response. The first is to create the the optimal combination method for the disc spring units using the meta-heuristic algorithm to minimize the variation of vertical vertical restoring force. The proposed optimal method was verified through the result of static loading tests using the 72 disc springs which have the half dimensions to full scale. The second is to create a newly analytical model for the friction force caused by polymeric materials. The proposed analytical model was verified by comparing the loading test results. Moreover, the seismic isolation performances were clarified by the seismic response analysis that consider the vertical restoring force of the disc spring units which were combined using the optimal method and the friction force of sliding elements which were modeled by the proposed friction model. This analytical result revealed that our isolation system can reduce the seismic response not only for the high frequency components but also the low frequency ones.