In order to evaluate bearing capacity and pull-out resistance of piles under alternately cyclic vertical loading, monotonic and cyclic loading tests were conducted on a pile with or without a wing plate under a centrifugal acceleration of 30 G. In the pulling-out process, cyclic loading decreases the shaft friction and the force acting on a wing plate. The decrease is more significant in the shaft friction than in the wing force. In contrast, in the pushing process, cyclic loading decreases the shaft friction but increases the wing force and the end resistance.%高層建築，塔状建築などでは地震荷重や風荷重を受けた際，転倒モーメントによって生じる鉛直荷重を杭が繰返し受けることで，杭の周面摩擦が低減し，特に引抜き側で危険になる可能性がある．また，2011年東北地方太平洋沖地震後の調査では，津波の被害が甚大であった地域で，一部の杭基礎が引抜けた状態で建物が転倒している例などが報告されている．
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