弹塑性地震反应谱的长周期特性研究

Study on characters of long period portion of inelastic spectra

在基于性能抗震设计中弹塑性反应谱在计算结构地震位移反应方面越来越受到重视。利用统计分析方法研究了等强度的延性需求谱和等延性的强度折减系数谱的长周期(至5 s)区段的特性,关注的重点是等位移准则和场地条件影响。给出了若干具有工程价值的结论:一是周期介于1.5Tg(地震动特征周期)和2.5 s之间的结构可近似认为等位移准则成立且与场地条件关系不大,这样确定的强度折减系数当位移延性系数小于等于4时结果将是偏于安全的;二是结构周期大于2.5 s后以硬土场地等延性强度折减系数谱或等强度延性需求谱代替软土场地谱求解系统强度需求或延性需求,将会得到偏于安全的结果。

More attention has been paid to inelastic design spectra with the development of performance based seismic design, because it can be used to estimate the maximum displacement demand of structures. Characters of long period portion of inelastic spectra are studied by the statistical analysis. The equal displacement rule and effects of soil conditions are considered. It is shown that ： （ 1 ） the equal displacement rule is true and the structure is independent of soil conditions when the period of the structure is between 1.5 Ts （ characteristic period of ground motions） and 2.5s. The strength reduction factor computed by this rule can be used conservatively when the displacement ductility factor is smaller then 4; （2） the constant ductility inelastic spectrum of strength reduction factors or ductility demand spectrum with constant strength reduction factors on hard site can be used to overestimate the seismic displacement demands or the seismic strength demands on soft site when the period of the structure is larger than 2.5s.