軸力を考慮した4本鋼管群杭の保有水平耐力に関する実験的研究

Abstract

鋼管杭は円筒形の鋼材であるために, 変形追従性のよい特性を持ちながら, 局部座屈という小さな変形時で終局限界となる弱点を有し, 限界状態設計法では不利になると言われてきた。そこで, 杭頭部にコンクリートを充填して座屈を防止し, せん断耐力を高めて終局限界状態を鋼材の破断強度の付近まで持続せしめる, 複合構造が用いられる.本研究では, 中詰めされた4本鋼管群杭の保有水平耐力を検討するために, まず気中において軸力を考慮した水平載荷試験を実施した。さらに, 砂地盤中の鋼管群杭基礎の遠心載荷実験を実施し, 杭頭部の充填コンクリートの効果(水平耐力の増大変形性能と初期剛生の向上)を確認した。

In order to investigate the resistance of axially‐loaded steel piles subjected to the cydic lateral load, a modelconsisting of 4 steel pipe columns was tested.From the model tests the mechanisms for the decrease in lateral bearing capacity of steel pipe column were known.As the column is laterally loaded, the compression stress at the top and bottom part of the column increases. Once the compression stress reaches the limiting value, the top and bottom of column will cripple due to the large compression force. Consequently, the lateral bearing capacity will decrease. This lateral bearing capacity can be increased, if the concrete is castd inside the pipe.To make a more realistic model, an experiment on 4 steel pipe piles embedded in sand was investigated.Under the centrifugal force field, the cyclic load is applied to the axially‐loaded model piles. From this model test the ultimate strength and the behavior of axially‐loaded steel pipe piles to the cydic lateral load can be examined.In addition, this experiment helped to verify the effect of concrete cast inside a pile.