Evaluation of Nonstationary Frequency Properties of Earthquake Strong Ground Motions and Their Significance to Inelastic Responses of Structures

利用真实的强地面运动，我们评估了运动中包含的非平稳频率特性，并检查了非平稳运动可以产生过大的结构非弹性响应的证据。所得结果总结如下：1。本文收集了1989年Loma Prieta地震和1993年kushiroo -oki地震的强地震动记录，通过演化谱分析对强地震动的非平稳频率特性进行了评价。通过对Loma Prieta地震期间获得的运动数据的分析，我们将其非平稳性质分为过渡型、来临型、多主导型、三角洲型和平稳型五种类型。在讨论非平稳性与记录台站地基剖面的关系时，发现软地基台站得到的运动在频率内容上有较强的非平稳性的趋势。我们可以指出，地基条件与观测到的非平稳性质模式之间存在相关性。我们对结构在具有非平稳频率特性的运动下的非弹性响应进行了分析，并考察了非平稳特性对结构响应的意义。为了表示结构，我们建立了一个单自由度振荡系统，该系统具有所谓的双线性、克拉夫、退化三线性和面向原点的滞后规则，这些规则与结构的基本周期和强度的变化有关。我们提出了从产生的最大响应到弯矩所确定的等效周期来表示结构的非弹性响应。我们发现等效周期被拉长，使其等于激励运动的主导周期，这可能是具有非定常频率特性的运动在满足一定条件时产生过大响应的机制。少

Using real strong ground motions we evaluate nonstationary frequency properties included in the motions, and examine the evidence that nonstationary motions can generate excessively large inelastic responses of structures. The results obtained are summarized as follows;1. We collect the strong ground motion records obtained during those such as the 1989 Loma Prieta and 1993 Kushiro-oki earthquakes, and through evolutionary spectral analysis we evaluate nonstationary frequency properties of strong ground motions.2. Through analysis upon the motions obtained during the Loma Prieta earthquake, we group the nonstationary properties into five patterns that are named herein the transition, advent, multi-dominant, delta-shaped and stationary types.3. We find the tendency that motions obtained at stations with soft subsoil condition reveal strong nonstationary property in frequency contents when we discuss the nonstationary properties in correlation with the subsoil profile of the recording st … More ations. We can point out that correlation exists between the subsoil condition and the observed pattern of nonstationary properties.4. We perform inelastic response analysis of structures subjected to motions having nonstationary frequency properties, and examine significance of the nonstationary properties to responses of structures. To represent a structure, we establish a single-degree-of-freedom oscillating system that has the so-called bi-linear, Clough, degrading tri-linear and origin-oriented hysteresis rules associated with a variation of the fundamental period and strength of structures. We propose the equivalent period that is determined from the maximum response generated up to the moment to represent inelastic response of structure. We find the fact that the equivalent periods are elongated so as they equal the dominant periods of the exciting motion, which is the possible mechanism that the motions having nonstationary frequency properties can generate excessively large responses when certain conditions fulfilled. Less