A Shaking Table Test of Scaled Model for an Emergency Diesel Generator System for Evaluation of Seismic Force Decrease by Using a Spring-Viscous Damper System

Abstract eng:
The effectiveness of a coil spring-viscous damper system for a seismic isolation of an Emergency Diesel Generator (EDG) in Nuclear Power Plants (NPP) was evaluated through a shaking table test and a numerical analysis. The EDG system consists of an engine, a generator and a concrete foundation. Net weights of the engine unit, the generator unit, and the concrete mass are 912 kN, 392 kN, and 2,474 kN, respectively, and the total weight is 3,779 kN. It is impossible to perform a real scale shaking table test for an EDG system. Therefore, a scaled EDG model was constructed using steel and concrete blocks. Total weight of the test model was 39 kN and the steel blocks were placed to have an equivalent mass center for the prototype. For the seismic isolation of the EDG test model, a spring-damper unit that consists of a combination of 2 coil springs and one viscous damper was adapted. The stiffnesses and the damping coefficients of the spring-damper unit for the vertical and horizontal directions were determined by a mechanical characteristic test. The test model was supported by 4 spring-damper units. A shaking table test for an EDG model was conducted for an evaluation of the seismic isolation performance of a coil spring-viscous damper system. An artificial time-history corresponding to the scenario earthquake for a Korean nuclear site and US NRC design spectrum were used as an input motion, and three peak acceleration levels were applied. The effectiveness of the coil spring-viscous damper system was evaluated by the ratio of the maximum acceleration responses measured at the model to the table acceleration. A numerical model for the test model was constructed and also a numerical analysis was performed by using the same seismic input motion. The EDG model tests and numerical analysis showed that the spring-viscous damper system could reduce the seismic force transmitted to the EDG by up to 50 percent.

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