Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, JapanDAMAGE ANALYSIS OF BRIDGES AFFECTED BYTSUNAMI DUE TO GREAT EAST JAPAN
EARTHQUAKE
Kenji KOSA1
1

Professor, Department of Civil Engineering, Kyushu Institute of Technology,
Kitakyushu, Japan, kosa@civil.kyutech.ac.jp

ABSTRACT: The Great East Japan Earthquake and the resulting tsunami hit the coastal
areas of Japan. It is found that the outflow of steel and steel truss bridges is more serious
than concrete bridges. By the use of videos, the tsunami velocities in 5 severely affectedareas were estimated and the overall average is about 6.0m/s. In Rikuzentakata, 30% RC
buildings suffered structural damage and 40% bridges flowed out. Besides, it is foundthat the outflow of superstructure is able to be judged by the level of ratio β between
superstructure resistance and wave horizontal force primarily.
Key Words: tsunami, bridge damage, tsunami velocity, building damage

INTRODUCTION
During the Great East Earthquake, the outflow of superstructure and excessive scour occurred to morethan 300 bridges in East Japan. Fig. 1 illustrate the bridges which suffered damage Rank A (bridge
seriously damaged and could not be used). Among the 300 bridges, 9 national way bridges, 14
prefectural road bridges and 101 railway bridges, suffered serious losses. Despite a lack of official data
about the damage to city and village roads, by the use of Google Earth, it is noted that at least 200
bridges suffered serious losses.
Furthermore, the damage extent of bridges in East Japan is compared with the damage to bridges
caused by Sumatra Earthquake. Before comparison, we define the damage level in Table 1, focusing
on the outflow condition of bridge superstructure. The damage level of 29 different bridge
superstructures affected by tsunami in Great East Japan Earthquake is plotted in Fig. 2-A and thedamage level of 26 bridge superstructures affected by tsunami in Sumatra Earthquake is illustrated inFig. 2-B. From the 2 figures, it is found that the bridges constructed by steel or steel truss suffered
more serious damage than concrete bridges. All the 6 survey steel and steel truss bridges flowed out by
tsunami. For the concrete bridges, during the 2 tsunami disaster, about half PC superstructures belong
to Rank A while about 2/3 RC superstructures belong to Rank A.
EVALUATION OF TSUNAMI VELOCITY
Based on former research, in order to analyze the tsunami action on bridge superstructures, it isnecessary to estimate the tsunami flow velocity. In this chapter, we apply the videos recording the1386Prefectural Road National Road
Total number ofbridges washed away

14 9
Railroad
101

More than 324

Table 1 Definition of damage level
Outflow condition ofsuperstructure

Damage level

More than
200

City or Town Road

Rank A

Flowed out completely

Rank B

M oved but not divorced fromabutment

Rank C

Slight damage

Fig. 1 Amount of bridges washed away
18

Rank A

Rank C

12

14
12

Superstructure Number

Superstructure Number

16

8

10

8
6
4

9

2

PC

RC

1

Steel

1
6
3
0

Steel truss

Rank B

Rank C

9

5

2
0

4

Rank A

A. Damage in East Japan

3

4
PC

5

1

2

6

2

1
1

RC
Steel
B. Damage in Sumatra

Steel struss

Fig. 2 Comparison of tsunami damage
tsunami flood on land, to estimate the tsunami velocity comprehensively. And in order to exclude theaccidental case, 5 typical tsunami affecting areas are selected to carry out velocity measurement.
Method of Velocity Estimation
During tsunami landing, some videos were shot. It is possible to apply the videos to estimate thetsunami velocity.
After tsunami attacking, some houses or barges were swept off and became the floating debris. In
video record, it is able to search for 2 distinguished field points where a piece of floating debris, suchas moving house, barge or front part of tsunami, passed through. By using the Google Earth’s distancemeasurer and the seconds counter, it is available to obtain the distance between the 2 points and thetime span for the floating debris flowed from one point to the other. Then by using Eq. 1, the velocity
of debris was computed and this velocity is assumed as the tsunami velocity.

v l /t(1)

in which, v is the tsunami velocity (m/s); l is the distance between 2 field points (m); t is the time spanfor debris flowed between 2 points (s).
Velocity Result
Herein, the detailed measurement in Shizugawa town of Minamisanriku city is described as an

1387

11

Tsunami velocity [m/s]

10
9
8
7
6

(a) Shizugawa (c) Rikuzentakata (e) Wakabayashi
Max Overall avg
Table 2 Tsunami velocity in Shizugawa
Akita(b) Otsuchi(d) ShinkitakamiMinAvg(b) Otsuchi
Iwate
Prefecture
9.0
Prefecture
Distance Time Velocity
Position No. Debris
7.8[m][s] 7.5 [m/s]6.3(c) Rikuzentakata
7.0
5.9
1
House 7.0 45
8
5.6
6.1
(a) Shizugawa

Miyagi5.8
Prefecture

5 Yamagata

4 Prefecture
3
2
1
0

5.6

5.7

(d) Shinkitakami
4.1(e) Wakabayashi
1 2

Fukushima (a)Prefecture

House

37

8

4.6

3

Vehicle

111

21

5.3
5.9

House

63

6

Ship

57

7

House

57

House

39

House

4
5

Pacific Ocean

1 2 3 4 5 5 7 8 9 102

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

(b)

(c) 8
9

Fig. 5 Maximum, minimum and averagevelocities
10
House
Fig. 3 Tsunami velocity estimate positions
Average velocity
Tsunami direction
Building area

Hill district
Sloping dike
Position No.

Shizugawajunior middle
school

A1

1
2
3

4

Shizugawa senior
middle school
A2

Hachimangawa
Bridge

8
9
10

Ot
s
Ri uchiverKozRi uch
ve i
r

14

km

3
3.4
1

ami
Kitak r
v
i
R e

2
3
4

3.4km
(a) Shizugawa

13

6.4

14

6.4

1 2 3 4
(d)

1 2 3

58

9

4.3

161

25

4.1

5
3

6
7

4

8

Kawahara
River

e bu

ik
No d

12
11

ilt

10
9
260m

(b) Otsuchi

Shinkitakami
Bridge

7.8

5.8

460m

7
5
6
A3

2

6.6

6.3 (e)

1

Kesen
River

2.7

6

10

5

2

15 13
1

5.3

5.0 40Unknown(c) RikuzentakataNa
Ri toriverYuriage
Bridge123750m(d) Shinkitakami(e) Wakabayashi

Fig. 4 Velocity result
example.
In Shizugawa, 2 videos made at junior and senior schools are able to be used for the estimation oftsunami velocity. By using the method in last section, the velocity is measured by 10 times at different
positions, which are plotted in Fig. 4-(a). Among the 10 positions, No.1~4, No.5~7 and No.8~10
locate at A1, A2 and A3 areas respectively. Table 2 plots the debris types and velocity result in
Shizugawa. The average velocity in Shizugawa is 5.8m/s.
By the same process, the tsunami velocities in Otsuchi, Rikuzentakata, Shinkitakami and
Wakabayashi have been estimated and the measure positions are illustrated in Fig. 4-(b) to (e). The
velocities of each measure position and the maximum, minimum and average velocities in each area

1388

11

Tsunami velocity [m/s]

10

Max
Min

Overall avg
Avg(a) Shizugawa (c) Rikuzentakata (e) Wakabayashi(b) Otsuchi(d) Shinkitakami

9.0

9

7.8

8

7.5

5.9

7
6
5

6.1

5.0

4.1

3

0

5.3

5.9

2.7

2
1

7.0

6.1

5.7

5.8

4

6.3

7.0

1 2 3 4 5 5 7 8 9 10

1 2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

1 2 3 4

1 2 3

(a)

(b)

(c)

(d)

(e)

Fig. 5 Maximum, minimum and average velocities
are given in Fig. 5. The overall average is 6.1m/s. It is obvious that the average velocities in
Shizugawa, Otsuchi and Wakabayashi have the same level (about 6.0m/s) and are close to the overall
average. In addition, the average velocities in Rikuzentakata is greater while in Shinkitakami issmaller than the overall average.
DAMAGE TO STRUCTURES
Soon after the great earthquake, the authors conducted several field investigations to the disaster areasof Japan. In this chapter, as a specific example, the authors will analyze the damage conditions ofstructures including residential buildings and bridges in the Rikuzentakata region (Iwate Prefecture),
which is one of the nearest areas to the epicenter and has suffered great tsunami with the inundation
height as about 15m. The tsunami affecting area (Japan Institute of Construction Engineering 2011) is
illustrated in Fig. 6. Total 26 bridges over the main rivers and original 628 residential buildings in one
central area (circled with long dash line) will be analyzed for their damage conditions in detail.

Tsunami affecting area
Survey area ofresidential buildings
Bridge (Rank A)
Bridge (Rank C)
N
Kesen
River
Kawahara
River
Kesen
Bridge500m

Numatakosen Bridge
Kawahara
BridgeHamadaBridgeHiroda Bay

Fig. 6 Research region of Rikuzentakata

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Table 3 Damage extent of buildings
DamageextentDefinition

A

Significant
structural damage

B

Non-structural
damage onlyC

Slight damage(concrete spall)Rank A

Rank B

3(19%)

Rank C

5
(31%)

8
(50%)

220m

Survey area
(RC Building)
Rank A
Rank B
Rank CN
Rikuzentakata
City Office

(3)
(4)

(2)

(a). RC buildings

TakataStreetKawahara
River
Stream612(100%)(1)(b). Timber buildings

Furukawa
Pond

Fig. 7 Investigation result of buildings

Fig. 8 Survey area to buildings

Damage to residential buildings
Authors decided the survey area for residential buildings as illustrated in Fig. 6 and enlarged in Fig. 8.
With relatively flat terrain and being close to the coastline, the survey area which is outlined by the
Kawahara River, Takata Street, a small stream and the bank of Furukawa Pond suffered most severe
damage. Buildings in this area are simply divided into two types: reinforced concrete building (RCbuilding for short, including steel-frame building) and timber building.
Authors defined the damage extents of residential buildings as presented in Table 3. In Fig. 7,
among total 16 RC buildings, proportion is 31%, 50% and 19% for Rank A, B and C, respectively.
70% of RC buildings suffered non-structural damage (sum of Rank B and C buildings), whichsuggests the great resistance to tsunami impact. Further, all 612 timber buildings are washed away orcrashed into pieces by tsunami effect (Rank A), from which, timber building is considered not suitablefor future design of anti-tsunami building.
Fig. 8 presents the distributions of RC buildings in survey area. Compared with Rank B and Rank
C buildings, there is the trend that Rank A buildings are relatively in smaller size which makes thebuilding with smaller stiffness to resist tsunami impact. Further, Rank A buildings are mainly
distributing in regions relatively closer to the coastline.
To introduce the detailed damage performances of RC buildings, one typical building is selected
for each damage rank with their photos shown in Photo 1 and Photo 2. Positions can be referred from
Fig. 8. Typical Rank A building is a two-floor, steel-frame structure with its structural members
seriously damaged. Main columns of left side in second floor were washed away and beams inhorizontal direction suffered seriously flexural damage and gathered to residual frame at right side;
side walls of it have all been washed away; Typical Rank B building is a reinforced concrete building
with its non-bearing wall in the first floor damaged; great lateral load of tsunami impact probably
caused it; typical Rank C building (building (3)) is also a reinforced concrete building with relatively
smaller size. Since building (4) (Fig. 8) with greater size in front of it worked as barrier and weakened

1390

(1)

(2)

Collapse of 2nd floor

Damage of non-bearing wall

Rank A

Rank B

Photo 1 Damage performance of buildings (Rank A, Rank B)

Rank A(3)

16(61.5%)

Rank B

Rank C1510(43%)(38.5%)

No obvious damage
Rank C

Photo 2 Damage performance of buildings (Rank C)

Fig. 9 Investigation result of bridges

the impact, building (3) did not suffer great damage.
Damage to bridges
Damage to bridge is also analyzed by the authors. Same with the former description, as superstructureof a bridge is of great significance for the normal passage, the damage extent for bridges are divided
by the outflow conditions of superstructure. Rank A means the superstructure flowed out completelyby the impact of tsunami, which makes the bridge cannot be used; Rank B refers that the tsunami
impact causes the superstructure to have relative movement from abutment or pier while is still
passable; Rank C means the damage mainly occurred to the attached elements of bridge like the coverconcrete or the hand rails.
From the investigation of authors and also combined with the satellite photographs, the damage
conditions of the main 26 bridges in the tsunami affecting area are evaluated, of which the results foreach bridge can be referred from Fig. 6.
From Fig. 6, the authors found 80% bridges in the Kesen River suffered Rank A damage (4 in all 5
bridges); while only 18% bridges in the Kawahara River (2 in all 11 bridges). By using distancemeasurement function of Google Earth, Kensen River has greater size (width in level of 120m) than
Kawahara River (width in level of 15m). Direct run-up of tsunami in the greater size river isconsidered as the reason for more serious damages of related bridges.

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As illustrated in Fig. 9, the damage conditions for the surveyed bridges are apparently divided into
Rank A and Rank C, with Rank A taking the share of around 39% (10 among all the 26 bridges) while
Rank C taking the share of around 62% (16 among all 26 bridges).
Table 4 Bridge details in Rikuzentakata area
Damage Span Length Width
Rank
L[m]
B[m]

D[m]

Drag
Coefficient
Cd

2.59

1.58

HeightBridge Name

Span
AmountGirder Type

Numatakosen

3

PC-T girder

Kawahara

1

PC hollow girder

C

28.80

14.80

1.77

Kesen
Hamada5
1

Continuous steel girder
PC-T girder

AC

181.05
22.50

13.30
14.80

2.67
1.72

A

20.00

13.50

Dead Load
W[kN]

β

3400

1.34

1.30

8800

4.30

1.60
1.30

23800
4100

0.99
2.64

JUDGEMENT FOR BRIDGE LOSSIn this chapter, the authors will use a simplified equation to judge the outflow condition forsuperstructure of bridge. Based on the possessed bridge drawings, the judgment is conducted to 4
bridges (names and positions can be referred from Table 4 and Fig. 6) in Rikuzentakata region andanother 25 bridges in the entire Tohoku area.
The tsunami impact force and resistance of superstructure can be computed by Eq. 2 and Eq. 3:
1
F  wCd v2 Ah2
S  W(2)(3)

in which, F is tsunami impact force; ρw is density of water (1030kg/m3); Cd is drag coefficient with its
value decided from reference (Japan Road Association 2002); v is tsunami velocity and Ah is effective
projected area of the superstructure in horizontal direction; S is resistance of superstructure; μ is
friction coefficient used as 0.6 (Rabbat, et al. 1985); W is dead load of the superstructure.
Thus, an indicator is defined as Eq. 4:



S
F

(4)

in which, if β ratio is smaller (greater) than 1.0, resistance of superstructure is smaller (greater) thantsunami impact force, which means superstructure is easy (difficult) to outflow. For the tsunami
velocity (v) in Eq. 2, based on measured results described previously, the average value for entire
Tohoku area is around 6.0m/s. Thus, v as 6.0m/s will be used as a constant to all bridges, for only
concentrating on the relationship between damage conditions with the horizontal force.
Fig. 10 illustrates the relationship between the computed β ratios (from bridge details in Table 4)
with the damage conditions. In terms with the two Rank C bridges, β ratios are all greater than 1.0
with average as 3.47, which means resistance is greater than tsunami impact force. Thus, theirsuperstructure survived. For Rank A bridges, the β ratio is 0.99 and 1.34, respectively (average as1.17). Average β ratio of Rank C bridges is 2.97 times of Rank A bridges.
Computed β ratios for bridges in entire Tohoku area (total 29 bridges, Rikuzentakata area included)
are presented in Fig. 11. Average β ratio of Rank A bridges with their superstructures outflowed is 0.87.
Average β ratio of Rank C bridges with their superstructures survived is 1.91 (2.20 times of Rank A).

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5.00

5.00

4.30

4.00

=S/F

6.00

Numatakosen
Kawahara
Kesen
Hamada4.00

Avg: 3.47

3.00

3.00

2.64

2.00

2.00
1.34
1.00 Avg: 1.17
0.00

Concrete girder
Steel girder

β=S/F

6.00

Avg: 0.90

1.00

0.99

Rank A

Avg:1.91
Max:1.38

0Rank C

Fig. 10 β Ratios for Rikuzentakata area

Min:0.63
Concrete SteelConcrete Steel

Rank A

Rank C

Fig. 11 β Ratios for Tohoku area

With respect to β ratios of different girder types (simply divide into concrete girder and steel girder,
Fig. 11), concrete girders have relatively great β ratios and 53% of them have survived (12 among total
23, Rank C); all the steel girders have relatively small β ratios and have flowed out (Rank A), inferring
the small resistance to the tsunami impact.
From the computation results, difference of β ratios between Rank C and Rank A bridges are
obvious. Trend of β ratios can fit the damage conditions well. As a result, β ratio is considered as aneffective indicator to judge outflow of superstructure. However, as velocities in all areas probably not
uniform to be 6.0m/s as the authors assumed. Some β ratios of Rank A bridges are greater than 1.0(like Numatakosen Bridge, Fig. 10) while some of Rank C bridges are smaller than 1.0.
TSUNAMI VELOCITY IN RIKUZENTAKATA
For the damage analysis on structures like the judgment of bridge loss conducted in Chap. 3, it is ofgreat significance to get the tsunami velocity. In this chapter, two methods will be applied to evaluate
tsunami velocity in Rikuzentakata.
Same with what have been explained in the former content, first method is based on the recorded
videos. Based on possessed materials, three videos shot in Rikuzentakata region is considered suitableto evaluate.
The evaluation positions are plotted in Fig. 13. Table 5 presents calculation parameters for total 15
groups of evaluated velocities. Average values of each sub-area are in the range from 5.29m/s to
8.50m/s.
With respect to the second evaluation method, the following equations which are based on theformer research (Matsutomi, H. 1998).

u /(gR)0.5  {2Cv2 Fr2 /(Fr2  2Cv2 )}0.5 (hf / R)0.5(5)u  0.58( ghf )0.5

(6)

1393

Table 5 Tsunami velocity by videos
l
t
(m)
(s)
1
House
98.30 14.00
2
House
70.70 10.00(a)No.1
Junior High 3
House
58.40 9.00
School4
House72.70 10.00
5House
78.97 10.00
6 Wavefront 108.08 13.00(b)Kesen
7 Wavefront 35.92 4.00
River
8 Wavefront 41.04 5.00
9Boat
26.73 4.00(c)Minshuku
10 Broken Tree 16.34 2.50
Yoshida11 Broken Tree 27.56 3.90(d)Telecom
12 Wavefront 50.67 7.00
Machine.Ltd
13House
32.35 6.10(e)Suwa
14House
32.35 5.80
Shrine15House32.35 6.50
PositionNo.

Debris

Tsunami directionv
Avg.
(m/s) (m/s)
7.02
7.07
6.49 7.15
7.27
7.90
8.31
8.98 8.50
8.21
6.68
6.54 6.76
7.07
7.24 7.24

hf hf

TP

R

hr

h

Land

Fig. 12 Factors for equation
Table 6 Tsunami velocity by equationh f ' (m)h (m)h f (m)v (m/s)A Roadside Station 15.20

-0.59

15.79

7.21

B

15.80

-0.59

16.39

7.35

14.53

4.13

10.40

5.86

14.87

2.67

12.20

6.34

No.

C

5.30
5.58 5.29
4.98

Building

D

Building Name
Capital HotelSea and Shell
MuseumTeijyusokushin
House

in which, u is the tsunami velocity; hf and hr are the inundation depth in front and behind of thebuilding, respectively; R is the tsunami run-up height; Cv is the velocity coefficient; Fr is the Froudenumber; g is the gravity acceleration (9.8m/s2). Some of the parameters are illustrated in Fig. 12.
By eliminating the same parameter R in the two side of the Eq. 5, the only two unknown
parameters are the Froude number (Fr) and velocity coefficient (Cv). Cv value is chosen as 0.9 based on
experimental result (Matsutomi, H. 1998), while Fr number is given as 0.65 for the Rikuzentakata
region by the investigation report (Institute of Industrial Science 2011). Thus, based on Eq. 5, theavailable equation for computing tsunami velocity is derived to be Eq. 6.
As illustrated in Fig. 12, hf’ is the inundation elevation (front of building, from TP level). h isground height (ground settlement by earthquake included, from TP level). Values of these twoparameters can be obtained based on reference (The 2011 Tohoku Earthquake Tsunami Joint Survey
Group 2011). Thus, based on the inundation depth hf (difference of hf’ and h), velocities near fourbuildings (positions shown in Fig. 13) can be calculated from Eq. 6. Table 6 shows calculation
parameters and results. From Fig. 13, evaluated tsunami velocities from equation can roughly coincidewith those in neighboring areas from videos. (A B with (d), C D with (c), Fig. 13)
Thus, focus on evaluated results from videos as illustrated in Table 5 and Fig. 13, the average
tsunami velocity for Rikuzentakata is about 7.0m/s, being greater than 6.0m/s of entire Tohoku area.
RECALCULATION OF β RATIOS BY DETAILED VELOCITIESAs explained in the former chapter, tsunami velocities in all areas were not uniform to be 6.0m/s as theauthors assumed. Some β ratios of Rank A bridges are relatively great while some of Rank C bridges
are small. Thus, based on the detailed tsunami velocities obtained in the previous chapters, the β ratios
for four bridges in Rikuzentakata and another eight bridges of other velocity measured areas wererecalculated.

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Recalculation for Rikuzentakata area
Based on the distribution of measured tsunami velocities as shown in Fig. 13, the detailed velocity
near each bridge is used for recalculation. For Kesen Bridge, the average velocity 8.50m/s in (b) riverarea is applied; for Kawahara Bridge, the average velocity 7.28m/s of A and B points is applied; for
Hamada Bridge, the average velocity 6.10m/s of C and D points is used; and for Numatakosen Bridge,
the average velocity 6.76m/s in the (c) area is used.
Thus, using the same calculation methods and the detailed velocities, the β ratios for Rikuzentakata
area are recalculated and illustrated in Fig. 14.
From Video
From Equation

1

Tsunami Direction
Bridge Position52
Kesen River
6
7

N

3
4
(a)Avg:7.15(b)Avg:8.50
8Kawahara
River
12

Kawahara
BridgeB:7.35

A:7.21(d) 7.24

Kesen
BridgeSection viewFig.11 (a)

a

at
Tak

a
bar

tsu
ma

Numatakosen Bridge

HamadaBridgeC:5.86(e)Avg:5.29
15 14 13

D:6.3411 10
9(c)Avg:6.76

Seawall

Section viewFig.11 (b)Hiroda Bay

260m

Fig. 13 Distribution of tsunami velocity
For the Numatakosen Bridge (Rank A damage), which originally has relatively greater β ratio(1.34), the β ratio reduces to be 1.06, indicating the smaller girder resistance. For the Kesen Bridge, as
the greater tsunami velocity in the river area, the β ratio decreases to be 0.50, adequately explaining
the outflows of its girders. For the Kawahara Bridge, the β ratio becomes 2.92 as the greater tsunami
velocities nearby. For the Hamada Bridge, as the tsunami velocity (6.1m/s) is relatively close withwhat we assumed previously, the β ratio is not changed obviously.
Recalculation for Entire Areas
Based on the average velocities measured from videos, the authors recalculated the β ratios for total 12
bridge girders in the velocity measured areas (Rikuzentakata, Shinkitagami, Shizukawa and Otsuchi,
Wakabayashi is not included as no bridges are calculated in there). The calculation parameters andresults are shown in Table 7 and Fig. 15, respectively.
Compared with the summary results of former β ratios (velocity assumed as 6.0m/s) in different
areas (Fig. 16), we get to know the following phenomenon. For Rikuzentakata area, as the increasingof velocity (6.0m/s vary to be 7.0m/s), the β ratios have reduced entirely. The β ratio of girders for
Numatakosen Bridge (Rank A, Mark A of Fig. 15) reduced to be smaller than 1.0, reflecting outflow

1395

Numatakosen
Kawaharagawa
4.30
Kesen
Hamada
Avg.
3.47

=S/F

4
3

6
5
2.83

2.64

2.92
2.73

2
1.34
1 0.99 1.17
0Shizugawa3

Former Current

Rank A

Rank C0

Rank A

5

Shizugawa

Rank C

Rank A

D
0.91

0.96

0.86

Avg.
Otsuchi

ShinkitakamiC

Rank C

Rank A

Rank C

Rank A

Rank C

Shinchi

UtatsuKoizumi

4.34

4

= S/F

3.47

3

A,1.34

2

B
0.74

1
0

Rikuzentakata

OtsuchiFig. 15 Recalculated β ratios for entire area

Fig. 14 Recalculated β Ratios for Rikuzentakata

6

2.55
A, 0.99B
0.80

1Former Current

Avg.
Shinkitakami

4.64

4

2
1.06
0.78
0.50

Rikuzentakata

= S/F

5

Rank A

Rank C

1.17
Rank A

Rank C

Rank A

1.03

0.88

0.75
Rank C

Rank AF

E

D

C

Rank C

Rank A

0.90 G
0.96
a

0.93
Rank C

Rank A

Rank C

Rank A

Rank C

Fig. 16 Former β ratios for entire area

Table 7 Recalculated β Ratios for entire area
BridgeHamadagawa

1

PC-T

C

Rikuzen- Kawaharagawa
takata Numata-kosen

1PC-hollow

C

2

PC-T

A

Kesen
Shinkitakami

Shizugawa

Otsuchi

1 5 Steel plate

Avg.
β
β
v (6.0m/s) (avg. v)
[m/s]
S/F
S/F

7

2.64

1.94

4.30

3.16

1.34

0.99

A

0.99

0.73

Shiaikawa

1

Steel box

A

0.57

0.74

Shikitagami

1,2Steel truss

A

0.92

1.18

Hachiman

3

PC-I

C

4.88

5.22

Shiomi

3

PC-I

C

3.79

4.06

M izujirigawa

3th

PC-I

A

0.59

0.63

1st

RC-I

A

0.52

0.56

3

RC-I

A

0.64

0.69

4th

Steel-H

A

1.36

1.45

M izujiri

3

Steel-H

A

0.61

0.65

Namiita

1

PC-T

C

0.88

0.91

Hachimangawa 2

5.3

5.8

5.9

1396

5

Concrete girder
Steel girder
Average

4

β=S/F

Location

DamageSpan Span type
Rank

6

3

2

1.81

1

0

0.90
Concrete

Steel

Rank A

Concrete

Steel

Rank C

Fig. 17 β Ratios for entire area

condition more accurately. For other three areas, as the slight variation of tsunami velocities, the βratios do not have significant change.
As a result, after recalculations by using the detailed tsunami velocities for four velocity measured
areas, the β ratios do not have great variations. Differences of β ratios between Rank C and Rank A
bridges are also obvious. Trend of β ratios can fit the damage conditions well.
However, after recalculations, there are still some β ratios of Rank A bridges greater than 1.0(Mark B, Mark C, Fig. 15) while some of Rank C bridges are smaller than 1.0 (Mark D, Fig. 15).
Further, for the areas without measurement of velocities, some β ratios also can not coincide with theiroutflow conditions (Mark E, F, G and Section a, Fig. 16). A series of numerical analysis for getting
more detailed and precise velocities will be conducted later. After that, more precise β ratios will beobtained and the evaluations will be continued. Besides that, the average β of Rank A and C bridges
after modifications is plotted in Fig. 17. Compared to the average β before modification (Fig. 11), it isfound that the β of Rank C become smaller which is 1.81.
CONCLUSIONS
Based on investigation results, damage analysis to structures in Rikuzentakata region has been
conducted. Further, tsunami velocity is also evaluated. Thus, following conclusions can be drawn:
In Rikuzentakata, 70% of RC buildings in the survey area suffered non-structural damage, whichsuggests the great resistance; while all timber buildings were washed away; around 40% bridges
flowed out.
Difference of β ratios between Rank C and Rank A bridges for both Rikuzentakata and entire
Tohoku area are obvious. β ratios can coincide with damage conditions. β ratio is an effective indicator
to judge outflows of superstructures.
The average tsunami velocity for Rikuzentakata is 7.0m/s, greater than 6.0m/s of entire Tohoku
area.
REFERENCES
Institute of Industrial Science, University of Tokyo. (2011). “Interim report for criteria of buildings intsunami affecting area,” 2.1-2.12.
Imai, K., Matsutomi, H. (2006). “Hydroulic characteristics on tsunami inundation in a costal vegetatedarea,” J. JSCE B, Vol.62 No.3, 258-269.
Japan Institute of Construction Engineering. (2011). “Inundation Map for Rikuzentakata.”(http://www.jice.or.jp/sinsai/files/001393-004.pdf)
Japan Road Association. (2002). “Specifications for Highway Bridges Part I Common.” 47-52.
Matsutomi, H. (1998). “Tsunami current velocity on land and its simple estimation method,”
Proceeding of Coastal Engineering, JSCE, 361-365.
Rabbat, B.G., Russel, H.G. (1985). “Friction coefficient of steel on concrete or grout,” Journal of
Structural Engineering, ASCE, Vol.111, No.3, 505-515.
The 2011 Tohoku Earthquake Tsunami Joint Survey Group. (2011). “Field survey result,”(http://www.coastal.jp/ttjt/index.php?)
Taro, A. (2012). “Tsunami damage induced by Tohoku Earthquake,” Concrete Journal, Vol.50 23-29

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