Research Trends and Results

Features of tsunami action on highway bridges by theGreat East Japan Earthquake
KATAOKA Shojiro (Ph.D.), Senior Researcher
KANEKO Masahiro, HeadNAGAYA Kazuzhiro, Senior Researcher
Earthquake Disaster Prevention Division, Research Center for Disaster Management
the Great East Japan Earthquake、tsunami action、highway bridge

2.5
Superstructurewashed out
上部構造流出Superstructure survived
流出せず

2.0
Horizontal force / capacity
水平波力／抵抗力
Vertical force / capacity
鉛直波力／抵抗力

1.5
1.0

Katagishi-ohashi #1

Katagishi-ohashi #2

Shin-Kitagami-ohashi #2

Utatsu-ohashi #3

Utatsu-ohashi #4

Yanoura

Kawaharagawa

Nijuichihama

Shin-Kitagami-ohashi #1

Utatsu-ohashi #1

Utatsu-ohashi #2

Kesen-ohashi #1

Kesen-ohashi #2

Numata overpass #2

Koizumi-ohashi

0.0

Shin-aikawa

0.5

Numata overpass #1

波力－抵抗力比/ Capacity ratio
Wave force

1.Introduction
Damage to many bridges by the 2011 Tohoku
tsunami, especially the flow out of superstructures,caused harmful effects in the disaster area. As a part ofa research project to formulate design tsunami action
for highway bridges, a tsunami numerical simulation
was performed to investigate features of tsunami action
on highway bridges. The simulation result is examinedby comparing estimated wave force acting onsuperstructures and their loading capacities1).
2. Features of tsunami acting on highway bridges
Propagation and run-up of the 2011 Tohoku
tsunami were simulated using 2-D FDM, based on thenonlinear long wave theory, in order to evaluate time
histories of wave height and flow velocity at 10 bridge
sites. Horizontal and uplift forces acting on thesuperstructures due to the simulated tsunami were thenanalyzed using the numerical wave flume1), i.e. anumerical analysis model used to conduct hydraulicmodel experiments by numerical simulations.
Figure 1 shows the ratios of horizontal force tohorizontal capacity and vertical force to vertical
capacity of superstructures of highway bridges. The
capacities were estimated from the ultimate capacity ofbearings and weight of superstructures. We can seethat at least one of the horizontal and vertical wave
force-capacity ratios of the superstructures that werewashed out are larger than 1, except for theKoizumi-ohashi Bridge, while both the horizontal andvertical ratios of the superstructures that survived aresmaller than 1. As for the Koizumi-ohashi Bridge, theprocess of its superstructure washout was reproduced bya detailed earthquake-tsunami damage simulation, taking
account of effects of strong motion and rupturing
sequence of its bearings.
Since the wave force-capacity ratios account for thedamage status as described above, the simulated tsunami
at the bridge sites are considered to be reliable. Figure 2
shows time histories of tsunami inundation height at thebridge sites. The speed the water surface rose is around 1
to 5 m a minute at these sites; the tsunami is not likely to
be a bore-type one but one that gradual raises the watersurface.

小 新 沼 沼 気 気 歌 歌 新 二 矢 川 歌 歌 新 片 片
泉 相 田 田 仙 仙 津 津 北 十 の 原 津 津 北 岸 岸
大 川 跨 跨 大 大 大 大 上 一 浦 川 大 大 上 大 大
橋 橋 線 線 橋 橋 橋 橋 大 浜 橋 橋 橋 橋 大 橋 橋③ ④ 橋 ① ②橋 橋 ① ② ① ② 橋 橋① ②①②Figure 1 Wave force/capacity ratio of superstructures
Rise speed of water surface浸水深(m)height (m)Inundation(Key words)

5m

20.0

2m

1m/min

15.0
10.0
5.0
0.0
-5.00

20

時間(分)
Time(min.)

4060

Koizumi小泉大橋
Shin-aikawa
新相川橋
Yanoura矢の浦橋
Numataov
沼田跨線橋
Kawaharagawa
川原川橋
Nujuichihama
二十一浜橋
Shin-Kitagami
新北上大橋
Katagishi
片岸大橋
Kesen
気仙大橋
Utatsu歌津大橋

Figure 2 Time histories of inundation height at bridge sites
Peak flow velocity of the simulated tsunami is around
6 to 8 m/s, which coincides with the average subaerial
flow velocity, about 6m/s, estimated from debris
movement recorded in video shots.
3.Ongoing and future actions
Further research has been conducted to reliably
formulate tsunami action for design practice based on thefeatures of the tsunami from the Tohoku event as well as
anticipated future giant earthquakes.
[Sources]
1) Estimation of wave force acting on bridge
superstructures due to the 2011 Tohoku tsunami, Journalof Disaster Research, Vol. 8, No. 4, pp. 605-611, 2013.8.