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 2014Fig. 4 Time-dependent earth pressure acting on side wallsThe axial load of the pile and the earth pressures acting on side wall flactuate according to a season. The seasonal variationof the incremental earth pressures of D8-2, D9 shows opposite relation, that is positive and negative.5 SEISMIC RESPONSE OF PILED RAFT FOUNDATIONAccelerations of the building, dynamic sectional forces of the piles and dynamic earth pressure on both sides of theembedded foundation as well as that beneath the raft were observed during 371 seismic events from March 23 in 2011 to April30 in 2014, including an earthquake with a magnitude of Me7.1. The maximum acceleration of 0.322 m/s 2 was observed on thebuilding foundation. Figure 5 shows observed maximum accelerations of these seismic events and Fig. 6 shows the number ofthe events every month. It can be seen that the number of the events decreased gradually after April, 2011.Fig. 5 Maximum accelerations of seismic events Fig. 6 Number of seismic event per month5.1 Observed Seismic Response of FoundationFigure 7 shows the time histories of the measured accelerations during the seismic event on April 16, 2011 with a magnitudeof 5.9 and epicenter of south Ibaraki, in which the maximum acceleration of 0.322 m/s 2 was recorded in X-direction.Figure 8 shows the time histories of accelerations, sectional forces of the piles and earth pressures amplified between 20 and30 s including the main shock. The dashed lines indicate the time when the inertial force of building was maximum andminimum, i.e., time of 22.96 sec (Time B) and time of 23.84 sec (Time A), respectively.The sectional forces were estimated from the strains measured at the steel reinforcing bars in the piles. The bending momentswere calculated using the measured strains from a couple of strain gauges and the shear forces were calculated from dividingthe difference between the two sectional bending moments by the distance of the two sections. Young’modulus of concretewas assumed to be 2.1 E +7 kN/m 2 .45