Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, JapanEVALUATION OF STRONG GROUND MOTIONS
OF THE 2011 GREAT EAST JAPAN EARTHQUAKEBASED ON NONLINEAR RESPONSE
OF STANDARD BRIDGES
Hiroshi MATSUZAKI1 and Kazuhiko KAWASHIMA2
1

Assistant Professor, Department of Civil Engineering, Tokyo Institute of Technology,
Tokyo, Japan, matsuzaki.h.aa@m.titech.ac.jp
2
Professor, ditto, kawashima.k.ae@m.titech.ac.jp

ABSTRACT: Intensities of ground motions recorded during the 2011 Great East Japan earthquake isevaluated based on nonlinear seismic response of three bridges. It is shown that response under JMA
Furukawa ground motion develops the largest response among the ground motions recoded during the2011 Great East Japan earthquake, however it is smaller than the response under JR Takatori groundmotion recorded during the 1995 Kobe earthquake. It is also noted that high PGA ground motions suchas K-net Tsukidate ground motions do not produce large response of the bridges.

Key Words: Intensity, Strong Ground Motions, Bridges, Nonlinear Response

INTRODUCTION

Response acceleration(m/s2)

Ground-motion-induced damage was limited to the bridges which were designed in accordance withthe post-1990 design codes (JSCE 2011, Kawashima 2012). It is considered that the intensity ofground motions during the 2011 Great East Japan earthquake was smaller than the Type I and II design
ground motions in the post-1990 design codes as shown in Fig. 1. The Type I and II design ground25

Ground I
Ground II Type I
Ground III
Ground I
Ground II Type II
Ground III

20
15
10
5
0
0

1

2

3

4

Natural period (s)Fig. 1 Type I and II design ground motions

1375

Acceleration (m/s2)

10
0
–10
10
0
–10
20
10
0
–10
30
20
10
0
–10
–20
–30
85

NS
(a) JMA Furukawa
NS(b) K-net Furukawa
NS(c) K-net Sendai

NS

90

95

100

105

Time (s)(d) K-net Tsukidate

30
20
10
0
0

140

NS
EW
UD
1

2

3

4

Natural period (s)(a) JMA Furukawa

30
20
10
0
0

NS
EW
UD
1

2

3

4

Natural period (s)(b) K-net Furukawa

30
20
10
0
0

2

3

100
80
60
40
20

NS
EW
UD
1

NS
EW
UD

120
Response acceleration (m/s2)

Response acceleration (m/s2)

Fig. 2 Ground accelerations recorded during the 2011 Great East Japan earthquake

0
0

4

1

2

3

4

Natural period (s)Natural period (s)(c) K-net Sendai(d) K-net Tsukidate

Fig. 3 Response acceleration spectra of ground motions during the 2011 Great East Japan earthquake
motions were set so that they represent ground motions which possibly developed at Tokyo during the1923 Great Kanto earthquake and the ground motions recorded during the 1995 Kobe earthquake (JRA1376

Acceleration (m/s2)

10
0
–10
10
0
–10

NS
(a) JMA Kobe
NS(b) JR Takatori

10
0
–10
0

NS

5

10

15

20

30
20
10
0
0

100

NS
EW
UD
1

2

3

Response acceleration (m/s2)

Response acceleration (m/s2)

Time (s)(c) KiK-net Ichinoseki-nishi
Fig. 4 Ground accelerations recorded during the 1995 Kobe earthquake
and the 2008 Iwate-Miyagi earthquake

4

Natural period (s)(a) JMA Kobe

30
20
10
0
0

NS
EW
UD
1

2

3

80
60
40
20
0
0

4

Natural period (s)(b) JR Takatori

NS
EW
UD

1

2

3

4

Natural period (s)(c) KiK-net Ichinoseki-nishi
Fig. 5 Response acceleration spectra of ground motions recorded during the 1995 Kobe earthquake
and the 2008 Iwate-Miyagi earthquake
1996 and 2002, Kawashima 2000).
Figs. 2 and 3 shows some typical ground accelerations recorded at K-net and JMA sites during
the 2011 Great East Japan earthquake and their acceleration response spectra. Though duration wasover 300s, only the accelerations for 20s including the peak are shown here. It should be noted herethat since only few K-net and JMA sites were resting on soft soil sites with majority sites being on stiffsites, direct comparison with the design ground motions cannot be meaningful. At the stiff sites, someground accelerations had very high response accelerations at short period range (less than 0.4s), butthey had response values less than 10m/s2 at period over 1s.
For examples, the ground acceleration at K-net Tsukidate (refer to Fig. 2) had a PGA of 27 m/s2
leading to a 129m/s2 response acceleration at 0.24s. JMA intensity was 7 in this city. However almost
no structural damage occurred in engineering structures here. This clearly shows that high PGA due tohigh frequency spike is not absolutely important for structural design for bridges. From this sense, theground motions recorded during the Great East Japan earthquake was not destructive to engineering
structures.
However it should be noted that at soft soil sites such as Osaki City (JMA Furukawa and K-net
Furukawa sites), response acceleration was 22m/s2 at 1.2s and 8-16m/s2 at 0.8-1.2s. Similarly the1377

Table 1 Ground motions
Earthquakes

Ground motions

2011 Great East Japan earthquake

1995 Kobe earthquake
2008 Iwate-Miyagi earthquake

JMA Furukawa
K-net Furukawa
K-net Sendai
K-net Tsukidate
JMA Kobe
JR Takatori
KiK-net Ichinoseki-nishi

PGA(m/s2)
5.68
5.86
18.0
29.3
8.91
7.84
40.2

PGV
(m/s)
0.84
0.91
0.83
1.11
1.05
1.65
0.98

PGD
(m)
0.25
0.27
0.25
0.16
0.30
0.57
0.31

response acceleration was 27m/s2 at 0.6s at K-net Sendai. Thus it is considered that response
accelerations were quite high at the sites where soils were weak.
This paper tries to evaluate the intensity of ground motions during the 2011 Great East Japan
earthquake based on seismic responses of several bridges in comparison with response of the samebridges under ground accelerations during the 1995 Kobe earthquake (MJMA7.3, MW6.9) and 2008
Iwate-Miyagi earthquake (MJMA7.2, MW6.9). Ground accelerations at JMA Kobe and JR Takatori
during the 1995 Kobe earthquake and KiK-net Ichinoseki-nishi during the 2008 Iwate-Miyagi
earthquake (refer to Figs. 4 and 5) are used in this study for this purpose. JMA Kobe and JR Takatori
ground accelerations are widely used for dynamic response analysis in design of bridges after the 1995
Kobe earthquake. Table 1 summarizes the PGA, PGV and PGD for seven ground motions. Ground
velocities and displacements were computed in the frequency domain with a high pass filter of
1/10Hz.

TARGET BRIDGESFor evaluating the intensity of ground motions among the three earthquakes, response of three target
bridges were compared. Though it is preferable to compare responses of various types of bridges, only
three span continuous plate girder bridges supported by four reinforced concrete columns and fiveelastomeric bearings per column are considered as shown in Fig. 6. The bridges supported by 10 m, 15
m and 20 m tall columns are called A-bridge, B-bridge and C-bridge hereinafter. The bridges were in
the important bridge category. Basic dimensions of the three bridges were designed based on thedesign specifications of highway bridges (JRA 2002). Type-II ground condition (moderate soil) was
assumed here. It should be noted however that only inelastic static analysis was conducted for
deciding dimensions. In real design, linear and nonlinear dynamic response analyses are conducted,
but they were not conducted for three target bridges here.
Based on the inelastic static analysis, a part of superstructure supported by a column is analyzed
independently with other sections, and this bridge column must satisfy the following requirement.
k hcW  Pa

(1)

where Pa is lateral capacity of a column, W is tributary weight of a superstructure-column system, andk hc is an equivalent seismic coefficient as
k hc  c z c s k hc 0  0.4c z(2)cs  1 / 2  a  1

(3)

where

1378

3×40m=120m
10m

9m

10m
P2

P1

9m
P3

P4

(a) A-bridge
3×40m=120m
15m

14m

P2

P1

14m

15m
P3

P4

(b) B-bridge
3×40m=120m
20m

19m

19m

20m
P2

P1

P3

P4

(c) C-bridge
Fig. 6 Target bridges
Table 2 Fundamental natural periods of the target bridges
A-bridge
1.14 s1.16 s8

Lateral force (MN)

Lateral force (MN)

Longitudinal direction
Transverse direction

6
4

A–bridge
B–bridge
C–bridge

2
0
0

200

400

600

800

B-bridge
1.22 s1.23 sC-bridge
1.25 s1.29 s8
6
4

A–bridge
B–bridge
C–bridge

2
0
0

200

400

600

Lateral displacement (mm)Lateral displacement (mm)(a) Longitudinal direction(b) Transverse direction

800

Fig. 7 Lateral force vs. lateral displacement skelton
where k hc0 is an elastic lateral seismic coefficient depending on zone, ground condition and thenatural period, cs is structural response modification factor,  a is design displacement ductility
factor and c z is zoning factor (1.0, 0.85 and 0.7 depending on zones).
Several iterations are required in the inelastic static analysis. Table 2 shows the fundamental
natural periods of the three bridges thus designed. Since the flexibility of elastomeric bearings
predominantly controls the fundamental natural period of the three bridges, the fundamental natural
period is close in the three bridges. This is insufficient to evaluate the intensity of ground accelerations,but as a preliminary evaluation, the following analysis was conducted.
The equivalent seismic coefficient k hc0 of the three bridges become 1.75 in both thelongitudinal and transverse directions. On the other hand, a lateral force vs. lateral displacement
skelton was evaluated based on a fiber element analysis as shown in Fig. 7. Thus the column design1379

Table 3 Determination of khc
A-bridgeLGTR
khc0
uy (mm)uu (mm)
μa
cs
khc

30.8
401
9.0
0.24
0.42

35.5
248
5.0
0.33
0.58

B-bridge
LG
TR
1.75
41.5
50.5
604
530
10.0
7.3
0.23
0.27
0.40
0.47

C-bridge
LG
TR
71.4
728
7.1
0.27
0.48

84.6
605
5.1
0.33
0.58
4.75m

4.25m

(a) A-bridge(b) B-bridge

4m

3.5m

2.5m

3.75m

(c) C-bridge

Fig. 8 Cross section of bridge columns
ductility factor  a was determined asa  1 

uu  u y

 uy

(4)

where u y and uu are the yield and ultimate displacements, and  is a safety factor (1.5 forimportant bridges and 1.2 for less important bridges). Thus,  a , cs and k hc are evaluated as shownin Table 3. It is noted that k hc is in the range of 0.4-0.58 depending on bridges and directions.
Fig. 8 shows the dimensions of columns of three target bridges. Width and depth of the column
are 3.75m  2.5m, 4.25m  3.5m and 4.75m  4m for A-, B- and C-bridges, respectively. 29, 32 and35mm deformed longitudinal bars are set in double in the longitudinal direction, while 22mm
deformed tie bars are set at 150mm interval. Cross bars with the same diameters and interval are set
inside the core concrete. 135 degree bent hocks are used at both ends of the ties and cross bars.
Pile foundations were designed so that the following requirement is satisfied to mitigate inelastic
deformation in piles.
k f  (1  c p )khc

(5)

in which kf is seismic coefficient for a pile foundation, and c p is an overstrength factor ( c p = 0.1).
Elastomeric bearings were designed so that the shear deformation of rubber  B is within thefollowing limit B  2 .5

(6)

uB
t e

(7)

where

B 

1380

Table 4 Shear strain of elastomeric bearings in static analysiskhc
uB (mm)B (%)

A-bridge
LG
TR
0.42
0.58
112
153
116
160

B-bridge
LG
TR
0.40
0.47
105
124
110
130
uB 

C-bridge
LG
TR
0.48
0.58
126
152
132
158

k hcWUKB(8)

in which u B is lateral displacement of an elastomeric bearing, te is the total thickness of rubber
layers, WU is a tributary weight of a superstructure, and K B is lateral stiffness of an elastomericbearing.
For simplicity of design, it was assumed here that five elastomeric bearings with the same size,
thickness and stiffness are used per column in the three bridges. The stiffness of five elastomericbearings was 2.36×104kN/m and 7.86×106kN/m in the lateral and vertical directions, respectively. As
mentioned before, this assumption led to the close natural periods in the three bridges. Table 4summarizes shear strain  B based on the inelastic static analysis. The size of elastomeric bearings isdetermined based on static and dynamic response analyses in a real design, however this process waseliminated in this study for simplicity as mentioned before. Thus the real response in the dynamic
response analysis under recorded ground accelerations are much larger than  B shown in Table 4 aswill be presented later.

ANALYTICAL IDEALIZATION
Three bridges were idealized by a three dimensional discrete model in dynamic response analysis. The
plastic hinge zone of columns was idealized using fiber elements. Elastomeric bearings and thesoil-structure interaction effect were idealized using a set of linear springs. Skelton curve andunloading & reloading hystereses of stress vs. strain relation of confined core concrete was assumed
based on Hoshikuma et al (1997) and Sakai and Kawashima (2006). Modified Menegotto-Pinto model(1973) was used to idealize the stress vs. strain hystereses of longitudinal bars.
In the dynamic response analysis, Rayleigh damping was used assuming 2 %, 4% and 20 % for
structural components, elastomeric bearings and soils, respectively.
Dynamic response analysis was conducted by imposing the three directional components of theground motions shown in Figs. 2 and 4. NS, EW and UD components were imposed in thelongitudinal, transverse and vertical directions of the bridges.

SEISMIC RESPONSE OF THREE BRIDGES
As will be described later, since the deck response is generally larger in the longitudinal direction than
the transverse direction, the deck response displacement of A-bridge in the longitudinal direction are
shown in Fig. 9 for comparison. The deck response displacement at P2 is focused for such a purpose.
The peak deck displacement is the largest under JR Takatori acceleration, and it reaches 0.66m which
is a quite large value for mitigating damage of expansion joints due to collisions between adjacent
decks. This response is also very tough for drivers for controlling automobiles. It is interesting tocompare this response to the response under JMA Furukawa acceleration. Both JR-Takatori and JMA
Furukawa ground accelerations have nearly 22m/s2 response accelerations at 1.2s which correspond to
the fundamental natural period of A-bridge. However the peak deck displacement is 0.46m under JMA

1381

0.4
0
–0.4
a) JMA Furukawa

Displacement (m)

0.4
0
–0.4

b) K-net Furukawa

0.4
0
–0.4

0.4
0.0
–0.4
85

c) K-net Sendai

90

0.4
0.0
–0.4
0.8
0.4
0.0
–0.4

0.4
0.0
–0.4
0

95

Time (s)d) K-net Tsukidate

100

105

15

20

e) JMA Kobef) JR Takatori

5

10Time (s)g) KiK-net Ichinoseki-nishi

Fig. 9 Deck response displacement at P2 of A-bridge in the longitudinal direction
Furukawa accelerations which is only 70% of the peak deck displacement under JR-Takatori
acceleration. Such a point cannot be known from only the comparison of response accelerations.
Obviously the peak deck displacement under K-net Tsukidate ground acceleration is only 0.13m
which is much smaller than the peak deck displacement under JMA Furukawa and K-net Furukawa
ground accelerations. The peak deck displacement under KiK-net Ichinoseki-nishi record is in acomparative level with the response under K-net Furukawa, K-net Sendai and JMA Kobe records.
Fig. 10 compares lateral force vs. lateral displacement hystereses at the top of P2 for the sevenground accelerations. The response ductility factor  r is defined as

r 

u max
uy

(9)

where u max and u y are the peak displacement and yield displacement at the top of column. The
response ductility factor  r is the largest (  r =5.1) under the JMA Furukawa record, but much

1382

Lateral force (MN)

10

10

10

10

5

5

5

5

0

0

0

0

–5

–5

–5

–5

–10
–0.1 0 0.1–10–0.1 0 0.1–10–0.1 0 0.1

–10
–0.2

0

0.2

Lateral force (MN)(a) JMA Furukawa

Lateral displacement (m)(b) K-net Furukawa (c) K-net Sendai(d) K-net Tsukidate

10

10

10

5

5

5

0

0

0

–5

–5

–5

–10

0

0.2

(e) JMA Kobe

–10
–0.2

0

0.2

–10
–0.1 0 0.1

0.4

Lateral displacement (m)(f) JR Takatori(g) KiK-net Ichinoseki-nishi

Fig. 10 Force vs. lateral displacement hystereses at the top of P2 column of A-bridge in thelongitudinal direction
Table 5 Response ductility factors of P2 column
Earthquakes
2011 Great East Japan
earthquake
1995 Kobe earthquake
2008 Iwate-Miyagi
earthquake

Ground motions
JMA Furukawa
K-net Furukawa
K-net Sendai
K-net Tsukidate
JMA Kobe
JR Takatori
KiK-net Ichinoseki-nishi

A-bridge
LG
TR
5.1
1.7
2.9
2.4
2.6
0.9
3.2
1.0
3.4
1.4
12.9
5.8

B-bridge
LG
TR
4.2
1.1
2.3
1.8
2.3
0.8
2.8
0.8
2.6
0.9
7.0
3.5

C-bridge
LG
TR
3.0
1.0
1.5
1.6
1.5
0.7
1.7
0.7
2.3
0.9
6.6
3.3

2.0

2.5

1.5

1.3

1.2

1.0

larger  r (=12.9) develops under JR Takatori ground accelerations. The column response ductility
factors have the similar trend with that of the peak deck displacement.
Table 5 summarizes the column response ductility factors of the three bridges subjected to sevenground accelerations. Note that response ductility factors  r by Eq. (9) are much smaller than thedesign ductility factor  a by Eq. (4) (refer to Table 3). In particular,  r in the transverse direction
is generally very small except  r evaluated for JR Takatori ground acceleration showing thatcolumns behave almost linearly. Column response ductility factor is the largest under JMA Furukawa
ground acceleration among the four ground accelerations recorded during the 2011 Great East Japan
earthquake, however the largest column response ductility factor under JMA Furukawa groundacceleration is smaller than the response ductility factor under JR Takatori ground acceleration
recorded during the 1995 Kobe earthquake. The similar results are obtained in B- and C-bridges.
Table 6 summarizes the peak shear strain of rubber layers in elastomeric bearings. Again in thiscase, shear strain computed by dynamic response analysis is much larger than the shear strain
evaluated by static analysis (refer to Table 4). As mentioned earlier, in a real design, the elastomeric1383

Table 6 Peak shear strain of elastomeric bearing on P2 column

Earthquakes

2011 Great East Japan
earthquake
1995 Kobe earthquake
2008 Iwate-Miyagi
earthquake

Ground motions
JMA Furukawa
K-net Furukawa
K-net Sendai
K-net Tsukidate
JMA Kobe
JR Takatori
KiK-net Ichinoseki-nishi

A-bridge
LG
TR
()
()
295
186
233
361
246
148
182
136
268
213
316
351

B-bridge
LG
TR
()
()
341
175
231
319
247
149
165
119
279
190
415
395

C-bridge
LG
TR
()
()
327
216
247
340
287
177
132
112
305
206
336
301

191

242

237

225

196

175

bearings have to be re-sized based on the computed shear deformation by dynamic response analysis,
however this process was eliminated in this study for simplicity. The general trend of the dependenceof ground accelerations is similar with the above results. JR Takatori accelerations results in the largest
shear strain in the elastomeric bearings followed by JMA Furukawa ground accelerations.

CONCLUSIONSIn this study, impacts of the ground motions recorded at soft soil sites during the 2011 Great East
Japan earthquake was evaluated in comparison with JMA Kobe and JR Takatori ground accelerations
which are widely used for dynamic response analysis in design. A ground acceleration recorded at
KiK-net Ichinoseki-nishi during the 2008 Iwate-Miyagi earthquake was also included in analysis forcomparison. Based on the results presented herein, the following conclusions may be deduced:
1) Most of ground accelerations recorded at K-net and JMA net were recorded at stiff sites. Thus
PGA and response accelerations at period shorter than 0.3s was extremely high, however it develops
only small response in the target bridges.
2) In particular, a ground acceleration at K-net Tsukidate had an extremely high PGA of 27m/s2
and high response acceleration of 129m/s2 at 0.24s, but it develops very small response in the target
bridges. This clearly explains the fact that the structural damage in Tsukidate during the 2011 Great
East Japan earthquake was minor though JMA intensity was 7.
3) On the other hand, a ground acceleration recorded at JMA Furukawa develops much larger
response in the target bridges than the ground acceleration recorded at Tsukidate. However the
response of the target bridges under JMA Furukawa ground acceleration is smaller than that under JR
Takatori acceleration recorded during the 1995 Kobe earthquake. Since the type II design response
spectra were determined based on the ground motions developed during the 1995 Kobe earthquake, it
is considered that the ground motions recorded at K-net and JMA-net during the 2011 Great East
Japan earthquake was smaller than the Type II design spectra. This is a major contribution to the factthat the bridges which were designed in accordance with the post-1990 design codes suffered almost
no damage during the 2011 Great East Japan earthquake.
4) A ground acceleration recorded at KiK-net Ichinoseki-nishi during the 2008 Iwate-Miyagi
earthquake develops similar or slightly smaller response in the target bridges than JMA Kobe groundacceleration recorded during the 1995 Kobe earthquake.
5) Since computed nonlinear response of the target bridges exhibits responses which are different
from expected response assessed based on only response spectra, it is important to evaluate intensityof ground motions based on nonlinear response of several target bridges with different structuralproperties. By identifying several bridges as target bridges among researchers, response comparison of1384

several target bridges can be a useful measure to evaluate the intensity of various ground motions.

ACKNOWLEDGMENTS
The authors would like to acknowledge the National Research Institute for Earth Science and Disaster
Prevention, and Japan Meteorological Agency for providing strong ground motion records used in thisstudy.

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