SSI体系阻尼比实测及其分布规律研究

RESEARCH ON MEASUREMENT OF DAMPING RATIOS OF FULL-SCALE SSI SYSTEM AND ITS DISTRIBUTION LAW

阻尼比是结构动力分析的重要动力特性参数,目前规范采用的阻尼比是基于刚性地基或近似刚性地基的试验结果,未能考虑土与结构相互作用(SSI)效应。针对SSI效应问题,体系阻尼比的准确评估是其动力分析的重要前提。为了实现实际SSI体系阻尼比值较准确的识别,提出环境激励下SSI体系阻尼比测试与识别方法,并应用这一识别方法,给出西安及其周围地区82幢各类SSI体系基本等效黏滞阻尼比的实测识别结果。同时在实测阻尼比数据的基础上,初步研究实际SSI体系阻尼比的总体分布规律、影响因素和取值范围。

Damping level of a system is vital in dynamic response analysis. In civil engineering, damping ratio is commonly employed in characterizing the damping level of structure and is of great importance in aseismic design But so far, for most conventional building aseismic designs, the influence of the soil-foundation interaction on the structures is disregarded. The damping ratio adopted in current aseismic design is based on the experiments carried out on rigid soil-foundation. Since the soil-structure interaction（SSI） effect is universal, for the dynamic responses analysis of an in-situ building, it is in accordance with the actual case to involve SSI effect. For aseismic design of structures involving SSI effect, accurate experimental evaluation of damping ratios of SSI system is a necessary prerequisite. To accurately get damping ratio of the system, many identification methods have been proposed and developed. But so far, most of them cannot achieve success in identifying accurate in-situ damping ratios of buildings, i.e. SSI systems mainly because of the fact that the responses are significantly influenced by noise. In order to accurately evaluate the damping ratio of building involving SSI effect, a combined identification method using ambient excitation technique is proposed and simply introduced. Based on this method, the damping ratios of 82 in-situ buildings located in Xi＇an and their vicinal regions, which include all kind of upper structures in various materials, are investigated. The numerical range of damping ratios of the actual buildings involving SSI effect is shown as well as their distribution pattern. By means of a fitting curve, the variation tendency of damping ratios of in-situ buildings is revealed. And then, the influence factor of the damping ratios of actual buildings is preliminarily analyzed.