Frequency spectra characteristics of strong-motion acceleration recordings at liquefied sites
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摘要: 为研究液化场地上建筑物承受地震作用的特性，本文利用11组液化场地实测记录，对液化场地的地震动特征进行了分析。结果显示，场地液化后，地表加速度幅值减小，长周期成分显著增多，记录中出现明显的 “尖刺” 。对比国内外抗震规范设计反应谱与液化场地实测加速度反应谱，分析得出：在短周期T＜0.3 s，规范设计反应谱值与实测记录反应谱基本一致；在中长周期段0.3 s＜T＜1.5 s，规范反应谱值明显低于实测记录反应谱值；在长周期段T＞1.5 s，规范设计谱较实测记录反应谱值略低。基于5种数值方法模拟的液化场地地震动结果显示：周期T＜1.0 s时，数值计算的反应谱值基本高于液化场地实测反应谱值，或与之吻合；而周期T＞1.0 s时，数值计算的反应谱值均低于液化场地实测反应谱值。Abstract: To understand the characteristics of earthquake action on buildings at potentially lique-fiable sites, 11 acceleration records from the selected liquefied sites were analyzed to discuss the characteristics of ground motion. The results showed that the acceleration amplitudes were remarkably reduced after initial site liquefaction and that the long-period components increased significantly with apparent " spikes” recorded. Comparison of the design spectra widely used in seismic design codes, both domestically and internationally, with the acceleration spectra obtained in this study shows that: in the short period range T＜0.3 s, the design spectra were consistent with the recorded response spectra; in the medium and long period range 0.3 s＜T＜1.5 s, the design spectra were smaller significantly than the recorded response spectra; in the long period range T＞1.5 s, the design spectra was a little smaller than the recorded spectra. Five typical numerical methods are used to simulate liquefaction acceleration, the results demonstrated that the numerical methods could satisfactorily predict response spectral values for the period range T＜1.0 s, but generally lower than the spectral values for the long-period T＞1.0 s.
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Keywords:
- liquefied site /
- ground-motion records /
- seismic design codes /
- response spectra
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图 1 1995年神户地震中港岛液化场地水平向30° （a）和60° （b）的加速度记录
Figure 1. Acceleration time histories with horizontal angle both 30° （a） and 60° （b） recorded at Port Island in the 1995 Kobe earthquake
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图 2 1987迷信山地震中WLA的两条加速度时程记录
Figure 2. Two acceleration time histories recorded at WLA in the 1987 Superstition Hills earthquake
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图 4 液化场地地震动加速度反应谱Sa （a）和位移反应谱Sd （b）
Figure 4. Response spectra of ground motion acceleration （a） and displacement （b） at the collected liquefied sites
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图 5 新西兰抗震设计规范NZS 1170.5 与2011年基督城地震的实测液化场加速度反应谱对比
Figure 5. Comparison of seismic design spectra NZS 1170.5 with the acceleration response spectra at liquefied sites in 2011 Christchurch earthquake
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图 6 不同规范的基本地震设计谱与液化场地加速度反应谱对比
Figure 6. Comparison of seismic design spectra by different seismic design codes with the acceleration response spectra at the liquefied sites
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图 7 WLA试验场井下7.5 m处记录的两条迷信山地震的加速度时程
Figure 7. Two acceleration time histories of the Superstition earthquake recorded at the WLA site 7.5 m underground
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图 8 迷信山地震中WLA试验场记录的两条实测加速度时程与不同数值方法得到的地表加速度时程对比
Figure 8. Comparison of acceleration time histories of the Superstition earthquake calculated by different numerical methods with two acceleration time histories recorded at WLA
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图 9 实测记录加速度反应谱与不同数值方法计算的地表加速度反应谱对比
Figure 9. Comparison of ground acceleration response spectra by different numerical methods with the res-ponse spectrum calculated by recorded accelerations
表 1 WLA场地土层参数 （Youd，Carter，2005）
Table 1 Soil parameters of WLA site （Youd ，Carter，2005）
土层
编号土类 厚度/m 干密度
/（kN·m−3）vS/（m·s−1） 1 粉土至含黏粉土 3 15.7 120 2 粉砂至砂质粉土 4 17.3 140 3 粉质黏土 8 20.4 190 
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