11

地盤物性の不確実性が地盤の地震応答特性に与える影響検討

モンテカルロシミュレーションによる地震応答解析

畑 明仁*1・志波 由紀夫*1

設計の基本的な考え方が仕様規定型から性能規定型に移行する中で,地震時の構造物の耐震性能を評価するためには,地震時の地盤および構造物の応答特性をより正確に,かつその不確実性も含めて評価することが必要となる。しかしながら一方で,地盤は本来的に不均一性を有し,限られた地盤調査データから地震時の地盤応答を一意に評価することには現実的に困難が伴う。そこで,地盤物性のばらつきが地盤の地震応答特性に与える影響を数値的に検討し,物性のばらつきと応答値のばらつきの関係を評価した。その結果,地震時の地盤振動モードが1次モード卓越型であるため,その応答の変動は地盤の1次固有周期により単純に整理できることを示した。また,モンテカルロシミュレーションの結果は,確定論的な感度解析結果周辺に分布するため,より計算負荷の少ない確定論的解析結果から確率論的解析結果を間接的に概略評価できることを示した。

キーワード:  地震応答,応答スペクトル,不確実性,空間的変動,モンテカルロシミュレーション

*1 技術センター 土木技術研究所 土木構工法研究室

Uncertainty Analysis of Earthquake Response of Subsurface Ground

Monte-Carlo Simulation of Dynamic Earthquake Response Analysis of Subsurface Ground

Akihito HATA*1 and Yukio SHIBA*1

From the point of view of aseismic design, it is very important to predict the dynamic response of the subsurface ground to earthquakes. Due to the shift from specification-based design to performance-based design, assessing the dynamic response of the ground and its reliability has become more important. However, accurately estimating the dynamic response of the ground from scarce in-situ data is never easy because of the inherent uncertainty regarding the soil's properties. In this study, a series of Monte Carlo simulations of dynamic earthquake response analyses were carried out in order to obtain a fundamental understanding of the effect of soil variability on the dynamic earthquake response of the ground. These analyses showed that the behavior of the various earthquake responses caused by soil variability can be estimated accurately and effectively by considering the relationship between the 1st eigen frequency of the ground and the maximum response, and that the behavior can be predicted with a few deterministic calculations. This basic feature is due to the fact that the dynamic earthquake response of the ground is dominated by the 1st mode of the vibration.

Keywords:  earthquake response, response spectrum, uncertainty, spatial variability, monte-carlo simulation

*1 Civil Structure and Material Research Section, Civil Engineering Research Institute, Technology Center