7th International Conference on
Protection of Structures against Hazards
30-31 October 2018, Hanoi, Vietnam

COLLAPSE ANALYSIS OF A STEEL FRAME BUILDING UNDERTSUNAMI FLOW
Daigoro Isobe* and Seizo Tanaka**

University of Tsukuba
1-1-1, Tennodai, Tsukuba-shi, Ibaraki, 305-8573, Japane-mail: <isobe@kz.tsukuba.ac.jp>
webpage: http://www.kz.tsukuba.ac.jp/~isobe/index.html

Keywords: Collapse analysis, fluid analysis, steel-framed building, tsunami, VOF
method, ASI-Gauss code

Abstract. The Great East Japan Earthquake and the following tsunami thatoccurred on March 11, 2011 caused a significant disaster along the ocean-side of
the Tohoku area. The big tsunami carried different kinds of debris such as ships
and cars up the stream, which caused additional damage to the buildings in thearea. In this paper, a finite element approach for the damage estimation of asteel-framed 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 owing to the 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 compare the obtained wave forces between several
inflow conditions and building shapes. Then, a debris model with a velocity wascollided, and the collapse behavior of the building was simulated using theadaptively shifted integration (ASI)-Gauss code.
1INTRODUCTION

A huge disaster occurred after the Great East Japan Earthquake on March 11, 2011, when thefollowing big tsunami washed away most of the manmade structures in its way. The design andconstruction of tsunami evacuation buildings started soon after the event, particularly in areas
where no other natural evacuation points were in the vicinity.
In this paper, the wave forces owing to a tsunami acting on the surface of a building wereevaluated by fluid analysis using the finite element method (FEM). Then, a one-way coupling
analysis of a steel-framed building by continuously applying a seismic excitation, buoyant force,and tsunami force in a single simulation was conducted.
There were also some possibilities that the flow of debris such as ships, cars, and containers
may had caused some destructive impact and additional damage to buildings 1 . Therefore,evacuation buildings should be designed not only to withstand seismic excitations and tsunami
waves but also to cope with impacts caused by debris. A continuous simulation with some debris
collided after the application of wave forces is also conducted in this research.

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Daigoro Isobe and Seizo Tanaka

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FLUID ANALYSIS USING STABILIZED FEM

A numerical code2 using stabilized FEM based upon the volume of fluid (VOF) method, whichindirectly expresses a free-surface shape by function values, was adopted for the fluid analysis. A
hybrid parallel computing method was implemented in this code to drastically reduce thecomputational time and memory resources to cope with large-scale simulations.
A numerical model with a region of 240 m in length, 180 m in width, and 80 m in height wasconstructed. Two types of building models without any openings and with openings wereconstructed and the pressure distributions at front of the models were compared. The buildingwith openings was designed for evacuation uses3 and was 10 stories high, with 40.15 m of heightand 32.00 m of width. The buildings were modeled as rigid bodies that allowed no deformation,and the openings were assumed to be located at the window parts. These models were all
subdivided with tetrahedron elements, with the distances between nodes fixed at approximately
0.5 m under the waterline and around the building. The total number of nodes and elements wereapproximately 3.7 million and 21 million for the model with openings.
The shape of the flow surface and the pressure distribution computed at the front of thebuilding are shown in Figure 1 for the model with openings. The upstream depth was set to 8.0 m
and the tsunami wave velocity to 12.0 m/s in this case. One can observe the inflow andpropagation of the tsunami wave, and the impact to the front of the building. The complex freesurface shape owing to amplification of the wave height by short reflected waves, for example,appears to be well simulated. The seawater flowing in and out of the openings can also beobserved.
[kPa](a) 10 s[kPa](b) 20 s
Figure 1: Shape of flow surface (left) and pressure distribution at front ofbuilding (right) [model with openings]
3DEBRIS IMPACT ANALYSIS OF TSUNAMI EVACUATION BUILDING

A one-way coupling analysis of the fluid and structure was conducted using the simulated wave
force obtained from the fluid analysis. Then, the behavior of the building was simulated using theadaptively shifted integration (ASI)-Gauss code 4 when an initial velocity was applied to somecontainer boxes that mimicked the debris owing to the tsunami (Figure 2). The container boxes collide
near the beam-column joint sections of the second and third floors, causing ultimate material failures
to columns and beams around the impact point. The shock wave rapidly propagating from the impact
point can also be observed. The relative velocity between the debris and tsunami flow increases when
the debris reduces its velocity in front of the building. Then, a much larger drag force is applied to thedebris, and thereby to the building itself. Member fractures initiate at the front columns of the first floorand propagate progressively to the inside. Finally, the building collapses and is washed away.

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Daigoro Isobe and Seizo Tanaka
Yield function value
fyflow(a) 0.0 s (on impact)(b) 0.8 s(c) 2.3 s(d) 3.2 s(e) 4.2 s(f) 4.7 s

Figure 2: Behavior of building during debris collision
4CONCLUSIONSIn this paper, a fluid analysis using a stabilized FEM was described. The differences of thefree-surface shapes and tsunami wave forces between models with and without openings are to
be shown in the presentation. 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 withopenings as the seawater flowed into the building. These results clearly showed the effect ofwave force reduction by making large openings at lower parts of buildings.
Furthermore, 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 werepractically 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. The demand for a more advanced, two-way coupling analysis
between the fluid and structure is now growing.
REFERENCES[1]

National Institute for Land and Infrastructure Management (NILIM): Report on Field Surveys andSubsequent Investigations of Building Damage Following the 2011 Off the Pacific Coast ofTohoku Earthquake, Technical Note of National Institute for Land and Infrastructure Management
No. 636, Building Research Data No. 132, 2011, in Japanese.

[2]

S. Tanaka, F. Sun, M. Hori, T. Ichimura and M.L.L. Wijerathne: Large-scale Failure Analysis ofReinforced Concrete Structure by Tsunami Wave Force, 15th World Conference in Earthquake
Engineering (15WCEE), CD-ROM, Lisbon, Portugal, 2012.

[3]

National Institute for Land and Infrastructure Management (NILIM): Practical Guide on
Requirement for Structural Design of Tsunami Evacuation Buildings, Technical Note of National
Institute for Land and Infrastructure Management No. 673, 2012, in Japanese.

[4]

D. Isobe: Progressive Collapse Analysis of Structures: Numerical Codes and Applications,Elsevier, eBook ISBN: 9780128130421, Paperback ISBN: 9780128129753, 2017.

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