松软场地上桩筏基础AP1000核岛结构的三维非线性地震反应特性

松软场地上核岛结构的地震安全正成为一个挑战性的重大工程问题。选取代表性的近场强震、中远场强震和远场大震记录作为基岩地震动，考虑场地工程地质特性、土体非线性和人工边界条件，对松软场地-桩筏基础-AP1000核岛结构三维体系进行非线性地震反应分析，结果表明:核岛结构谱加速度的卓越周期与基岩地震动的基本相同，对与核岛主体结构基本频率相近的地震动分量的反应更为强烈，冷却系统水箱“晃动水”的地震反应对核岛结构的影响类似于鞭梢效应；核岛结构的峰值加速度放大系数随结构高度增大，近场和远场强震作用时，该放大效应主要取决于核岛结构自身特性及基岩地震动经土层到核岛底部的传播；核岛结构相对其底部的峰值相对位移随结构高度增大，且远场大震作用时的反应更为强烈；随基岩峰值加速度的增大，核岛结构的峰值加速度放大效应减弱、峰值相对位移反应增大。地基柔性及土-结构相互作用的耦合效应对输入地震动具有高频过滤、低频放大效应，从而使核岛结构下部的峰值加速度显著放大、中上部的峰值加速度显著减小。

3D NONLINEAR RESPONSE CHARACTERISTICS OF THE PILE-RAFT-SUPPORTED AP1000 NUCLEAR ISLAND BUILDING IN SOFT DEPOSITS SUBJECTED TO STRONG GROUND MOTIONS

The seismic safety of nuclear islands constructed in loose and soft deposits subjected to strong earthquake motions is becoming a major engineering challenge.An example of such nuclear islands is the AP1000 nuclear islands located in the coastal deposits,China.Using the three-dimensional(3D)finite element method,we conducted a nonlinear seismic response analysis of a pile-raft-supported AP1000 nuclear island building.In the proposed response analysis,the engineering geology characteristics and nonlinear dynamic behavior of the soils,the artificial boundary conditions and the simulation model were considered in detail.A special emphasis was given to the 3D model for the pile-raft-supported AP1000 nuclear island building and the input bedrock motions from the near-field,middle-far-field,and far-field strong earthquakes.The spectral accelerations(SAs)of the nuclear island building were more intense to the bedrock motion frequency components close to the fundamental frequency of the main structure of the nuclear island.The SA predominant periods were almost the same as those of the bedrock motions.The influence of the seismic responses of the sloshing water in the water storage tank(cooling system)on the nuclear island building was similar to the whipping effect.The peak acceleration amplification factors(PAAFs)increased with the increasing nuclear island heights.The PAAFs were mainly dependent on the nuclear island itself and the seismic wave propagating from bedrock to nuclear island base through soft deposits for the near-field and far-field strong earthquake motions,respectively.The peak relative displacements(PRDs)between the various nuclear island heights and its base increased with the increasing heights,and the PRDs to the far-field strong earthquake motion ware more intense.With the increasing peak bedrock accelerations,the PAAFs of the nuclear island building were decreased while the PRDs were increased.The flexible ground and the soil-pile-raft-nuclear island building interaction had an effect on the highfrequency de-amplification and the low-frequency amplification for the bedrock motions.It significantly increased the peak acceleration at the lower part and decreased it at the middle-upper part of nuclear island building.