Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, JapanDAMAGE TO REINFORCED CONCRETE SCHOOL
BUILDINGS IN MIYAGI AFTER THE 2011 GREATEAST JAPAN EARTHQUAKE
Masaki MAEDA1, Hamood Ahmed AL-WASHALI2, Kanako TAKAHASHI3
and Kazuki SUZUKI4
1

Professor, Department of Architecture and Building Science, Tohoku University,
Sendai, Japan, maeda@archi.tohoku.ac.jp
2
Graduate student, Department of Architecture and Building Science, Tohoku University,
Sendai, Japan, hamood@sally.str.archi.tohoku.ac.jp
3
Graduate student, Department of Architecture and Building Science, Tohoku University,
Sendai, Japan, takahashi@sally.str.archi.tohoku.ac.jp
4
Graduate student, Department of Architecture and Building Science, Tohoku University,
Sendai, Japan, suzuki@sally.str.archi.tohoku.ac.jp

ABSTRACT: Typical damage observed by author’s field survey in Miyagi prefecture is
described. Generally, reinforced concrete structures performed well and effect of seismic
retrofit was found in mitigation of damage, although severe damage to some seismically
retrofitted buildings was noticed. Some buildings are selected for detailed investigation.
A good correlation was observed between calculated seismic capacity Is-index andobserved damage. However, major damage to non structural elements was commonly
observed. The reasons for damage and lessons to seismic design are discussed.
Key Words: Great East Japan earthquake, RC school buildings, damage survey, seismic
evaluation, seismic retrofit.

INTRODUCTION
This paper is to describe reconnaissance activities of AIJ, Architectural Institute of Japan, after the2011 East Japan Earthquake. Typical damages to reinforced concrete school buildings are outlined,
both by the ground motion and tsunami waves, based on the field observation data of about two
hundred school buildings in Miyagi region.
The school building committee and the reinforced concrete steering committee of AIJ jointly
organized a special task committee and working groups on the post-earthquake investigation anddamage evaluation of school buildings and educational facilities. The activity was also supported by
the facility division, the ministry of education, science, sport and technology (MEXT). The members
conducted the field survey from the middle April to the late June based on the request of the local
governments in charge of the facility administration.

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First, characteristics of strong motions records observed are introduced and compared withprevious earthquakes. Secondly, the damage level statistics of the investigated buildings in Miyagi
prefecture and its correlation with the Japanese seismic performance indices are presented. The
damage was rated into five levels which are; collapse, severe, moderate, minor, slight and no damage,
based on the “Post-earthquake damage evaluation standards of Japan” (JBDPA 2001a). The local
government and MEXT judged restoration procedure of repair or reconstruction based on theevaluated damage levels. Finally, typical damage observed is presented. Comments, lessons andrecommendations from the damage induced by the Great East Japan earthquake are discussed.

GROUND MOTION IN MIYAGI REGION
General Information of 2011 East Japan Earthquake
Figure 1 shows the location of Miyagi Pref. and epicenter of this earthquake. The 9.0-magnitude (MW)undersea earthquake occurred on 11 March 2011 at 14:46 JST (Japanese Standard Time )in the western
Pacific Ocean at a depth of about 24 km, with its epicenter about 72 km east of the Oshika Peninsulaof Miyagi, Japan(AIJ 2011).
Observed Strong Motion Records
Figure 2 shows the locations of strong ground motion observation stations. Strong motion records atover 30 stations in Miyagi Pref. from this earthquake were obtained by various organizations,
including the Japan Meteorological Agency (JMA), K-NET from National Research Institute for Earth
Science and Disaster Prevention (NIED), and Building Research Institute (BRI).

Iwate

Epicenter
38°6.2′N 142°51.6′E

MiyagiK-net observation s
JMA observation s

Fukushima
Tochigi

BRI observation s

IbarakiFig.1 Location of Miyagi Pref. andepicenter of the earthquake

Fig. 2 Locations of strong ground motion
observation stations in Miyagi Pref.

According to JMA, the earthquake may have ruptured the fault zone from Iwate to Ibaraki Pref.
with a length of 500 km and a width of 200 km, therefore both acceleration time histories have plural1121

peaks, and the duration of ground shaking is very long, about 180 sec. Due to long duration, soilliquefaction occurred at several locations from Tohoku district to Kanto district.
Table 1 shows the records of ground motion for intensities over 5.6 using JMA Seismic Intensity
Scale observation stations in Miyagi pref. Several records exceed 1000 gal in their peak groundaccelerations(PGA) and the maximum recorded acceleration was 2699 gal obtained at MYG004, N-S
direction.
Figure 3 shows 5%-damped acceleration response spectrum and comparison with past major
earthquakes.MYG004 has extremely high acceleration response, 11852gal, in the very short period(T<0.5sec). MYG013 and 4B9 has a response spectrum peak around 1sec, also the peak value of theiracceleration response is almost as same as JR Takatori at 1995 Kobe and Country Hospital at 1994
Northridge, which had severe damage.
Table 1. Records of ground motion at each observation stations in Miyagi pref.
Name of station
MYG004
MYG006
MYG007
MYG010
MYG011
MYG012
MYG013
MYG015
MYG017

direction
NS
EW
NS
EW
NS
EW
NS
EW
NS
EW
NS
EW
NS
EW
NS
EW
NS
EW

PGA（gal）
2699.11268.6
444.1
571.5
568.0
650.9
458.2
377.0
921.0
688.2
758.5
1969.11517.1
982.3
410.7
353.2
317.4
349.3

JMA Scale※
6.67
6.16
5.81
5.93
5.63
6.02
6.38
5.99
5.83

direction PGA（gal） PGV（kine） JMA Scale※
NS
359.5
54.6
8A3(Matsushima)
5.74
EW
336.9
70.1
NS
405.8
87.2
8A4(Wakuya)
6.02
EW
438.7
80.7
NS
389.6
55.6
8A5(Tome)
5.75
EW
433.9
52.7
NS
551.8
49.5
8A6(Kurihara)
5.70
EW
710.7
35.9
NS
379.1
28.0
4B8(Kesennuma)
5.80
EW
664.4
54.6
NS
549.6
78.0
4B9(Osaki)
6.21
EW
456.4
86.9
NS
409.9
53.9
E06(Sendai)
5.69
EW
317.9
54.2
NS
332.8
49.2
THU
5.60
EW
329.8
61.1
※JMA Scale＝Japan Meteorology Agency Secimic Intencity Scale
Name of station2011 East Japan MYG004

3000
5% damped Response Spectrum
Accellaration(cm/sec 2 )PGV（kine）
117.6
51.2
50.6
89.1
34.9
34.1
51.5
53.1
18.6
35.5
31.6
61.8
84.3
43.0
69.9
52.6
45.6
49.2

1994 Northridge
2011 East Japan MYG013

2500

2011 4B9
1995Kobe

2000
1500

2011 Chiristcurch

1000
500
2011
East Japan THU001978 Miyagi‐Oki

1

2

3

Period T(sec)Fig. 35%-damped acceleration response spectrum and comparison with past major earthquakes

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OUTLINE OF DAMAGE TO RC SCHOOL BUILDINGS IN MIYAGIDamage Statistics

Number of Building

The Japanese seismic design codes for reinforced concrete buildings were revised in 1971 and 1981.
Specifications such as maximum spacing of hoops of reinforced concrete columns were revised toincrease structural ductility in 1971, whereas the verification on the ultimate lateral load carrying
capacity of designed structure by limit state or pushover analysis considering deformation capacity ofmembers was required in 1981.
In Japan, seismic capacity evaluation and strengthening have been widely applied to existing buildings
especially after the 1995 Kobe Earthquake. By the 2011 East Japan earthquake, all school buildings inmain cities of Miyagi Prefecture were seismically evaluated and most of vulnerable buildings wereretrofitted ( see Fig.4).
Fig.5 shows the damage ratio of 151 reinforced concrete school buildings located in Kobe city in 1995
Kobe Earthquake. Most of the buildings, which suffered from serious damage, were designed andconstructed before 1981, and especially those before 1971 had extensive damage. On the other hand,most new buildings designed according to the current seismic codes enforced in 1981 showed fairly
good performance and prevented severe structural damage. Fig.6 shows the damage ratio of 538 RC
school buildings in main cities of Miyagi Prefecture suffered from the 2011 East Japan Earthquake.
The buildings suffered from tsunami and damage of the foundation were excluded in the figure. There
were no collapses. Although there are few buildings suffered from over moderate damage, the effect ofseismic retrofit can be obviously found in comparing with seismically retrofitted and un-retrofitted
buildings. In addition, the ratio of serious damage for post-1981 or retrofitted is much smaller than thatin 1995 Kobe Earthquake, it suggest that ground motion in 2011 East Japan Earthquake was not severe
as 1995 Kobe Earthquake.
35

Current Building Code30

Evaluated Safficient Capacity
Seismic Retrofitted

25

Not yet Retrofitted

20
15
10
5
0
60

64

68

72

76

80

84

88

92

96

0

04

08

Construction Year

Fig. 4 Construction year and progress of seismic retrofit of investigated RC school building
in main cities in Miyagi Prefecture

Fig.5 Damage ratio of RC school building in 1995 Kobe earthqauke1123

Fig. 6 Damage ratio of RC school buildings of main cities of Miyagi Pref. 2011
Relationship between Seismic Capacity and Damage
Fig.7 shows the relationship between the seismic capacity index (Is-Index) and construction age of 32
RC school buildings, where Is-Indices of each building are evaluated according to the “JapaneseStandard for Seismic Capacity Evaluation of Existing Reinforced Concrete Building”(JBDPA 2001b).
Is-Index can be calculated by Eq.(1) at each story and each direction.
Is  E 0  S D  T(1)

E0 is a basic structural index calculated by Eq.(2).
E0    C  F(2)C-Index is strength index that denotes the lateral strength of the buildings in terms of shear force
coefficient. F-Index denotes the ductility index of the building ranging from 0.8 (extremely brittle) to
3.2 (most ductile), depending on the sectional properties such as bar arrangement, member proportion,
shear-to-flexural-strength ratio etc. Ø is story index that is a modification factor to allow for the modeshape of the response along the building height. SD and T are reduction factors to modify E0 in
consideration of structural irregularity and deterioration after construction, respectively.
The Seismic Evaluation Standard recommends as the demand criterion that Is-Index higher than
0.6 should be provided to prevent major structural damage or collapse. This criterion is based on thecorrelation study from the past earthquake damage and the calculated indices for the damagedbuildings(Okada 1998). Past experiences of damaging earthquakes reported that buildings with
Is-Indices higher than 0.6 escaped severe damage or collapse. Is-Index of school buildings isdemanded higher value (0.7) than normal buildings. It is because that school buildings require not only
the security of safety but also the security of function to use buildings without repairing structural
damage after big earthquake. Figures 7 and 8 show all the buildings with Is-index lower than thecriteria suffered from severe damage. As mentioned earlier, over 90% of RC school buildings havebeen already seismically retrofitted, Is-Indices for most of the buildings were more than 0.7 andprevented severe structural damage even if they were old buildings. Fig.8 shows the relationshipbetween Is-Index and damage level indices R-Index proposed in “Standard for Post-earthquake
Damage Level Classification of Reinforced Concrete Building” (JBDPA 2001a). A good correlation
was observed between calculated Is-index and observed damage. Most buildings with Is-values lower
than 0.6 were vulnerable to moderate and severe damage. Most of the buildings with Is-values higher
than 0.7 avoided severe damage and had minor or slight damage (residual seismic capacity ratio R>
80). Is-Index of 0.7 is generally regarded as an effective demand criterion for screening seismicallyvulnerable buildings.

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Slight or Non
Minor
Moderate
Severe
1965
1970
1975
Construction Age

1980

1985

Residual seismic capacity ratio, R[%]

Is-Index

0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1960

100
90
80
70
60
50
40
30
20
10
0

Fig. 7 Construction age and Is-Indices of RC
school buildings

SlightMinor
Moderate

Severe0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Is-Index

Fig. 8 Is-Indices and damage indices

TYPICAL OBSERVED DAMAGE
In this chapter, some typical damage observed by author’s field survey in Miyagi pref. which is
conducted mainly as an activity of the AIJ committee is described. The damage is classified into 2
main classes; Damage by tsunami and damage by ground motion.
Damage by Ground motion
Severely damaged buildings
Comparatively, the percentage of severely damaged building of the investigated school buildings is not
greater than previous damaging earthquakes such as 1995 Kobe Earthquake. Some of the severely
damaged buildings are mentioned below.
Fig. 9 shows 3 storied RC school building in Shitigahama town built in 1966. Seismic capacity
Is-index of the building was evaluated much lower than the criteria of 0.7. Seismic retrofit wasplanned for the buildings, however, it was not yet conducted before the earthquake. Many ofcolumns and shear walls failed in shear as shown in figure 10and figure 11.

Fig. 9 Overall view ofdamaged school building

Fig. 10 Shear failure
in column

Fig. 11 Shear failure in
shear wall

Seismically retrofitted buildings and seismically evaluated buildings
Most of the existing buildings in Miyagi prefecture which were designed according to the old seismiccode were retrofitted. In general, seismically retrofitted buildings performed well against thisearthquake. However, few buildings had moderate or severe damage. Some cases were chosen for
detailed investigation.
Figure 12 shows 9-story steel reinforced concrete (SRC) building of Civil Engineering andArchitecture building in Tohoku University constructed in 1969, which suffered from minor damage
due to the 1978 Miyagi Oki earthquake. Small shear cracks and flexural cracks were observed inexterior shear walls, adjacent beams and few columns in the 3rd and 4th floor as shown in figure15(a)(Shiga 1980). Acceleration records were obtained by BRI both in 1st and 9th floor of the building.

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Fig. 12 Civil Engineering Building in
Tohoku Univ.

Fig. 13 Typical floor plan and outline of retrofit

Originally, seismic capacities Is-indices were insufficient for the criteria of Is =0.7 as shown in
Table 2. Table 2 shows Is-indices in transverse direction (Y-direction) in lower stories. There exist
many residual cracks induced by previous earthquakes such as 1978 Miyagi Oki earthquake so thatquite low age factor T=0.85 was employed in the evaluation. As can seen in Table 2, C-index, which islateral strength of the building in terms of story shear coefficient, is relatively low but large ductility
was estimated. In 2001, the building was seismically retrofitted by installing framed steel braces in thelongitudinal direction, replacement of RC shear walls in transverse direction and jacketing of adjacentbeams with steel plates (see Fig. 13). The main scheme of the seismic retrofit was mainly to increase
lateral strength and ductility of the structure. The building was estimated as a relatively ductile
structure, so that ductile members were selected for new installing elements in seismic retrofit.
Although seismic capacities Is-indices after retrofit exceeded the criteria of Is=0.7, as shown in Table
3, C-indices for most ductile member group were about 0.3, which in minimum requirement of baseshear coefficient for RC ductile moment frame structures.
Even though it was retrofitted, it was severely damaged by the 2011 earthquake as shown in figure
14(b). There was strong ground motion at the site at periods close to 1 sec (see Fig.15), which is thefundamental vibration period measured for this building during the earthquake. Boundary columns
failed in compression and the connection of walls to beam also failed indicating that the ductility ofthe shear walls was not increased as expected in the seismic retrofit. This may have been caused bypoor connections between the wall webs (which were replaced during the retrofit) and the surrounding
beams and columns.

(a) 1978 Miyagi Oki Earthquake(b) 2011 East Japan Earthquake
Fig.14 Crack pattern of building in Tohoku University

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Table 2 Seismic evaluation before retrofit
for the Y-direction (short direction
direction)
Floor
C
F
No. (groups) (groups)
1
2

3

4

0.17

1.27

0.19

3.26

0.35

1.27

0.18

3.50

0.01

1.27

0.16

2.00

0.21

3.50

0.14

2.00

0.24

3.50

E0

SD

T

Is

Table 3 Seismic evaluation after retrofit
for the Y-direction ( short direction)
Floor
C
F
No. (groups) (groups)
0.2
0.03
0.01
0.22
0.21
0.09
0.32

1.27
2.00
3.34
3.50
1.27
2.00
3.50

3

0.20
0.03
0.27

4

0.13
0.29

0.69 0.9 0.85 0.53

1
0.71

1

0.85 0.60

0.67

10.85 0.57

0.69

10.85 0.59

2

E0

S D CT .S D T

Is0.81 0.9

0.2

1

0.730

1.06

1

0.32

1

1.06

1.27
2.00
3.50

0.82

1

0.27

1

0.82

1.27
3.50

0.86

1

0.29

1

0.86

T=0.5 sec

T=1 sec

1.4

Electrical Eng
building

Shear Walls

Spectral Acceleration, Sa /g

1.2
1h= 5% damped

0.8
0.6

T=2 sec
Civil Eng building

0.4
0.2
0
0

10

20

30

40

50

Spectral Displacement,Sd（cm）

Fig.15 Response spectra of Tohoku university NS(a) Coupled shear wall and link beam(b) Close up of shear failed coupling beam

Fig 16 Electrical building in Tohoku University
Fig. 16 shows another building severely damaged in Tohoku University. This building is 8-story
reinforced concrete building of electrical engineering building constructed in 1969. Electrical buildingin Tohoku Univ. was also retrofitted 1997. A base shear-displacement curve produced by a seismic
evaluation indicated that response of this building was expected to be linear (see Fig.15). Note that thebeams were assumed not to be vulnerable to shear failure and base shear was dominated by theresistance of the shear walls. Collapse was successfully prevented and no one was injured. Although1127

damage to structural walls and columns was light, damage to beams was severe (see fig.17). Penthouse
was also severely damage (see Fig.18) Demolition was decided because of high repair cost.

Fig 17.

Fig. 18 Collapse of penthouse

Shear failure in short beams

Figure 19 shows 3 storied RC building of an elementary school in Sendai city constructed in
1974. The building is divided by expansion joint into west side and east side. Seismic evaluation was
carried out to both sides. According to the seismic evaluation, the East side building needed to be
retrofitted (see fig. 22) and the West side was evaluated to have enough seismic capacity and no
retrofitting was needed. The Is-index for West side building depends on ductility (F=1.75) to reach theof Is> 0.7 which is the criteria in Japan (see Fig. 21). The East side building was retrofitted by adding
framed steel braces and shear walls. By this earthquake, the retrofitted building had only minor
damage. On the other hand, the West side building had shear failure in its short columns as shown infigure 20. Shear failure of those short columns was allowed in the seismic evaluation because axial
loads could be redistributed to other columns and the building didn’t collapse. This building wasn’t
retrofitted since it’s judged that there is no threat to life safety. However, the school could not use thisbuilding after the earthquake and repairing expenses would be relatively high if compared to theretrofitting expenses for a better performance. This issue of functionality is one of important issues
that require more attention. The response spectrum of this area is mentioned above in figure 3 as 2011
East Japan MYG013 NS.

Fig.19 North view of school building

Fig.20 Shear failure in column

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Is index chosen at F=1
about 0.4% story drift

Fig. 21. 1st story seismic evaluation
results of West side Building

Fig.22.

1st story seismic evaluation resultsof East side Building

Damage of Buildings designed according to the current seismic code
All the school facilities in Sendai city were either designed with the current seismic code or have been
already seismically evaluated and retrofitted if necessary. Severely damaged buildings which may be athreat to life safety were not observed in this survey. However, Moderate damage to some buildings
designed according to the early versions (early 1980s) of the current seismic design code was observed.
Figure 23 shows a typical example of a four storied elementary school building constructed in 1985.
This building had a shear failure in one of its walls as shown in figure 24. Beams with shear failure
were also noticed as shown in figure 25.

Fig.23. North view of building

Fig. 24 Shear failure in wing wallFig.25 Shear failure
in beamDamage to non structural elements:
Major damage to non structural elements was observed even in buildings designed according tocurrent seismic design code, although the damage in its structural members was commonly minor.
This damage was likely to be observed in high-rise housing buildings.
In figure 26, large parts of ceiling fell in a gym of a junior high school in Kurihara city fell down.
Figure 27 shows a damaged masonry wall of which some concrete blocks fell down. Such damage
could be a life threat.

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Fig. 26 Large parts of the false ceiling fell down

Fig. 27 Partial collapse of concrete blocks
partition wall

Damage to foundations
Settlement and tilting of buildings as a result of liquefaction had occurred in some regions of Miyagi
prefecture. Figure 28 shows a junior high school building in Osaki city. The right side of the building
was constructed in 1978. The left side was added in 1991. This school rests on a soft ground with pilefoundation of 20m in depth. Evidence of liquefaction was seen around the school as shown in Fig. 29.
The right side part had a settlement of about 60 cm, the south part was inclined by angle of 1/25 rad.
The newly added part had a settlement of about 10 cm and slightly inclined. The response spectrum of
this area is mentioned above in figure 3 as 2011 East Japan 4B9 NS.

Fig. 28 Settlement of school building inOsaki City

Fig. 29 Liquefaction evidence located 3
stair steps from the ground surface.

Damage by Tsunami
The Northeast coastal areas have been heavily damaged by Tsunami. However, as for reinforced
concrete structures, most of the damage due to tsunami was in non structural elements such as false
ceilings, window and doors.
Figure 30 shows a high school building in Kesennuma city. The flooding reached 3rd floor.
Windows, doors ceiling were washed away and classrooms were full of debris.
Figure 31 shows a floor slab that was lifted up and damaged at connections with beams in Ishonamaki
city.

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Fig. 30 Flood reached 3rd floor

Fig. 31 Slab uplifted and dismantled from beam
CONCLUSION

This paper presented the investigation of reinforced concrete building structures. Japanese RC
building showed good performance for saving lives on Great Japan EQ. However, a number ofretrofitted buildings and buildings that had been evaluated to be safe had to be evacuated after theearthquake. Some of these buildings are going to be demolished because the repairs are too costly.
This issue is one that requires attention.
Good correlation was observed between calculated seismic capacity Is-index and observed damage.
Most of the buildings with Is-values lower than 0.6 were vulnerable to moderate and severe damage.
Most of the buildings with Is-values higher than 0.7 escaped severe damage. Moreover, buildings
designed according to current seismic design code had minor damage in structural members. However,major damage to non structural elements was seen even in new buildings.
Damage to structural members was not found in most of RC buildings which suffered tsunami,
although damage to non structural elements such as windows, partitions, ceiling boards andequipments was generally severe. However, severe structural damage induced by devastating tsunami
was observed. Structural design against tsunami force, which is not taken into account in the current
design code, needs to be studied.
Data from buildings (including structural drawings and earthquake records) that had been
evaluated and retrofitted were obtained. Such data give opportunities for future research to improve
the reliability of seismic performance evaluation methods and to define better reparability andservecibeality limits.
REFERENCES
Architectural Institute of Japan (AIJ). (2011), Preliminary Reconnaissance Report of the 2011
Tohoku-Chiho Taiheiyo-Oki Earthquake (in Japanese), Maruzen, JapanBRI Strong Motion Observation, http://smo.kenken.go.jp/ja/smreport/201103111446/
Japan Building Disaster Prevention Association(JBDPA). (2001a). Standard for Post-earthquake
Damage Level Classification of Reinforced Concrete Building.
Japan Building Disaster Prevention Association(JBDPA). (2001b). Standard for Seismic Evaluation of
Existing Reinforced Concrete Buildings.
JMA,http://www.seisvol.kishou.go.jp/eq/kyoshin/jishin/110311_tohokuchiho-taiheiyouoki/index.html
NIED K-NET, http://www.k-net.bosai.go.jp/k-net/
OKADA, T., KABEYASAWA T.，NAKANO Y., MAEDA M.，and NAKAMURA T.(2000).
“Improvement of Seismic Performance of Reinforced Concrete School Buildings in Japan -Part 1
Damage Survey and Performance Evaluation after 1995 Hyogo-ken Nambu Earthquake-”，
Proceedings of 12th World Conference on Earthquake Engineering，paper No.2421（CD-ROM）.
Shiga T.,(1980).”performance of the building of faculty of engineering, Tohoku University, During the1978 Miyagi-Ken-Oki Earthquake”, 7th WCEE Instabul.

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