There were several cases reported where buildings had to stop functioning normally because of the damage to foundations during the 2011 Great East Japan earthquake. The authors carried out static analyses using a foundation structure model in order to investigate the cause of damage to pile foundations by focusing on three typical buildings. Lateral load at pile head and differential movement of soils were estimated based on a seismic response analysis by using recorded ground motions of the 2011 Great East Japan earthquake and by looking into the soil profiles and structural characteristics of buildings. Load-deformation characteristics of pile elements and soil springs were formulated so that the model can incorporate nonlinear behaviors. Results obtained from the analysis explain fairly well the actual damage of pile foundations. It was confirmed that a controlling factor causing damage to pile foundations is the existence of soft soils and the variation of surface soil layers. The proposed procedure can be considered as a practical seismic design method of foundations that ensures a required performance for large earthquakes.
