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液状化地盤において杭頭半剛接合構法を採用した建物の地震時挙動に関する解析的検討

石﨑 定幸^＊１・長尾 俊昌^＊１・時松 孝次^＊２

当社は，杭頭部の接合法として開発した杭頭半剛接合構法を比較的良質な地盤における杭基礎に適用し，耐震性の向上とコスト削減を実現している。本論文では，液状化地盤において杭頭半剛接合構法を採用した建物の地震時挙動の解析法として，半剛接合部の回転挙動を再現できる２次元有効応力解析手法を提案し，遠心模型実験のシミュレーションから，基礎根入れ部に外力として生じる地震時土圧が小さくなる効果や，優れた杭応力低減効果を再現できることを示した。また，液状化地盤において大きな変動軸力が生じる12階建ての実大建物を想定した解析から，半剛接合構法を採用することにより杭頭部の損傷を大きく低減でき，さらに，地中部に生じる最大曲げモーメントは剛接合とした場合と同等かむしろ若干小さくなる可能性を示した。

＊１ 技術センター 建築技術研究所 建築構工法研究室
＊２ 東京工業大学

An Analytical Study on Seismic Behaviour of a Building with Semi-Rigid Pile Head Connection Method in Liquefiable Ground

Sadayuki ISHIZAKI^*1, Toshiaki NAGAO^*1 and Kohji TOKIMATSU^*2

We have been developing a semi-rigid pile head connection method as a standard pile head design, which can economically improve earthquake resistance, and adopted the method for many buildings. In this paper, to evaluate a seismic behaviour of the building with the method in liquefiable ground, 2-D effective stress analysis considering rotational behaviours of the pile heads is developed. To verify the capability of the analysis for a reliable evaluation method, simulation analyses for dynamic centrifuge model tests of soil-pile-structure systems are conducted. It is confirmed that the analysis can evaluate the method’s two effects in liquefiable ground: the first is that seismic earth pressure acting on the footing as an external force decreases, and the second is that the maximum bending moment along the pile becomes smaller than that of rigid pile head connection. And to verify the seismic performance and safety of the building with the method in liquefiable ground, the analysis is applied to 12-floors reinforced concrete building in which high varying axial forces act on the pile heads. Through the analytical investigation, it is confirmed that the method can reduce the pile head damage considerably, and that the maximum bending moment with the method in the soil is rather smaller than that with rigid pile head connection method.