【摘要】 针对基岩明显起伏、土层非均匀分布的典型河口盆地场地,考虑土体非线性特征,采用黏弹性人工边界模拟无限域对地震波动的影响,建立大尺度精细化二维有限元模型,分析了盆地地表地震动幅值、频谱、持时、传递函数特征,探讨了基岩起伏土层的地震动聚集效应及盆地边缘效应。结果表明:(1)盆地近地表土层表现出不同程度的地震动放大效应,且随土层深度增加呈非单调递减特征,基岩突变处地震动聚集效应明显,盆地两侧产生较为显著的边缘效应;场地中、长周期地震动的放大作用显著;(2)多遇地震、偶遇地震和罕遇地震水平时,场地卓越周期依次介于0.35~0.65 s、0.40~0.75 s和0.50~1.05 s之间;给出了盆地地表PGA(地表峰值加速度)、卓越周期均值等值线图及地表加速度反应谱放大因子建议值,地表设计地震动参数amax(地震影响系数)与Tg(特征周期)明显大于现行《建筑抗震设计规范》取值;(3)盆地特殊位置地表地震动持时得到不同幅度增长,且与输入地震动特性相关;(4)该盆地对0.5~2.0 Hz频段基岩地震动的放大效应比较显著,对小于0.2 Hz或大于2.5 Hz的基岩地震动,该盆地地震动放大效应不明显;(5)福州城区及其邻近区域地震动放大效应普遍较大。大尺度二维非线性分析一定程度上能合理反映微地形起伏、土层分布及土体非线性对地震波传播过程的影响。更多还原

【Abstract】 Based on the explicit FE method and parallel computing cluster platform of ABAQUS,a large-scale refined two-dimensional(2D) nonlinear FE model is developed in the time domain with considering the heterogeneity of ground soils,for a typical site on the estuarine basin with undulating bedrock and nonuniformly distributed soil layers.The artificial viscoelastic boundary condition is proposed for simulating the semi-infinite field,the main characteristics of basin surface ground motion are analyzed,including the motion amplitude,spectrum,duration and transfer functions,and the accumulation effect of ground motion and edge effect of basin are investigated.The results show that:(1) The amplification effect at different observation points on the basin ground surface is observed;and the peak ground acceleration(PGA)of basin ground surface displays a non-monotonic decrease with soil depth;the prominent accumulation effect is found to be at particular positions where the bedrock surface sharply undulates,and the pronounced edge effect is found to be on both sides of basin;the moderate and long-period ground motions of the basin are significantly amplified compared to the short-period motions.(2) For the earthquakes with high,moderate and low occurrence probabilities,the predominant periods of the basin are 0.35-0.65 s,0.40-0.75 s and 0.50-1.05 s,respectively;the mean value contours of the peak ground acceleration and site predominant periods of the basin are plotted,and the recommended values of the amplification factor of ground motion acceleration response spectra for different period intervals are given.The seismic effect coefficient amax and characteristic period Tg of the design parameters of ground motion by this paper are significantly larger than those of the Chinese code for seismic design of buildings.(3) Ground motion durations at different points of basin ground surface extend over several orders,and the duration is also closely related to the bedrock motion characteristics.(4) Amplification effect and accumulating effect of the basin ground motion are more significant for the frequency band from 0.5 Hz to 2 Hz;while for thefrequency band lower than 0.2 Hz or higher than 2.5 Hz,the ground motion amplification characteristics are insignificant.(5) Ground motion amplification effects in Fuzhou city downtown area and its adjacent areas of the basin are generally larger,compared to other areas.It is indicated that the large-scale two-dimensional nonlinear FE model can describe the influence of micro topographic relief and nonuniformly distributed basin soil layers on seismic wave propagation.更多还原