基于反应谱衰减关系和理想化反应谱模型的我国规范谱长周期段研究

Research on long-period segments of Chinese code response spectrum based on the ground motion attenuation relationship of response spectrum and the idealized response spectrum models

相对于我国各行业抗震规范反应谱下降段呈现的多样性,欧美规范谱基于理想化反应谱模型,其长周期下降段的规定形式统一,且由第二特征周期TD确定。基于理想化反应谱模型,TD的确定与位移谱形态、“结构所需周期范围”等概念相关。基于我国区划图研究中大量采用NGA数据库的地震动记录及以地震动峰值加速度分区值表达地震强度的现状,以理想化反应谱模型为我国规范谱模型,以NGA数据库BSSA 14公式为工具,对TD建议值等进行研究。首先通过理想化反应谱模型与TD计算公式的阐述,明确欧美规范谱长周期下降段的衰减指数1、2是由理想化反应谱模型定义决定的确定性参数,此时长周期下降段函数由TD唯一确定;其次,在NGA数据库提供的地震动衰减关系中,比选出与我国规范考虑因素吻合性最好的BSSA 14公式,并以其作为基于地震动记录统计的反应谱公式,分析位移谱曲线形态类型及由于位移谱谱值截取周期Tcut不同而引起的位移谱曲线形态类型随震级、距离、场地类别的分布变化;最后,基于BSSA 14,考虑“结构所需周期范围”,给出以我国规范地震动峰值加速度分区值为参照的TD建议值。此研究可为我国抗震规范谱长周期下降段的研究提供参照。

The long-period descending segments of response spectrum in different industry codes in China are quite different.In response spectrum of European and American codes,which are all based on the idealized response spectrum model,they have the same form,and are determined by the value of TD,the second corner period.In ide⁃alized response spectrum model,calculating the value of TD is related to the factors,such as the curve shape of dis⁃placement response spectrum,‘the necessary range of structural natural period’and the others.Considering the present situations that a large number of ground motion records from NGA database is adopted in the research of“Seismic Ground Motion Parameters Zonation Map of China”in which earthquake intensity are scaled by the partition value of the seismic peak ground acceleration,the values of TD are investigated by taking the idealized response spectrum model as code response spectrum model and using the formula BSSA 14 from NGA database.In this paper,firstly,by relating the conceptions of the idealized response spectrum model and the formulas of TD,it is illustrated that the attenuation power index 1 and 2 of the long-period descending segments of response spectrum of the European and American code are two fixed values and are determined directly by the definition of the idealized response spectrum model itself,and the long-period descending segments are determined only by the parameter,TD.Then,from the ground motion attenuation relationships provided by NGA database,BSSA14 formula which has the most agreement with the consideration conditions in China′s code is selected,and using BSSA14 as the statistical response spectrum formula based on ground motion records,curve shape types of displacement response spectrum,and its variation of distribution varying with magnitude,distance and site classification,caused by truncation period Tcut,are analyzed.Finally,based on BSSA 14,considering‘the necessary range of structural natural period’,the TD value varying with the partition value of seismic peak ground acceleration in China′s code is established.This study can provide a reference for the research of long period decline segments of the code response spectrum in China.