考虑场地类别的阻尼比修正系数研究

Research on modification factors of damping ratios considering site conditions

阻尼比修正系数B用于调整临界阻尼比不同于0.05时的反应谱值,它对减震结构、隔振结构以及弹塑性体系的简化设计与分析具有重要意义。本文按照我国现行抗震规范规定的场地分类方法,分别应用四类场地共计136条地震记录,对阻尼比为0.05、0.1、0.2、0.3、0.4、0.5的弹性单自由度结构体系的相对位移反应谱、相对速度反应谱、绝对加速度反应谱进行计算分析,从定性到定量系统研究了地震作用下场地分类、阻尼比以及结构周期对相对位移反应谱阻尼比修正系数Bd、相对速度反应谱阻尼比修正系数Bv和绝对加速度反应谱阻尼比修正系数Ba的影响规律,结果表明:随着阻尼比的增大,场地分类对阻尼比修正系数的影响程度逐渐增大,其中场地条件对Ba的影响更加显著,然而数据分析表明,场地条件对阻尼比修正系数最小值的影响很小。在IV场地上,阻尼对长周期结构的减震效果明显优于其它三类场地。最后通过非线性回归分析,建立了与场地类别、结构周期以及阻尼比相关的阻尼比修正系数Ba、Bd、Bv的计算公式。这部分的结果可以应用于减震结构基于性能的抗震设计方法中。

Damping ratio modification factors （DMFs） are used to adjust the response spectral values corresponding to damping ratios other than 5 %. In the simplified analytic methods for structures with energy dissipating systems or equivalent linear elastic systems＇, DMFs are very useful. The detailed and systematic statistical studies on DMFs considering site conditions are carried out by using a total of 136 earthquake records. The factors are computed from the displacement, velocity and acceleration response spectra of single-degree-of-freedom systems with different damping ratios. Considered here is four types of site conditions characterized by site Classes I- IV in accordance with China Code for seismic design of buildings. The influence of period of vibration, level of damping ratio and soil condition on DMFs is evaluated and discussed. After comparing with the mean ratios, it is shown that DMFs are dependent on site conditions. Site effects simply increase as the level of damping ratios is raised. DMFs derived from the true acceleration response spectra Ba are more sensitive to site conditions than those derived from the displacement response spectra Bd and velocity response spectra Bv. The site condition has little effect on the minimum value of DMFs. By means of nonlinear regression analysis, the formula of DMFs are derived from the displacement, velocity and acceleration responses in which the site conditions, the vibration period and the viscous damping ratio are considered.