基于地震动预测残差分析的工程场地分类标准检验与评价

EVALUATING THE SCHEMES OF ENGINEERING SITE CLASSIFICATION BASED ON RESIDUAL ANALYSIS OF GROUND MOTION PREDICTION

各国抗震设计规范采用不同的指标定义场地分类标准,以中、日、美三国的标准最具有代表性,其能否合理体现相同类别内场地放大的集中性、不同类别间场地放大的差异性鲜见有研究开展检验与评价。针对此问题,利用日本KiK-net台网的强震动记录和台站的钻孔资料,分别以三国分类标准划分台站场地类别,基于地震动预测残差分析方法计算台站的真实场地放大因子,比较分析不同分类标准、不同场地类别的场地放大因子均值及标准差分布情况。得到如下结论:在PGA和SA的短周期段(T<0.1 s),以场地自振周期TS作为分类指标的日本规范没有体现出不同类别间场地放大效应的差异性,以地表20 m内等效剪切波速VSE及覆盖层厚度双指标的中国规范和以地表30 m以内平均剪切波速VS30为指标的美国规范均能较好地反映不同类别间场地放大效应的差异性;日本规范在整体上体现相同场地类别内场地放大的集中性方面表现最好,对于长周期(T>2 s)地震动,中国规范则表现最优越;中国III类场地对中长周期地震动的放大体现出较大离散性,分类标准合理性还需要进一步深入分析。研究结果可为改进场地分类方法提供理论参考。

Different parameters are used for stipulating site classes in seismic design codes of different countries of the world,among which the schemes from China,Japan and U.S.A are the most representative.Few studies have been examined and evaluated whether the site classification scheme can functionally reflect the intra-class uniformity and inter-class separateness of ground motion site response.To examine the performance of site classification schemes,the strong motion records and borehole data from KiK-net seismograph networks are used,the sites of strong motion station are classified respectively according to the schemes from the three countries,and the site amplification factors are calculated based on the method of residual analysis of ground motion model.The mean and standard deviation of site amplification factors for each site class are compared among different classification schemes.The results show that:For PGA and short period(T<0.1 s)ground motion,the scheme from seismic code of Japan which uses site nature period(TS),does not reflect clearly the inter-class separateness;while the schemes of China and U.S.A.have better performance,because soil covering depth and equivalent shear wave velocity(VSE)are used in China and VS30 is used in U.S.A.In general,the scheme from seismic code of Japan is the best one in reflecting intra-class uniformity;but for long period(T>2 s)ground motion,the one from China performs best.Great variability of site amplification of medium-long period ground motions is observed for site class III defined by seismic code of China,calling for a further investigation on the rationality of its site classification scheme.The results achieved can provide theoretical support for improving site classification scheme in future.