基础提离对核电站结构地震响应的影响分析

Analysis on the influence of foundation uplift on structure seismic response

当地震足够大时结构基础将会与下卧地基土发生分离,即所谓的基础提离现象。但该现象在常规的土-结构相互用(SSI)的地震响应分析中常常被忽视。核电站结构(NPP)由于特殊性,其设计地震强度一般较大,因而有可能发生基础提离现象。基于某简化核电站结构,利用大型通用软件ANSYS的接触面功能和弹簧单元,分别进行了四种工况的计算:1基础固定;2考虑基础提离,不考虑土-结构动力相互作用效应;3不考虑基础提离,但考虑土-结构动力相互作用效应;4同时考虑基础分离和土-结构动力相互作用效应。通过对比分析,确定合适的土-结构动力相互作用计算方法以及基础提离对核电站结构地震响应的影响。计算分析表明:1土-结构相互作用对核电站结构地震响应的影响不容忽视;2基础提离主要影响核电站结构竖向地震响应,而对结构水平向地震响应的影响较小。本文研究成果可为核电站结构的抗震分析提供参考。

The structure foundation may be separated from the supporting soil if the earthquake is strong enough, which is the so called phenomenon of foundation uplift. This phenomenon, unfortunately, is always neglected in seismic response analysis of soil-structure interaction （SSI） system. The designed seismic level for nuclear power plant （NPP） is usually very high because of its specificity, therefore, the foundation of nuclear power plant will probably be separated from the supporting soil. Based on a simplified NPP calculation model and by employing the contact function and spring element in the software ANSYS, four cases were considered ： ① foundation is fixed ; ②foundation uplift is considered and SSI effect is not considered; ③ SSI effect is considered and foundation uplift is not considered; ④ both foundation uplift and SSI effect are considered. The influences of SSI and foundation uplift on structural seismic response were analyzed by comparing the computation results. It is shown from the computation results that the influence of SSI on structural seismic response can not be neglected; foundation uplift influences structural vertical response mainly, and has a very little influence on structural horizontal response. The results provide some references to seismic design of NPP.