Damage Estimation of a Steel-Framed Building under Tsunami and Debris Flow

Abstract

　The Great East Japan Earthquake and the following tsunami which occurred on March 11th, 2011, caused a big disaster along the ocean-side of Tohoku area. The big tsunami carried different kinds of debris such as ships and cars up the stream, which caused additional damages to the buildings in the area. In this presentation, a finite element approach for damage estimation of a steel frame building under tsunami flow is described. A seismic wave recorded during the earthquake was first applied to the model, followed by an input of fluid forces due to tsunami wave. A three-dimensional free surface flow analysis code based on the volume of fluid (VOF) method was adopted to simulate wave propagation problems and to compare the obtained wave forces between several inflow conditions and building shapes. Then, a debris model with a velocity was collided, and the collapse behavior of the building was simulated using the adaptively shifted integration (ASI)-Gauss code. According to the numerical results, a wide area at the lower part of the building was highly pressurized for the model without openings, but the pressure was significantly reduced for the model with openings as the seawater flowed into the building. These results clearly showed the effect of wave force reduction by making large openings at lower parts of buildings. However, the openings may increase the possibility of debris colliding into the building, caused by the inflow motion of seawater into the openings. It was also shown that the estimated wave force could roughly approximate the stationary force acting on the surface of the building, while the simulated wave force obtained by the VOF method could consider both the impulsive peak and the stationary force. The behavior of the building under both wave forces was compared, and the effect of the impulsive wave on the building damage was confirmed. The interstory drift angle of the building was also drastically reduced by the openings at lower floors. Finally, a debris model constructed of six container boxes was introduced, and an impact analysis of the building was conducted. The impact phenomena and damage to the building were practically simulated. However, a change in the flow channel geometry according to current changes near the openings should be simulated in future investigations to consider a more precise flow path of tsunami debris.