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.