基于计算地震动特征一致性的场地分类方法探讨

    Discussion on site classification method based on consistency of characteristics of calculated seismic motion

    • 摘要: 基于1137个钻孔资料的场地模型及相应的土层地震反应分析计算结果,从场地地震动峰值加速度和特征周期两方面讨论分析了中国《建筑抗震设计规范:GB50011—2016》和美国规范IBC(International Building Code)中的场地分类方法。依据场地效应一致性分析得出:在中硬土场地上,美国的C类场地的离散性最小;在中软土场地上,中国的Ⅲ类场地表现出一定的弱势性;在软弱土场地上,中国的Ⅳ类场地优势性明显。总体上中国的双指标分类方法体现了一定的优势性。因此,提出了新的场地分类方法,方法中按照覆盖层厚度和30 m两者较小值的土层计算等效剪切波速,并将目前的Ⅱ类场地划分为Ⅱ1和Ⅱ2,将Ⅲ类场地中覆盖层厚度大于50 m且等效剪切波速小于等于170 m/s的场地归类到Ⅳ类场地,500 m/s以下的等效剪切波速分界线提高20 m/s。研究为建立更合理的场地分类方法提供新的解决方案。

       

      Abstract: Based on site models derived from 1137 drilling data and corresponding computing results of seismic response analysis of soil layers, this paper analyzes and discusses site classification methods in the Chinese Code for Seismic Design of Buildings (GB50011-2016) and the American Code IBC (International Building Code) from the perspectives of peak acceleration and characteristic period of the site ground motions. According to the consistency analysis of site seismic effects, it can be concluded that: in medium-to-hard soil sites, the dispersion of Class C sites in the United States is the smallest; in soft-to-medium soil sites, Class Ⅲ sites in China exhibit certain weaknesses; in soft soil sites, China's Class Ⅳ sites have more obvious advantages. Overall, China's double index classification method demonstrates certain advantages. Therefore, a new site classification method is proposed, in which equivalent shear wave velocity is calculated based on the soil layers in the depth range of smaller values between the covering layer thickness and 30 m. In current Class Ⅱ sites are divided into class Ⅱ1 and Ⅱ2 sites, and Class Ⅲ sites with a soil layer thickness greater than 50m and equivalent shear wave velocity less than or equal to 170 m/s are classified as Class Ⅳ sites, the boundary limits of equivalent shear wave velocity below 500m/s are increased by 20 m/s. The study provides a new solution to establish a more reasonable site classification method.

       

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