Lessons From the 2011 Great East Japan Earthquake Focused on Building Damage

Abstract eng:
A huge earthquake with the magnitude of 9.0 occurred in the Pacific Ocean off the coast of Tohoku district, Japan on March 11, 2011 (indicated as “the 2011 Great East Japan earthquake” hereafter) and caused huge physical damage and loss of life. The magnitude of this earthquake is the largest recorded in Japan since modern seismograms became available. The huge earthquake caused not only tremendous tsunami damage but also structural damage due to the severe ground motions with a long duration. This paper describes the lessons from the 2011 Great East Japan earthquake, focused on the building damage, in relation to the observed ground motion characteristics from the engineering view points for countermeasures against the expected earthquakes in other area of Japan and also in foreign countries. First, the following observed ground motion characteristics are addressed. 1) The observed high acceleration record at a K-NET site (MYG004) with maximum acceleration of 2,700 cm/s2 comprising high frequency content is investigated. It is found that the ground motion has no power to collapse houses and also topple the unfixed book. 2) Impact of long-duration motions focused on the cumulative responses of base-isolated buildings using K-NET (MYG006) data for not only main shock but also aftershocks and past earthquakes. It is found that cumulative response due to many past earthquakes is larger than that of main shock of the huge earthquake. Difference of the cumulative response due to geological structure in Kanto Basin is quantitatively investigated. 3) Site dependent ground characteristics with 3 times the difference in PGAs and PGVs based on observation data in Sendai City. Soil amplification should be enforced in seismic design possibly including seismic micro-zoning. Then, the following specific features of building damage including housing land damage are addressed. 1) Damage features of the retrofitted 9-story SRC building at Aobayama campus of Tohoku University is investigated. Ground motion amplification in the hilly zone and the induced resonance phenomena is strongly related to the severe damage considering the non-stationary nature of ground motion and the nonlinearity of the building. 2) Foundation damage of the two pile foundation buildings damaged during the 1978 Miyagi-ken Oki earthquake is described together with other damaged pile foundation buildings. The two buildings were divided, black and white, during the 2011 Great East Japan earthquake due to after treatments of the 1978 earthquake. Balance of foundation and the superstructure is needed for the synthetic seismic performance of the whole building to be achieved. 3) Non-structural element and equipment damage are described. Ceiling board damage occurred at many multi-purpose halls, local governments’ halls and shopping centers, which caused human damage. It is needed to establish total balance of the structural elements, the non-structural elements, and the equipment. 4) The huge number of housing land damaged in Sendai City is described. The damage is caused by the valley-filled land with high water level and the ground motions with long-duration. Finally concluding remarks are described including above findings.

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