改良版個別要素法を用いた無筋コンクリート橋脚の振動台実験の再現解析

Abstract

地震による無筋コンクリート橋脚の典型的な被害形態は, 打継目における水平ずれと打継目下側のコンクリート端部の破壊である. 地震時安全性の評価には, 数値解析によるアプローチが有用であるが, 無筋コンクリート橋脚に適した解析手法は確立されていない. 本研究では, 離散体の解析手法である改良版個別要素法に着目した. まず, 摩擦特性に関して従来の改良版個別要素法が有する要素数依存性の問題を解決する方法を提案した. 次に, 振動台実験の再現解析を行った. その結果, 供試体がほとんど破壊しないケースでは, 水平ずれを良好に再現でき, 非破壊または軽微な破壊を生じる結果となった. 供試体に顕著な破壊が生じたケースでは, 水平ずれの向きと滑動方向の打継目下側端部が破壊することを再現できた. 回転角は過小評価となり再現性に課題を残した.

The typical damage pattern of plain concrete piers during earthquakes is horizontal gap at the cold joint of a pier and falling down of concrete pieces from the pier under the cold joint. It is necessary to develop a numerical analysis method suitable for plain concrete piers to evaluate their seismic safety against the future earthquakes. With this background, this study investigated the applicability of the refined DEM for the dynamic analysis of plain concrete piers. First, it was found that the original refined DEM has a problem of overestimating friction properties. Therefore, the method was proposed to accurately simulate the friction properties by just modifying the arrangement of springs. Next, a shaking table test of a plain concrete pier was simulated, and the analytical and experimental results were compared. In the analysis, five acceleration histories with different peak acceleration values were input. In the case of smaller accelerations where the specimen suffered slight failure, it was found that the horizontal dislocation and failure occurrence situation was simulated with good accuracy. On the contrary, in the case of larger accelerations where the specimen suffered severe damage, it was found that the failure occurrence situation was barely simulated. It was also found that the refined DEM underestimates the rotational angle for all cases.