地面运动双向最大加速度反应谱特性研究

在整理当前国内外双向水平地面运动反应谱值代表值后，本文认为考虑了记录仪器所有可能水平放置方向的加速度时程对应的所有单向加速度反应谱值中的最大值是双向水平地面运动反应谱值的最佳代表值，称其为双向最大加速度反应谱值（简称BdM谱值）。建立Ⅱ类场地地面运动数据库，考察Ⅱ类场地不同地面运动类型BdM谱和单向加速度反应谱Und谱的特性差异，结果表明：Ⅱ类场地同一地面运动类型下，二者在谱形上相似，但前者的动力放大系数普遍大于后者，且二者差距随着周期的增大而增大；同一周期谱值的平均值和标准差，前者分别为后者的1.2~1.4倍和1.1~1.4倍。另外，与BdM谱相比，我国规范Ⅱ类场地设计反应谱谱值在第一衰减段普遍偏小，在第二衰减段则低于很多地面运动类型的BdM谱值。因此，以我国设计反应谱作为设计地震力取值依据所设计出的Ⅱ类场地工程结构，其设计地震力取值水准高低不一，从而导致抗震安全性高低不一；以我国设计反应谱为目标谱选择地面运动记录预测出的Ⅱ类场地工程结构的地震反应，危险性水准不一，在统一的性能评价标准控制下，导致其实际抗震性能存在差异。

Study of maximum acceleration response spectrum for bi-directional ground motions

In this study, the domestic and overseas representative response spectra of bi-directional horizontal ground motions are reviewed. It is found that the maximum value of the unidirectional acceleration spectra corresponding to all the possible horizontal acceleration recorders is the best representative value for bi-directional horizontal ground motions, which is termed as the bi-directional maximum acceleration (BdM) spectrum. Ground motion database for the site of type II with various ground motions is created to consider the difference between BdM spectrum and unidirectional acceleration (Und) spectrum. The results show that: (1) firstly, for the same ground motion in site of type II, BdM and Und are similar in the shape of spectrum, but the dynamic amplification factor of the former is generally higher than that of the latter, and their difference may increase with the period of structure. The mean value and standard deviation of BdM spectrum are 1.2 to 1.4 and 1.1 to 1.4 times those values obtained from Und spectrum, respectively, at the same period. (2) Secondly, compared to BdM spectrum, the first descending part of the design spectrum for site of type II in the national code of China is generally smaller, while for various ground motion types, the second descending part is generally smaller than BdM spectrum. As a result, for the structures designed for site of type II based on the design spectrum in the national code of China, value levels of the seismic design force may not be consistent, leading to inconsistent seismic safety levels of structures. Particularly, when choosing ground motion records on the basis of the target design spectrum to predict the seismic responses of structures in site of type II, the risk levels shall be inconsistent, which may result in the difference in actual seismic performance when the structural design is controlled by the uniform evaluation criteria.