ブックタイトル竹中技術研究報告書No70

概要

竹中技術研究報告書No70

TAKENAKA TECHNICAL RESEARCH REPORT No.70 2014竹中技術研究報告No.70 2014Seismic Observation of Piled Raft Foundation Subjected toUnsymmetrical Earth Pressure常時偏土圧を受けるパイルド・ラフト基礎の地震観測＊1＊2Junji Hamada濱田純次Naoki Aso麻生直木＊3＊4Atsunari Hanai花井厚周Kiyoshi Yamashita山下清SummaryThe purpose of this study is to clarify the seismic performance of piled raft foundations based on seismic observationrecords. Seismic observation on piled raft foundation on medium stiff sand, supporting a seven-story building with threebasement floors, subjected to unsymmetrical earth pressure began just after the 2011 off the Pacific coast of TohokuEarthquake. The seismically monitored building is located in Tokyo, Japan. Accelerations of the building, dynamic sectionalforces of the piles and dynamic earth pressures on both sides of the embedded foundation and those beneath the raft wereobserved during 371 seismic events including an earthquake with a magnitude of Me7.1. The maximum acceleration of 0.322m/s 2 was observed on the building foundation. Based on the seismic records, it was confirmed that a lateral inertial force of thebuilding was supported by frictional resistance beneath the raft as well as shear forces of piles. It was also found that the ratioofthelateralloadcarriedbythepilestothelateralinertialforceofthebuildingwasestimatedtobeabout10to20%.Keywords: ?piled raft foundation, seismic observation, unsymmetrical earth pressure,the 2011 off the Pacific coast of Tohoku Earthquake梗概本研究の目的は，パイルド・ラフト基礎の地震時挙動を地震観測データより明らかにすることである。偏土圧を受ける基礎の地震観測は，2011年東北地方太平洋沖地震後に行った。観測した建物は砂地盤上に建つ7階建て，地下3階建ての建物である。偏土圧を受けるパイルド・ラフト基礎の地震観測を行い，マグニチュード7.1を含む371波の地震動に対して建物の加速度，杭の断面力および地下壁の側面土圧を計測した。基礎の最大加速度0.322m/s 2が観測された。建物に設置した地震計より建物慣性力を評価し，建物慣性力と杭頭せん断力を比較することで，基礎底面に流れた水平荷重を算定し，杭の水平荷重分担率は10～20%と評価された。キーワード：パイルド・ラフト基礎，地震観測，偏土圧，2011年東北地方太平洋沖地震1 INTRODUCTIONIt is important and necessary to develop more reliable seismic design methods for piled raft foundations, especially in highlyactive seismic areas such as Japan. In the last decade, shaking table tests and static lateral loading tests using centrifuge modelor large scale model (Watanabe et al. 1）, Horikoshi et al. 2）, Matsumoto et al. 3）, Katzenbach & Turek 4）, Matsumoto et al. 5）, Hamadaet al. 6）) and analytical studies (Kitiyodom & Matsumoto 7）, Hamada et al. 8）) have been carried out. Mendoza et al. 9）reported onthe static and seismic behaviour of a piled-box foundation supporting an urban bridge in Mexico City clay. The reportexamined the response of the soil-foundation system that was recorded during two seismic events in 1997 in which thefoundation’s maximum horizontal acceleration was 0.31 m/s 2 . Recently, Yamashita et al. 10）and Hamada et al. 11）had successfullyrecorded seismic response of piled raft foundation supporting a base-isolated building during the 2011 off the Pacific coast of＊1Chief Researcher, Research & Development Institute, Dr. Eng.技術研究所主任研究員博士（工学）＊2Group Leader, Tokyo Main Office, Building Design Department東京本店設計部グループ長＊3Manager, Tokyo Main Office, Building Design Department東京本店設計部課長＊4Executive Manager, Research & Development Institute, Dr. Eng.技術研究所専門役博士（工学）41