A Study on Dynamic Behaviors of a Building on Liquefied Ground Based on Earthquake Observation Records of Building and Ground

Abstract

This paper describes liquefaction response behaviors for foreshock, main shock and aftershocks of the 2011 Off the Pacific Coast of Tohoku Earthquake. Based on analyses of seismic observation records at a plate-shaped building constructed in the liquefied area at Chiba City of Chiba Prefecture, it focuses on change of properties of waveform at the ground surface and change of predominant frequencies of a soil-pile-foundation-superstructure system with spectral ratio of building to ground. The results of study were recognized following phenomena;

1) A liquefaction phenomenon occurred on the main shock and the maximum aftershock from ground records. From change of predominant frequencies of a soil-pile-foundation-superstructure system, the soil stiffness was almost recovered two hours after the maximum aftershock, which means an excess pore water pressure became low.

2) On the main shock and the maximum aftershock, predominant frequencies of a soil-pile-foundation-superstructure system were low and spectral ratio amplitude of building to ground was small, due to liquefaction phenomenon.