Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, JapanDAMAGE OF RUBBER BEARINGSAND DAMBERS OF BRIDGESIN 2011 GREAT EAST JAPAN EARTHQUAKE
Yoshikazu TAKAHASHI1
1

Associate Professor, Disaster Prevention Research Institute, Kyoto University,Kyoto, Japan, yos@catfish.dpri.kyoto-u.ac.jp

ABSTRACT: In the 2011 Great East Japan Earthquake, many structures were heavily
damaged by Tsunami, but most structures designd by post-1990 code were not damagedby ground motion. However in some bridges designed by post-1995 code, rubberbearings and dampers were severely damaged. In this earthquake, cracks of rubber
bearings were observed in the wide region in the east part of Japan, and in Sendai area
the rupture of bearings were occurred in two highway viaducts. The paper summarizes
damage of rubber bearings and dampers of bridges.
Key Words: Rubber bearing, Damper, Bridges, Great East Japan earthquake

INTRODUCTION
The 2011 off the Pacific coast of Tohoku Earthquake with moment magnitude of 9.0 occurred at 14:46(local time in Japan) on March 11, 2011 along the Japan Trough in the Pacific. It was the sixth largest
earthquake ever recorded in the world. The fault zone extended 450 km and 200 km in the north-south
and west-east directions, respectively. Extensive damage occurred in the wide region in the east part ofJapan.
The author surveyed Miyagi Pref. and Iwate Pref. between March 13-16 to collect damage ofbridges induced by the ground motion, and was dispatched by Japan Society of Civil Engineers forfield damage investigation to bridges between March 29-April 3, 2011. In addition to theseinvestigations, damage investigations ,including Ibaragi Pref. and Kanagawa Pref., were conducted
several times. This paper presents damage of rubber bearings and dampers of bridges.

GROUND MOTION RECORDED AROUND BRIDGES
A number of strong motion accelerations were recorded by Japan Meteorological Agency (JMA), theNational Institute of Earth Science and Disaster Prevention (NIED), Ministry of Land, Infrastructure,
Transport and Tourism (MLIT). And NEXCO also has a network of seismometer for traffic control.
Rank 7 of JMA seismic intencity is recorded at Tsukidate, Miyagi-Pref. The ground motion continued
over 300 seconds, and the peak ground acceleration of 2765 gal was recorded.

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Fig. 1 Location of bridges shown in this article (red star) on aftershock distribution map

Fig. 2 Location of bridges and seismograph station1334

K-net Sendai
NEXCO SendaiHigashi
NEXCO SendaiPortKita
NEXCO RifuShiogama
NEXCO ShirakashiDai

K-net Sendai
NEXCO SendaiHigashi
NEXCO SendaiPortKita
NEXCO RifuShiogama
NEXCO ShirakashiDai

10000

Sa (gal) [h=0.05]

Sa (gal) [h=0.05]

10000

1000

1000

100

100

NS dir.

EW dir.

10100.1

1Period (sec)50.1

1Period (sec)5(a) Sendai Area
K-net Hitachi
MLIT Hitachi
NEXCO Hitachi Kita

K-net Hitachi
MLIT Hitachi
NEXCO Hitachi Kita

10000

Sa (gal) [h=0.05]

Sa (gal) [h=0.05]

10000

1000

1000

100

100

NS dir.

EW dir.

10100.1

1
Period (sec)50.1

1Period (sec)5(b) Hitachi Area
K-net NakaMinato
NEXCO MitoMinami

K-net NakaMinato
NEXCO MitoMinami

10000

Sa (gal) [h=0.05]

Sa (gal) [h=0.05]

10000

1000

100

1000

100

NS dir.

EW dir.

100.1

1
Period (sec)5100.1

1
Period (sec)5(c) Mito Area

Fig. 3 Response Spectra with JRA Design Spectra (L2-Type II)
Fig. 2 shows the distribution of seismograph stations around the bridges and the response spectra
are shown in Fig. 3. In Sendai area, K-net Sendai and NEXCO Sendai Higashi are similar to the
Design Spectra of Level II – Type II (Soil Type I), but the other ground motion are smaller than the
Design Spectra especially in 0.5-5 second.
JRA SEISMIC DESIGN SPECIFICATIONS REVISED AFTER 1995
The Kobe Earthquake (Hyogo-ken Nanbu Earthquake) of January 17, 1995, caused destructive
damage to highway bridges, including collapse of superstructures, occurred at 25 sites. Based on thelessons learned from the earthquake, the Japan Road Association’s (JRA) Specifications for Highway

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Bridges, Part V: Seismic Design were significantly revised in 1996. The intensive earthquake motion
with a short distance from the inland earthquakes with Magnitude 7 class has been considered in thedesign. As the design philosophy for large earthquakes, the JRA code does not allow critical damage
for standard bridges and allow limited damage for important bridges. The 1990 JRA code required thatRC piers be designed by ductility design method, but the 1996 JRA code expanded the scope ofapplicability of the ductility design method to include not only RC piers but steel piers and otherstructural elements that are seriously affected by earthquake such as foundations, unseating prevention
systems and bearings.

SUMMARY OF URGENT SAFETY INSPECTIONS OF BRIDGES
After March 11, 2011, MLIT conducted urgent safety inspections of 1,504 bridges of 11 National
Route in Iwate, Miyagi and Fukushima Prefectures in which strong seismic intensity of stronger thanrank of 6 lower was recorded. 1,350 bridges were located in area of seismic intensity of stronger than
the rank of 5 upper and 815 bridges were suffered damage (Maeda et al. 2011). In this earthquake, nobridges were severely damages induced by ground motions but 140 bridges were affected by Tsunami
and girders of 5 bridges on Route 45 were washed away by Tsunami.
The major damage of bridges is subsidence of backfill soil of abutments (364 bridges) andbearings (80 bridges) and expansion joints (67 bridges). The main failures of bearings were excessive
movement and breakage of side block of steel bearings.

BRIDGES WITH DAMAGED RUBBER BEARINGS
Rubber bearings including elastomeric bearings and seismic isolators are installed to improve theseismic performance of bridges. In the past earthquakes, there was no report of significant damage ofrubber bearings and their high deformation performance protected the function of bridges even
abutments moved. However the Great East Japan Earthquake disproved a widespread myth of therubber bearing’s safety.
Tobu Viaduct (Sendai Tobu Toll Road)
Tobu viaduct (Photo 1) is located between Sendai Higashi IC and Sendai Port Kita IC in Sendai Tobu
Tall Road. Photo 2 shows the ruptured elastomeric bearings. This rupture caused that the deck offset in
the transverse direction and settled aside the ruptured bearings. Rubber layers detached from steel
plates as well as rupture inside rubber layers. Fig. 4 shows the location of rupture of elastomericbearings, and the damage is concentrated at the edge of the girders (on Piers 52 and 56). At Piers 52and 56, the superstructure changes from steel I-girders to steel box girder and the substructure alsochanges from single-column piers to two-column piers. It is pointed out that one of the possible
reasons for the rupture of elastomeric bearings is that the interaction between adjacent bridges withdifferent natural periods was not properly considered in design of elastomeric bearings.	  	 Photo 1 Tobu Viaduct (Left: Pier 52, Right: Pier 56)

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Courtesy of NEXCO East 	 Photo 2 Rupture of elastomeric bearings of Tobu Viaduct
6径間連続桁

4径間連続桁

2径間連続桁S1

S1S2S2S3S3S4S4S5S5S6S6S7S7S8S84径間連続桁

4径間連続桁ゴム支承破断Fig. 4 Location of ruptured elastomeric bearings of Tobu Viaduct

Rifu Viaduct (Sendai Hokubu Toll Road)
Rifu viaduct is located between Rifu JCT and Rifu Shirakashi IC in Sendai Hokubu Toll Road.
Several elastomeric bearings ruptured in the transverse direction as shown in Photo 3. Fortunately thisrupture didn’t cause that the deck settled aside the ruptured bearings. Fig. 5 shows the location ofrupture of elastomeric bearings. The urgent safety inspection after March 11 reported that 3 bearings
ruptured. After the aftershock of Magnitude 7.4 on April 7, the urgent inspection was conducted again
and it was found that another 8 bearings ruptured. Since the section area of the elastomeric bearings
was larger than the conventional steel bearings, they could support the girders after their breakage but
couldn’t provide the function of resist lateral force. The big aftershock gave us another importantlesson how to provide not only the vertical support but also the lateral resistance in the restoration
process.

Courtesy of NEXCO East

Photo 3 Rifu Viaduct and rupture of elastomeric bearings

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Photo 4 Various crack patterns of damaged elastomeric bearings of Rifu Viaduct
5径間連続桁S1

4径間連続桁

4径間連続桁S1S1

4径間連続桁ゴム支承破断S1S2Fig. 5 Rupture of elastomeric bearings of Rifu Viaduct

Shin Nakagawa Bridge (Higashi Mito Toll Road)
Shin Nakagawa Bridge (Fig. 6) is the cable-stayed bridge located at Mito City in Ibaragi Prefecture.
The steel box girder is supported by one tower and 5 piers. The bridge was completed in 1999. The 4
elastomeric bearings were installed on the piers and the bearings on 3 piers were ruptured in thelongitudinal direction (Photo 5). The bearings deformed about 45 cm and hit the prevention devices ofexcessive movement.

Fig. 6 Shin Nakagawa Bridge and location of ruptured elastomeric bearings

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Photo 5 Ruptured elastomeric bearings of Shin Nakagawa Bridge

Asahi Viaduct (Hitachi By-pass of Route 6)
Asahi Viaduct (Photo 6) is located at Hitachi City in Ibaragi Prefecture. The viaduct consists of 4-span
and 7-span continuous PC box girders. The bridge was completed in 2008. The 2 and 3 lead rubber
bearings were installed on the piers and the abutments, respectively, and one bearing on the abutment
was cracked in the earthquake (Photo 7). Since the bridge is located along the coastline, the bearings
were coated by rubber for prevention of corrosion. But the side stoppers of the bearings bite into therubber coat and prevent the deformation of the bearings.

Photo 6 Asahi Viaduct	 	 Photo 7 Damage of lead rubber bearings of Asahi Viaduct1339

Kinko JCT Viaduct (Kanagawa Route 1 Yokohane Line, Metropolitan Expressway)
Kinko JCT (Photo 8) is located at Yokohama City in Kanagawa Prefecture. The superstructure issimple steel I girder and supported by rubber pad type bearings. The side blocks were damaged andone bearing moved away from the original position.

Courtesy of Metropolitan Expressway

Photo 8 Kinko JCT Viaduct and damage of rubber pad

BRIDGES WITH DAMAGED DAMPERS
Dampers were installed in many bridges in Sendai area. There is no report that damper itself wasdamaged by ground motion. But the attachments and the anchors of some dampers were damaged.
These dampers were installed in the seismic retrofit program but were not properly considered indesign of the attachments. According to the damage, the strong motion must input into these bridges.
Since no measurement systems were installed in almost all bridges, it is difficult to evaluate the effectof the dampers on the seismic response of bridges.

Photo 9 Nakanose bridge and damage of anchors of dampers

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slightly buckled

Photo 10 Damage of attachments of dampers in bridges

IMPORTANT ISSUES RELATED DAMAGE OF RUBBER BEARINGS
Since a sectional area of a rubber bearing is larger than that of a conventional steel bearing, verticalgap of a girder does not occur immediately after the crack or the rupture of bearings, ex. Rifu Viaduct.
This is an advantage for quick recovery of transportation. On the other hand, this characteristic brings
our trouble to detect the damage of bearings in urgent safety inspections of girders. Somemeasurement systems are needed to detect the rupture of bearings.
To evaluate the seismic response of bearings, the information of the relative deformation is needed.
However since there were no measurement system in almost all bridges, it is very difficult to know theseismic behavior without any estimation. Recently the rubber bearings are designed to move not onlyin the longitudinal direction but also in the transverse direction. In these cases, the sliding evidence ofbearings cannot be obtained for the estimation of the maximum deformation. Some measurement
systems are needed to record at least the maximum deformation and the direction in these bearings.
CONCLUSIONSIn 2011 Great East Japan Earthquake, most structures designd by post-1990 code were not damagedby ground motion. However in some bridges designed by post-1995 code, rubber bearings anddampers were severely damaged. This paper summarizes damage of rubber bearings and dampers ofbridges and the characteristics of ground motion recorded around the bridges. Although more throughcollection of damage information as well as careful analyses is required, the following conclusions
may be tentatively deduced based on the findings presented herein:
1) Recorded ground motion continued over 300 seconds, and the peak ground acceleration is verylarge. However in most records the response acceleration around 0.5 – 2.0 second was less thanthe design spectra. Only K-net Sendai and NEXCO Sendai Higashi IC shows the closecharacteristics to the Level II (Soil Type I) ground motion.
2) Cracks of rubber bearings were observed in the wide region in the east part of Japan, and in Sendai
area the rupture of bearings were occurred in two highway viaducts. The damage was concentrated
near the edge of girders.
3) In some bridges, the attachments of dampers were damaged. Although there are many restrictions,especially the space of the attachments, it is very important to design properly to ensure thedamping performance.
4) Lack of measurement system for bearings’ response brings difficulties to estimate the damageprocess. In order to recover the trust of the performance of bearings and dampers, it is needed todevelop new measurement systems of devices1341

ACKNOWLEDGMENTS
The author expresses their sincere appreciation for a number of organizations and persons for theirkind support and cooperation for the field damage investigation. Special appreciation is extended toMr. Hirose of NEXCO East and Mr. Namikawa of Metropolitan Expressway.

REFERENCES
Kawashima, K. (2000). “Seismic design and retrofit of bridges”, Key note presentation, 12th World
Conference on Earthquake Engineering, pp. 1-20, Paper No. 1818, 2000.
Japan Road Association (1997). “Specifications for highway bridges, Part V Seismic design.” Maruzen,Japan.
Maeda, T. and Koyamada, K. (2011). “Damage of Bridges in 2001 Great East Japan Earthquake. (inJapanese)” Proc. of 29th Japan Road Congress, Paper No. 2009, 2011.

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