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 2014Tohoku Earthquake. These papers show the measured axial force and bending moment of the piles, earth pressure and porewaterpressure beneath the raft, and accelerations of the ground and the structure during the earthquake in which peak groundsurface acceleration was 1.75 m/s 2 . Moreover, simulation analyses of the seismic behavior of the building using a detailed threedimensional finite-element model were performed (Onimaru et al. 12）, Hamada et al. 13）, Hamada et al. 14）). The simulation resultsshow good agreement with the observed decrease in the input motion, which was reduced by the ground improvement, and theobserved increase in bending moments due to horizontal ground deformation.However, only a few case histories exist on the monitoring of the soil-pile-structure interaction behavior during earthquakes.The purpose of this study is to clarify the seismic performance of piled raft foundations based on seismic observation records.This paper presents seismic observation records on a piled raft foundation subjected to unsymmetrical earth pressure during theevents after the 2011 off the Pacific Coast of Tohoku Earthquake. Accelerations of the building, dynamic sectional forces of thepiles and dynamic earth pressure on both sides of the embedded foundation as well as that beneath the raft were observedduring 371 seismic events including an earthquake magnitude of Me7.1. Seismic observation period was from March 23 in2011 to April 30 in 2014. The maximum acceleration of 0.322 m/s 2 was observed at the foundation of building foundation.Based on the seismic records, it was confirmed that a lateral inertial force of the building was closely related to shear forcesand bending moments of the piles as well as frictional resistance beneath the raft. The ratio of the lateral load carried by thepiles was discussed comparing the observed shear force of the piles and the estimated inertial force of the building.The static and seismic observation records have been reported by Hamada et al. 15）. The results after June 2012 were added inthis paper and a seasonal variation of the long term static results were discussed.2 MONITORED BUILDING AND SOIL CONDITIONSThe seismically monitored building, which is seven-story residential building with three basement floors, is located inTokyo, Japan. The building subjected to unsymmetrical earth pressure is a reinforced concrete structure, 29.3 m high, with a71.4 m by 36.0 m footprint. Figure 1 shows a schematic view of the building and its foundation with a typical soil profile. Thesoil profile consists of fine sand layer just below the raft with SPT N-values from 10 to 20 and clay strata including humusbetween depths of 17 m and 24 m from the ground surface with unconfined compressive strength of about 140 kPa. Below thedepth of 24 m, there lies a diluvial fine sand layer with SPT N-values of 40 or higer. The shear wave velocities derived from aP-S logging system were about 200 m/s between the depths of 17 m and 24 m, and 480 to 570 m/s in the sand layers below theFig. 1 Schematic view of building and foundation with soil profile42