Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, JapanSEISMIC BEHAVIOR OF RETROFITTED BRIDGESDURING THE 2011 GREAT EAST JAPAN
EARTHQUAKE
Jun-ichi HOSHIKUMA1, Guangfeng ZHANG2 and Junichi SAKAI3
1

Chief Researcher, Center for Advanced Engineering Structural Assessment and Research,
Public Works Research Institute, Tsukuba, Japan, hosikuma@pwri.go.jp
2Researcher, Center for Advanced Engineering Structural Assessment and Research,
Public Works Research Institute, Tsukuba, Japan, tyou44@pwri.go.jp
3
Senior Researcher, Center for Advanced Engineering Structural Assessment and Research,
Public Works Research Institute, Tsukuba, Japan, sakai55@pwri.go.jp

ABSTRACT: In order to examine the effectiveness of the seismic retrofit for bridges
through the experience of the 2011 Great East Japan Earthquake, authors report theseismic behavior of some retrofitted bridges during the earthquake with comparison of
the damage of unretrofitted bridges, and summarize that the seismic retrofit for bridge
columns has been effective to prevent vulnerable failure in columns. It should be also
remarkable that the structural members attached with the additional shear keys or theunseating prevention devices were damaged in some retrofitted bridges.
Key Words: the 2011 Great East Japan earthquake, retrofitted bridge, shear keys,
unseating prevention devices

INTRODUCTION
The 2011 Great East Japan Earthquake occurred at 2:46 pm on March 11, 2011. The catastrophic
damage resulting from strong ground motion and huge tsunami was caused in Tohoku and Kanto
regions. More than 20,000 people were killed or missing and various infrastructures were damaged,
especially in the coastal area of Iwate, Miyagi, Fukushima and Ibaraki Prefectures. Many highway
bridges were damaged in these areas due to both large ground motion and tsunami inundation(Hoshikuma 2011). This paper focuses on the damage to retrofitted bridges due to the ground motion
effect. There were some retrofitted bridges with damage during the earthquake, while most of bridge
damage due to the ground motion effect was observed in the bridges designed with pre-1980
specifications. Seismic retrofit projects have been performed to bridges step-by-step since the 1995
Kobe earthquake, to prevent fatal damage of bridges due to the ground motion observed in the 1995
Kobe earthquake. Based on the lessons learned from the past earthquakes, bridge columns designedwith pre-1980 specifications have been retrofitted with high prioritization. It should be noted that such
retrofitted bridges were actually excited due to the 2011 Great East Japan earthquake.
This paper presents the seismic behavior of some retrofitted bridges during the earthquake withcomparison of the damage of unretrofitted bridges, so that examine the effectiveness of the seismic
retrofit for bridge columns with insufficient development length of the cut-off longitudinal1323

reinforcement bars at mid-height section. Remarkable damage of the structural members attached withthe additional shear keys or the unseating prevention devices in the retrofitted bridge is also introducedin this paper.

THE 2011 GREAT EAST JAPAN EARTHQUAKE AND GROUND MOTION
The main shock of this earthquake (Mw=9.0, focal depth=24km) occurred at 2:46 pm (JST) on March
11, 2011. Maximum seismic intensity was observed at Tsukidate, Kurihara city in Miyagi prefecture(Seismic intensity of JMA was 7) and large seismic intensities were observed in Tohoku and Kanto
areas. Fig. 1 shows acceleration ground motion waveforms and spectral response accelerations at
representative strong ground motion observation sites. The location of some bridges shown later in thispaper is also marked on Fig. 1.
It should be noted that 1) strong ground motion records with long duration were observed and 2)
there were multiple pulses in some ground motion records observed near epicenter. This is because
large fault areas collapsed continuously. It was observed at very large maximum response acceleration
at the range of short predominant period such as Tsukidate record. The maximum response
accelerations at the range of natural periods from 1.0 to 2.0 seconds, which relatively correlate withdamage of ordinary road bridges, were equal or slightly less than those of the 1995 Hyogo-ken Nambu
earthquake. Ground motions and maximum response accelerations at the coastal area of Tohoku region
were not so large. However, strong ground motions and large response accelerations were observed at
the sites where located slightly far from epicenter such as Fukushima, Tochigi and Ibaraki prefectures.
Moreover, aftershocks with the JMA magnitude of 7.0 or over were occurred three times within a
day and total of 89 aftershocks with the magnitude of 6.0 or over were occurred until August 3.

OVERVIEW OF DAMAGE IN BRIDGES
Damage of the highway bridges due to this earthquake can be categorized as effect of strong groundmotion, effect of tsunami inundation, and effect of soil liquefaction. It should be noted in thisearthquake that the intensive damage in highway bridges was mainly caused by tsunami inundation.
Superstructures in twelve bridges including service road for pedestrian on national highway route 45(main route along the Pacific coast of Tohoku Area) were washed away, which resulted in the trafficclose after the earthquake. About 91 highway bridges in total were washed away due to tsunami
inundation in Iwate, Miyagi, Fukushima, Ibaraki and Chiba prefectures. On the other hand, as long as
we have investigated, 105 bridges survived even though the superstructures of these bridges wereinundated with the tsunami. The backfill of abutment in some bridges were also washed out eventhough super- and substructures survived.
The ground motion effect to damage of bridges was less significant than the tsunami effect. One
bridge (Rokko Ohashi Bridge, an old steel girder bridge supported by steel pile-bent columns locatedin Ibaraki prefecture) was collapsed due to the ground motion of the earthquake. Although thecollapsed bridge was observed at the only Rokko Ohashi in the highway bridges, it was found in thebridge designed in accordance with pre-1980 design specifications that damage to RC columns at
section of cut-off of longitudinal rebars, damage to RC pier-wall with small amount of reinforcement,
damage to steel bearings and attachment of bearings, damage to bracing and steel members, andsubsidence of backfill soil of abutment. These damage modes have already observed in the pastearthquakes. However, rupture of elastometric rubber bearings were observed at the Sendai-Tohbu
viaduct designed based on Post-1995 design specifications.
After the Kobe Earthquake, the seismic retrofit project has been performed for existing bridges
columns designed in accordance with pre-1980 specifications with high priority, to prevent thecollapse of the bridge structure and unseating of the deck. Almost of retrofitted bridge columns were
not damaged due to the ground motion of the earthquake, which would exhibit the effectiveness of theseismic retrofit.

1324

Fig. 1 Acceleration Waveforms and Spectral Response Acceleration at Main Shock (NS comp.)

1325

Soil liquefaction was widely observed in particularly Tokyo Bay area. Although the effect of thesoil liquefaction on the bridge damage was minor, subsidence of backfill soil of abutment due to thesoil liquefaction effect was developed in some bridges. Deck-end gap was shortened resulting frommovement of substructure, which caused steel bearings damage and cracks in parapet wall.

Photo 1 Damage of Reinforced Concrete Columns at Cut-off Section ofLongitudinal Reinforcement

Photo 2 Damage of Steel Bearing Support

Photo 3 Damage of Pier Top

Photo 4 Residual Inclination of Substructure and Damage of Pile Cap for Caisson Foundation

1326

BRIDGE DAMAGE DUE TO GROUND MOTION
Damage of Unretrofitted Bridges Designed in Accordance with Pre-1980 Design Specifications
Intensive damage due to the ground motion was developed in many unretrofitted bridges designed inaccordance with pre-1980 design specifications. Almost of damage modes of those bridges have everbeen observed in the past earthquakes. Photos 1 to 3 show the damage to reinforced concrete piers,
steel bearing supports and the attachment of the bearing support to pier top or the superstructure,
respectively. Photo 4 shows the residual inclination of substructure due to the damage of the pile cap
for caisson foundation.

Photo 5 Comparison of Seismic Performance between Adjacent Two Bridges(Kanagasaki Ohashi Bridge and Esaki Ohashi Bridge)

Comparison of Seismic Performance of Bridge between Retrofitted and Unretrofitted
Based on the lessons learned from the 1995 Kobe Earthquake, the seismic retrofit project has been
performed for existing bridges columns designed in accordance with pre-1980 specifications with highpriority, to prevent the collapse of the bridge structure and unseating of the deck. During the 2011
Great East Japan Earthquake, many retrofitted bridges were given a shake due to the ground motion.
Photo 5 exemplifies the effectiveness of the seismic retrofit for bridge columns. The unretrofitted
bridge (Esaki Ohashi Bridge) shown in the right side of Photo 5 suffered from severe shear damage inconcrete columns. Esaki Ohashi Bridge is 9-span continuous concrete box girder bridge designed in1972 design specification. Near Esaki Ohashi Bridge (as close as 4,000m), there is the other bridge(Kanagasaki Ohashi Bridge) as shown in the left side of Photo 5, where this is three 3-span continuous
steel girders bridge designed in 1974 and the columns were retrofitted by concrete jacketing. No

1327

structural damage was observed in this retrofitted bridge. Comparison of the seismic performance withthese two bridges indicates that the seismic retrofit for bridge columns work effectively, although
structural type of these bridges are different and thus the natural period is not equivalent between two
bridges.
Photo 6 shows the other example of the comparison of the damage between seismic retrofitted
bridge and unretrofitted bridge. As seen in Photo 6, there are two adjacent river-crossing bridges.
Since one bridge (Nakagawa Bridge) is on the designate emergency route, bridge columns designedwith the pre-1980 specifications have already been retrofitted by reinforced concrete jacketing. The
other bridge (Kunita Ohashi Bridge) is on the local roadway and the bridge columns have not yet been
retrofitted at the earthquake. Although Kunita Ohashi Bridge suffered from the vulnerable damage andthus lost the serviceability for the bridge, Nakagawa Bridge did not suffer from the damage and kept
the serviceability soon after the earthquake. Seismic performance shown in these two bridges clearly
exhibits the effectiveness of the seismic retrofit.

Unretrofitted Bridge（3‐span Cont. + 3‐span Cont.）

Retrofitted Bridge（3‐span Cont. + 4‐span Cont.）

No Damage（Serviceable soon after EQ）

400m

Shear Crack in RC Column（Bridge Closed）

Damage to Movable Bearing

Photo 6 Comparison of Seismic Performance between Adjacent Two Bridges(Nakagawa Bridge and Kunita Ohashi Bridge)

Damage of Cap Beam in Retrofitted RC Column
There are a few remarkable damage examples in the retrofitted bridges. Photo 7 shows adjacent two
reinforced concrete columns in Kameda Ohashi Bridge. Each column supports 2-span continuous steel
box girder at the middle. The outbound column was designed with 1980 specifications and retrofitted
by reinforced concrete jacketing for strengthening the cut-off section without increasing the flexuralstrength of the column base. Furthermore, additional shear keys were anchored to cap beam tosupplement the strength of the existing steel bearings. Although no damage was found to the steel
bearings and shear keys, vertical cracks of nearly 10mm width were observed at the section of cap
beam as shown in Photo 7. The inbound column was designed with 1994 specifications basically and1328

some modifications were made based on the 1995 tentative specifications (published soon after 1995
Kobe Earthquake). In the inbound column, elastometric rubber bearings were deformed in thetransverse direction and the side stoppers were failed. Concrete of the cap beam edge portion attaching
the supplemental shear keys also spalled off (see in Photo 7) due to the transverse seismic force
induced by the inertia of the superstructure, while vertical crack observed in the cap beam of theoutbound column was not developed in the inbound cap beam.
Amount of tensile steel bar in the cap beam was different between two columns. Tensile
reinforcement ratio of the cap beam is 0.40% in the inbound column, while 0.24% in the outboundcolumn. The section of the cap beam has been designed predominantly by the live load rather than theseismic effect. Actually the design live load is different between two columns, because the design
specifications of the live load revised and larger live load was considered into the design of theinbound column. The difference of strength of the cap beam would affect the failure mode for the large
seismic lateral force.
Table 1 shows the analytical result of the strength capacity of some sections in two columns when
the transverse seismic force applies at the superstructure. The result of the push-over analysis indicatesthat the section of the cap beam shoulder (Section 3 in Table 1) in the outbound column is the first
failure section regardless the effect of the seismic retrofit, while the section of the column base is thefirst failure section so that the cap beam be protected in the inbound column. These results coincidewith actual behavior of the columns observed after the earthquake.

Photo 7 Comparison of Damage Mode between Adjacent Two Bridge Columns(Kameda Ohashi Bridge)1329

Table 1 Comparison of Strength in Columns of Kameda Ohashi Bridge
Outbound before retrofit

Outbound after Retrofit (current)

InboundPs1-1 = 6,440 kN
Ps2-1 = 6,117 kN
Ps3-1 = 5,100 kN
Ps4-1 = 10,040 kN
Ps3-1 < Ps2-1 < Ps1-1< Ps4-1

Ps1-2 = 6,850 kN
Ps3-2 = 5,100 kN
Ps4-2 = 10,040 kN
Ps5-2 = 11,110 kN
Ps3-2 < Ps1-2< Ps4-2< Ps5-2

Ps1-3 = 8,450 kN
Ps3-3 = 10,100 kN
Ps4-3 = 7,040 kN
Ps5-3 = 11,110 kN
Ps4-3 < Ps1-3< Ps3-3< Ps5-3

Ps1-1, Ps1-2, Ps1-3 : Flexural strength of the base section of the column (section 1)
Ps2-1 : Flexural strength of the cut-off section of the longitudinal reinforcement (section 2)
Ps3-1, Ps3-2, Ps3-3 : Flexural strength of the section of the cap beam shoulder (section 3)
Ps4-1, Ps4-2, Ps4-3: Shear strength of the shear key for the rubber bearing (section 4). This shear key was
designed based on earthquake with high probability of occurrence for the bridge service
life (level 1 earthquake ground motion)
Ps5-2, Ps5-3 : Shear strength of the shear key (section 5). This shear key was designed based on strong
earthquake with low probability of occurrence for the bridge service life (level 2
earthquake ground motion)

Damage of Steel Truss Attached with Cable Restrainer
Photo 8 shows the other example of the damage in the retrofitted bridge. Osaragi Ohashi Bridge is a
3-span continuous steel truss bridge and the cable restrainers are installed so as to prevent from
unseating of the superstructure in the event of unexpected failure of bearing supports during anearthquake. In this steel truss bridge, the cable restrainers were attached to the lower chord with steel
bracket and additional steel plate for strengthening of the section of attachment as shown in Photo 8.
Any bearing supports didn’t suffer from the damage due to the earthquake and there was no evidenceof the superstructure movement, which indicated that the cable restrainers didn’t work during theearthquake. However, the lower chord was slightly buckled at near the section of attachment for thecable restrainer. This damage was caused by the seismic force transmitted from the fix bearing support1330

(not from the cable restrainer). Significant change of the stiffness and strength at the section of theattachment may cause the buckling due to the cyclic loading.

Photo 8 Damage of the lower chord of truss bridge (Osaragi Ohashi Bridge)

IMPACT OF 2011 GREAT EAST JAPAN EARTHQUAKE ON SEISMIC DESIGN OF
HIGHWAY BRIDGESThe seismic performance of retrofitted highway bridges was very well except a few bridges describedabove. The retrofitted bridges were functional without any long-term traffic stops after the earthquake.
However, there are several important issues and lessons we should study and review for the latest
seismic design specifications for highway bridges. Followings are the selected issues.
Ground Motion
In the 2011 Great East Japan Earthquake, many strong ground motion records were recorded and theserecords clearly showed that this earthquake generated ground motions with multiple pulses and thus
the longer duration (more than 2 minutes) than other records observed in the past earthquakes. Similar
ground motions were reported in the 2010 Chile Earthquake with the moment magnitude Mw 8.8(Chen 2010a, Kawashima 2010b). Therefore, the subduction-type earthquake with Mw of nearly 9
may induce the ground motion with long duration.
In general, the long duration would affect the number of cyclic inelastic response of the bridge
system. Past experimental researches indicated that the loading pattern in the quasi-static cyclicloading test, particularly the number of cyclic loading affects the ductility capacity of flexural
reinforced concrete column. In order to accommodate such effect into the seismic design, Japanesedesign specifications have determined two ductility/shear capacity factors based on the types of theground motion, i.e. the subduction-type and the near-fault-type. Re-studies on the effect of the long
duration will be required based on the ground motion observed in the 2011 Great East Japan
Earthquake.
The long duration would also affect the soil liquefaction. Effect of the soil liquefaction on theseismic design of bridge foundation was introduced in the 1971 specifications in Japan based on thelessons learned from the 1964 Niigata Earthquake. Although there were no major liquefaction-induced
damages in bridges during the 2011 Great East Japan Earthquake, the long duration effect on thebridge performance built on the liquefiable sandy soil condition should be verified through both
geological and structural perspectives.
Since the ground motion effect propagated wide, bridge damage developed in wide area. Manyground motion records were also observed in wide area. It should be also important to study the
relation between the properties of the ground motion and damage of bridges.

1331

Validations of Effectiveness of Seismic Retrofit
Seismic retrofit have been performed step-by-step since 1995 Kobe earthquake. Based on the lessons
learned from the past earthquakes, bridge columns in the important highway network designed by
pre-1980 specifications have been retrofitted with high prioritization. Many seismic vulnerable bridges
in the important route such as National Highway Route 4, 6, 45 etc were retrofitted up to the date of
the earthquake, which resulted in quick recovery of the functional highway network after theearthquake. It should be, however, important review to investigate details of the new type of damage
in the retrofitted bridges described in this paper and evaluate the seismic behavior of the bridge during
the earthquake.

CONCLUSION REMARKSThis report summarized damage to highway bridge due to the 2011 Great East Japan Earthquake withfocus of the seismic performance of the retrofitted bridges. Based on the damage caused by theearthquake, more analytical and experimental researches should be required to clarify the mechanismof the damage. Investigation results also indicate that subsidence of the backfill soil in the abutment
has been remarkable with the improvement of seismic performance for bridge structures, thoughdetails are not reported in this paper. It would be important to ensure the seismic performance of bothbridge structures and embankment for highway.

ACKNOWLEDGMENTS
Damage investigation was supported by a number of organizations. Special appreciation is extended to
Iwate Pref., Ibaraki Pref., Chiba City, Kitakami City, Tohoku Regional Development Bureau, Kanto
Regional Development Bureau and Headquarter of MLIT.

REFERENCES
Chen G., Yen P. W., Buckle I., Allen T., Alzamora D., Ger J. and Arias J. G. (2010a): 2010 Chile
Earthquake Implication to the Seismic Design of Bridges, Proc. 26th US- Japan Bridge Engineering
Workshop, 2010.
Hoshikuma J. (2011): Damage of Highway Bridges Due to the Great East Japan Earthquake, Proc.
27th US- Japan Bridge Engineering Workshop, 2011.
Kawashima K., Unjoh S., Hoshikuma J. and Kosa K. (2010b): Damage Characteristic of Bridges due
to 2010 Chile Earthquake, Proc. 26th US- Japan Bridge Engineering Workshop, 2010.

1332