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. 7 Time histories of accelerations (April 16, 2011)Maximun bending moments at the pile head were about 50 kNm for both piles B and C. However the shear force of pile Bwas larger than that of pile C. Here, the bending moment of pile B at the pile head (-1.7 m) was estimated from one straingauge by assuming the axial force at the pile head (-1.7 m) to be that at the pile head (-1.0 m), because the other gauge didn’twork well. Although the values of earth pressure from the inclined setting earth presure cells, D4 and D6 were not symmetrical,the modified values of earth pressure in which the vertical component of earth pressure from D5 was removed, i.e., D4-D5/√2?and D6-D5/√2?, were almost symmetrical. So, it was found that the frictional resistance beneath the raft could be estimatedfrom the inclined setting earth pressure cells even though some error may be included.Figure 9 shows the relationship between the horizontal acceleration in X-direction and the shear force of pile C at the pilehead with spectra ratio. Figure 10 shows the relationship between the shear force at the pile head (-1.5 m) and the frictionalresistance beneath the raft ,（√2?×（D6-D4）/2×tributary area, 39 m 2）with spectra ratio. Here, phase difference zero meanspositive correlation and 180 degree means negative correlation. Phase difference is almost zero degree at a frequency from 1 to5 Hz.Inertial force of the building is apploximately estimated from multiplying the weight of the building by the horizontalacceleration of the building in Fig. 9. When the horizontal acceleration of the building is 0.3 m/s 2 and the vertical averageweight of the building is 159 kPa with the tributary area of pile C of 39 m 2 , the inertial horizontal force of the building aroudpile C is estimated to be 190 kN (=0.03/9.8×159×39). So, the lateral load sharing ratio of pile is estimated to be about 10 %when the shear force of the pile head is 20 kN.On another approach, the ratio of the lateral load carried by the pile can be directry esmitated from Fig. 10. When the shearforce of the pile is 20 kN, and frictional resistance beneath the raft is 100 kN, the lateral load shearing ratio of pile is estimatedto be 17 % (=20/(100+20)).Althogh the above consideration may include some error, it was confirmed that most of the inertial force of the building wastransfered to the subsoil through the raft.46