Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, JapanDAMAGE SURVEY ON BUILDINGSAND THE LESSONS FROM
THE 2011 EAST JAPAN EARTHQUAKE
Toshimi KABEYASAWA
Professor, Earthquake Research Institute, University of Tokyo,
Tokyo, Japan, kabe@eri.u-tokyo.ac.jp

ABSTRACT: Damage survey on buildings is outlined, which was conducted as a part ofreconnaissance activity of AIJ, Architectural Institute of Japan after the 2011 East Japan
Earthquake. Typical types and levels of damages to building structures are classified,both by the ground motions and the tsunami waves, based on the field observation dataon buildings in the affected regions. The damage rates in the selected area are analyzed
and discussed based on the statistical data of the inventory damage rates, as well as inrelation with calculated seismic performance indices.
Key Words: damage survey, reinforced concrete, school buildings, damage evaluation,
seismic evaluation, strengthening

INTRODUCTION
Typical damages to buildings, especially to reinforced concrete buildings, both by the ground motions
and the tsunami waves during the 2011 East Japan Earthquake, are outlined in the paper. The fieldsurvey was conducted in the first stage individually by research institutes or groups also as themembers of AIJ, especially as the members of reinforced concrete steering committee, Architectural
Institute of Japan. The report herein is mostly based on the individual survey by the author in
Fukushima region but also partially referring to the manuscripts by the group members for the
preliminary reconnaissance report of AIJ (AIJ, 2011).
Reinforced concrete buildings surveyed by AIJ teams were categorized into the following fourgroups based on the intended use as: (1) school buildings and community centers, (2) public buildings( mainly government offices), (3) residential buildings, and (4) commercial buildings. The surveyedbuildings are not comprehensive especially for the commercial buildings or private company offices
and private collective houses, while damaged school buildings and public halls are surveyed mostly
based on the preliminary post-earthquake survey list.
The AIJ organized a special committee and working groups after the earthquake to investigate
damages to school buildings and public halls, also to evaluate the damage levels for the recovery
process of the facilities, which were requested to AIJ officially from MEXT, Ministry of Education.
The committee members conducted the field survey based on the request of the local governments incharge of the facility ad-ministration. More than 700 buildings were surveyed in total: (1) about 400
rein-forced concrete (RC) school buildings, (2) 200 steel or steel concrete composed gymnasiums, (3)186100 others such as timber schools, community centers and public halls with various structural types.
The results of damage investigation above are to be compiled and published from AIJ with thewhole statistical analysis on the surveyed buildings as well as detailed reports on selected buildings
and seismic performance evaluation. In this paper, typical damages observed through the survey of AIJ
and the derived lessons are reported with part of the statistical investigation from the survey.

GROUND MOTIONS AT K-NET STATIONS IN FUKUSHIMA
Ground motions at surface were observed at K-net stations in Fukushima region, which had been
installed and operated by NIED, National Research Institute for Earth Science and Disaster Prevention,from after the 1995 Hyogo-ken-Nambu Earthquake. The acceleration response spectra and the velocity
response spectra are calculated, as shown in Fig. 1 and Fig. 2, respectively, for the main shocks
starting from 14:46, March 11, to estimate input ground shaking to the surveyed buildings below, mostof which were close either of ten stations selected in Fukushima region, such as in Yanagawa,
Fukushima, Haramachi, Iwaki, Nakoso, Shirakawa, Sukagawa, Koriyama, Nihonmatsu, andAizuwakamatsu.
Far field motions by the 2011 earthquake of magnitude 9.0 are compared with near field motions
by recent earthquakes of magnitude around 7.0, as shown in Fig. 3 and Fig. 4. The far field motions
have long duration, more than 120 seconds, and wide range of frequency components, while near fieldmotions have short duration, and with amplified components in the longer period, so that the near fieldmotions are sometimes more effective to responses of medium RC buildings and low-rise timberbuildings.
Although the magnitude 9.0, the epicenter distances were more than 200km－400km, so that theintensities were almost close to design level of very rare earthquake, Level 2. The ground motions
recorded during the 2011 Earthquake were smaller less than the extreme motions recorded at recent
near field earthquakes (1995 Kobe, 2004 Niigata, 2007 Niigata). The near field extreme motions (1995
Kobe and 1948 Fukui) might have been twice to three-times higher than the 2011 records, so that
relatively small damages would not ensure the safety in the future. The near field earthquakes occur
once or more every ten year somewhere in Japan, therefore the collapse or severe damages ofbuildings, which might cause the casualty, could still be the major problem in the future earthquakes
more than in cases of the 2011 earthquake.
The responses of damaged buildings might be estimated approximately from these response
spectra, while it should be noted that large errors of the estimation could still occur because of (1)micro-zone site effects, especially due to ground amplification, and (2) essential difference between
the free-field recorded motions and the actual input motions to the structure including soil-structureinteractions.
Acceleration (m/sec/sec)

Acceleration (m/sec/sec)

NSNScomponent

50
45
40
35

)
s/
m
(
n
oi
t
ar
el
e
c
c
A

2

30

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35

)
s/
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(
n
oi
t
ar
el
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A

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20
15

10

10

5

5

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

梁川
Yanagawa,
福島
Fukushima,
原町
Haramachi,
いわきIwaki,
勿来
Nakoso,白河
Shirakawa,
須賀川
Sukagawa,
郡山
Koriyama,
二本松
Nihonmatsu,
会津若松
Aizuwakamatsu

45

25

0

EW com
EWponent

50

Yanagawa,
梁川
福島
Fukushima,
原町
Haramachi,
いわきIwaki,
勿来
Nakoso,白河
Shirakawa,
須賀川
Sukagawa,
郡山
Koriyama,
二本松
Nihonmatsu,
会津若松
Aizuwakamatsu

05Period (sec.)
Period
(sec)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Period (sec.)
Period(sec)

Fig. 1 Acceleration response spectra by the ground motions recorded in Fukushima

187

5

Velocity (m/sec)

Velocity (m/sec)NS
NS component

2
1.8
1.6
1.4

)
s/
m
(
yt
i
c
ol
e
V

1.2
1
0.8

1.6
1.4

)
s/
m
(
yt
i
c
ol
e
V

1.2
1
0.8
0.6

0.4

0.4

0.2

0.2

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

梁川
Yanagawa,
福島
Fukushima,
原町
Haramachi,
いわきIwaki,
勿来
Nakoso,白河
Shirakawa,
須賀川
Sukagawa,
郡山
Koriyama,
二本松
Nihonmatsu,
会津若松
Aizuwakamatsu

1.8

0.6

0

EW
EW component

2

梁川
Yanagawa,
福島
Fukushima,
原町
Haramachi,
いわきIwaki,
勿来
Nakoso,白河
Shirakawa,
須賀川
Sukagawa,
郡山
Koriyama,
二本松
Nihonmatsu,
会津若松
Aizuwakamatsu

0

5

0

0.5

1

1.5

2

Period (sec.
)
Period
(sec)

2.5

3

3.5

4

4.5

5

Period (sec.)
Period(sec)

Fig. 2 Velocity response spectra by the ground motions recorded in Fukushima
Acceleration (m/sec/sec)
55

Acceleration (m/sec/sec)

NS component

50

45

40

35

30

梁川
Yanagawa,
福島
Fukushima,
原町
Haramachi,
いわきIwaki,
勿来
Nakoso,白河
Shirakawa,
須賀川
Sukagawa,
Koriyama,
郡山
二本松
Nihonmatsu,
Aizuwakamatsu,
会津若松
1995
Kobe JMA
兵庫県南部地震（1995，神戸JMA）
2003
Miyagi, Ichinoseki-west
宮城県沖地震(2003,
一関西KiK-net)
2004
Niigata-Chuetsu, Ojiya
新潟県中越地震(2004,小千谷K-net)
2007
Niigata-Oki, Kashiwazaki
新潟県中越沖地震(2007,柏崎K-net)
2008
Iwate, Ichinoseki-west
岩手・宮城内陸地震(2008，一関西KiK-net)

50

45

40

35

30

25

25

20

20

15

15

10

10

5

0

EW component

55

梁川
Yanagawa,
福島
Fukushima,
原町
Haramachi,
いわきIwaki,
勿来
Nakoso,白河
Shirakawa,
須賀川
Sukagawa,
Koriyama,
郡山
二本松
Nihonmatsu,
Aizuwakamatsu,
会津若松
1995
Kobe JMA
兵庫県南部地震（1995，神戸JMA）
2003
Miyagi, Ichinoseki-west
宮城県沖地震(2003,
一関西KiK-net)
2004
Niigata-Chuetsu, Ojiya
新潟県中越地震(2004,小千谷K-net)
2007
Niigata-Oki, Kashiwazaki
新潟県中越沖地震(2007,柏崎K-net)
2008
Iwate, Ichinoseki-west
岩手・宮城内陸地震(2008，一関西KiK-net)

5

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0

5

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Period (sec)Period (sec)Fig. 3 Acceleration response spectra compared with those by recent near field motions
Velocity (m/sec)

Velocity (m/sec)

NS component

5.5

5

4.5

4

3.5

3

4.5

4
3.5

)
/s
m
(
v
S

3

2.5

2

2

1.5

1.5

1

1

0.5

0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Yanagawa,
梁川
福島
Fukushima,
Haramachi,
原町
Iwaki,
いわき
Nakoso,勿来
Shirakawa,
白河
Sukagawa,
須賀川
Koriyama,
郡山
Nihonmatsu,
二本松
Aizuwakamatsu,
会津若松
1995
Kobe JMA
兵庫県南部地震（1995，神戸JMA）
2003
Miyagi, Ichinoseki-west
宮城県沖地震(2003,
一関西KiK-net)
2004
Niigata-Chuetsu, Ojiya
新潟県中越地震(2004,小千谷K-net)
2007
Niigata-Oki, Kashiwazaki
新潟県中越沖地震(2007,柏崎K-net)
2008
Iwate, Ichinoseki-west
岩手・宮城内陸地震(2008，一関西KiK-net)

5

2.5

0

EW component
EW

5.5

梁川
Yanagawa,
福島
Fukushima,
原町
Haramachi,
いわきIwaki,
勿来
Nakoso,白河
Shirakawa,
須賀川
Sukagawa,
郡山
Koriyama,
二本松
Nihonmatsu,
会津若松
Aizuwakamatsu,
1995
Kobe JMA
兵庫県南部地震（1995，神戸JMA）
2003
Miyagi, Ichinoseki-west
宮城県沖地震(2003,
一関西KiK-net)
2004
Niigata-Chuetsu, Ojiya
新潟県中越地震(2004,小千谷K-net)
2007
Niigata-Oki, Kashiwazaki
新潟県中越沖地震(2007,柏崎K-net)
2008
Iwate, Ichinoseki-west
岩手・宮城内陸地震(2008，一関西KiK-net)

0

5

0

0.5

1

1.5

2

2.5
Period (sec.)

3

3.5

4

4.5

Period (sec)Period (sec)Fig. 4 Velocity response spectra compared with those by recent near field motions

188

5

METHOD OF EVALUATING DAMAGE LEVELThe evaluated damage rates were classified into five levels and no damage such as collapse, severe,
moderate, minor, slight and no damage, based on the “Post-earthquake damage evaluation standards,”(JBDPA, 2001a) and described as below. Because the buildings for survey were selected through therequest of the administrators, all the buildings with serious damage such as moderate or more shouldhave been included for damage evaluation. However, a few of them were excluded due to theconfusion of the procedure, while buildings with much less structural damages are included as a result.
Detailed investigations on the design, construction, age and structural drawings were available formost of public buildings, while the investigations on private buildings are limited very much. Also formost of the public buildings, especially on schools, the seismic capacity indices “Is-values” had been
evaluated based on the Standard for Seismic Evaluation of Existing Reinforced Concrete Buildings(2001 Japanese version and 2004 English version) by professional engineers re-quested from theadministrative governments. In the process of the seismic evaluation, concrete strengths had been also
tested with sample cylinders extracted from the existing buildings. Some of the seismic indices or theconcrete strengths are referred with the damage evaluation below, though the detailed results andanalyses with the seismic intensities will be reported elsewhere.
On the other hand, the ground motions have been recorded at K-net stations in the major cities
and JMA intensity scales have been identified officially by Japan Meteorological Agency for more
small zones of municipal area. The seismic intensity sensors are installed mostly in the free field
nearby the city hall buildings. The JMA intensity scales at the site of the damaged buildings arereferred in the report below from these identified values such as 5-, 5+, 6-, 6+ and 7(not recorded in
the 2011 earthquake), which approximately correspond to 8-, 8+, 9, 10 and 11 by the Modified
Mercalli intensity (MMI) scale.
The post-earthquake damage evaluation on the reinforced concrete buildings were conductedbased on “the Japanese standard of damage evaluation in post-earthquake inspection[JBDPA, 2001]”,
by which the damage grade were classified into one of the five grades and no damage estimating theresidual seismic capacity ratio R. The rate of damage is calculated in term of the residual seismic
capacity R, which expresses the ratio of the post-earthquake residual capacity to the pre-earthquake
original capacity, estimated from the observed damage grades of surveyed vertical members.
The vertical members and estimated failure mode are grouped into five types as (1) shear column,(2) flexure column, (3) wall without boundary columns, (4) wall with a boundary column and (5) wallwith boundary columns at both ends, among which the seismic capacity or strength ratios of themember types (1) through (5) are assumed to be 1:1:1:2:6, respectively. The damage rate of eachvertical member is classified into one of none [0] and the five levels from [I] to [V]. The ratios of theresidual capacity are assumed as 1:0.95:0.6:0:0 for the shear column and other wall members, and
1:0.95:0.75:0.5:0.1:0 for the flexural column, in accordance with the damage rates of [0] to [V],respectively.
Then the residual capacity of each story is estimated from the numbers of the vertical memberswith the type classified as above and the evaluated damage rate. If the evaluation is not available forsome of the members, the residual capacity may be calculated only from the surveyed members. The
residual capacity ratio R is calculated for each story and direction, from which the minimum value isadopted to rank the damage grade of the building, such as into the followings: (Grade 0) No damage,(Grade 1) slight, (Grade 2) minor, (Grade 3) moderate, (Grade 4) severe or heavy, or (Grade 5)
collapse or near col-lapse, if the reduction ratio R is (0)100%, (1)95<R<100, (2)80<R<95,(3)60<R<80, (4)R<60, or (5)R seems to be close to zero, respectively.

189

TYPICAL DAMAGES TO BUILDINGS IN FUKUSHIMA
Damages to buildings in north Fukushima
F-college
Collapse of a building, so-called pancake crush, was observed, as shown in Photo 3, in F-college
located north of Fukushima city, which was three-story reinforced concrete building for administration
built in 1965. Although the JMA seismic intensity around the site was classified into V+, the site wasclose to the area of VI lower, and also it was indicated from aftershock observation that the groundmotion might be higher in the site than the center of Fukushima city. The building had a Y-shaped planwith a stair hall in the center and three longitudinal blocks spread to north, east and west directions asequivalent triangular. It is estimated that the concentration or unequal distribution of the lateralearthquake loads might have occurred among the three blocks, due to the difference of the innercolumn heights, by which the severe collapse was induced peculiar to this building.

Photo 1 Damages to F-college building
N-elementary school
Severe brittle failure of a short column at the entrance hall was observed in N-elementary school
3-story RC building constructed in 1968, as shown in Photo 2. The seismic intensity at the site wasestimated as V+ and the seismic performance index was calculated as Is=0.42, though the heavy
damage was concentrated to the short column. Moderate damages to other columns were observed andthe damage level was classified into severe, so that the building is to be demolished and replaced.

Photo 2 Damages to N-elementary school building190

H-high school
Severe brittle failure of short columns in the north frame was observed in H-high school 4-story RC
building constructed in 1970, as shown in Photo 3. The intensity of the motion around the sight was VI
lower. The shear failure is mainly due to less hoop ratio based on the old code, 9φ@250mm. The
damage level was classified into severe and the building is to be demolished. Calculated Is was 0.39 in
the second story and measured concrete strength was 16MPa. The damage level of the other 3-story
building with Is=0.47 was moderate and is to be repaired and strengthened.

Photo 3 Damage to H-high school building
D-Gymnasium
Spalling off of concrete was observed at the base anchorage of roof truss fame in D-gymnasium innorth Fukushima. The structure is reinforced concrete column-wall system with steel truss-frame roof.
The administrator said that the damage of spalling off was induced by the aftershock of April 7, when
refugees occupied the gymnasium to stay day and night. It was fortunate that the refugees barely
escaped from injury during the aftershocks. Also the detailed post-earthquake inspection is necessary
to avoid the secondary damages. Though it is not considered even in the current code, the author havesuspected that much higher expanding forces might have acted to the joint than estimated from design
calculation, not only in this case but also in many other cases, where the steel beams were connectedor anchored to the cantilever columns or walls, which could be induced by the different phases of
responses on the opposite sides, as like as shown in Fig. 5(a). The difference could not be estimatedfrom elastic/symmetric modes but might be possible in inelastic/asymmetric modes with insufficient
stiffness on the roof. The possible maximum forces should be investigated further through analyticaland experimental studies.

Photo 4 Damage to D-Gymunasium

Fig. 5(a) Expanding force on the joint

191

Damages to buildings in middle Fukushima
M-junior high school
Near collapse failure was observed at M-junior high school building, 3-story built in 1966, as shown in
Photo 5, where the JMA seismic intensity recorded as 5+. The shear walls from base to top are locatedas partitions between classrooms in the span direction except for two frames in the first story, as
shown in Fig. 5(b), by which large varying axial loads were generated to the isolated columns during
earthquakes and the near collapse failure was induced.

Photo 5 Damage to M-junior high school building

Fig. 5(b) Discontinuous walls

A-high school
Severe shear failure in short columns are observed in A-high school, 3-story RC building built in 1964.
The structure was bare from original with very low seismic performance index (Is=0.17) and suffered
the severe damage, as shown in Photo 6. The building is to be demolished. The damaged building wasconnected with expansion joint to the adjacent building in west, which had been retrofitted at the timeof the earthquake. The building was originally built in 1966 and the seismic index before retrofit wasevaluated as Is=0.25, which had been strengthened with steel braces exceeding the standard required
level of Is=0.7. The retrofitted west building suffered no damage, as shown in Photo 7. The effect ofretrofit on the actual seismic performance was indisputably evident in the case.

Photo 6 A-high school building (Bare east part, 1964)192

Photo 7 A-high school building (Retrofitted west part, 1966)
K-elementary school
The effect of retrofit was also verified in K-elementary school, which was structurally continuous but
had been partially retrofitted at the time of earthquake. The building was built in 1969, and the barewest part, waiting for retrofit in 2011, suffered severe damage, while the east part had beenstrengthened with steel braces and resulted in no damage, as shown in Photo 8 and Photo 9. In thiscase, the retrofit was found to be effective partially to the frame nearby the strengthening, but the rigid
slab assumption was not much effective in case of the longer building the longer longitudinal size.

Photo 8 K-elementary school building (Bare west part, Severe)

Photo 9 K-elementary school building (Retrofitted east part, No damage)193

S-elementary school
Severe damages to columns to north frame were observed in S-elementary school buildings, consistingof four three-story RC buildings built in 1965, as shown in Photo 10. The JMA seismic intensity was
6+ at the station 1 km east from the school. The Is-value was 0.46 with the space of column hoops was
300mm.

Photo 10 Damages to K-elementary school buildings
S-junior high school
The gymnasium with RC walls and Steel keel beam and roof built in 1985 suffered moderate structural
damage to the joint concrete on the roof, as shown in Photo 11. The joint behavior and the design
should be investigated in detail further as indicated for the damage of D-gymnasium above.

Photo 11 Damages to S-junior high school gymnasium
I-training center
It was not functional in use long time after the earthquake due to damages to ceilings in a gymnasiumof I-training center, which was in accordance with the current code and almost with no/slight structural
damages, as shown in Photo 12.

194Photo 12 Damages to I-training center gymnasium
T-public hall
Structural damages to the south façade in T-public hall were slight though serious damages wereobserved in the third-story conference room with the falling of ceilings, as shown in Photo 13. The
building was built in 1967 up to the second story with RC frames, as a public hall of Tamura city, andthe third story was added in 1980 with RC columns, steel beams and PC lightweight roof-slabs. The
joint concrete at beam ends spalled off, probably due to the out-of-plane expanding behavior of
cantilever columns, which might not had been taken into account in design analysis. The damage was
evaluated as moderate, though the heavy repair construction would be required.

Photo 13 Damages to T-public hall building

Damages to buildings in south Fukushima
S-high school
Damage to a short column was observed in S-high school building, 2-story RC built in 1964, as shownin Photo 14. The intensity of the ground motions in the region was VI+ and relatively high. The
acceleration response spectra recorded in Shirakawa exceeded 4G at around the period of 0.25 sec.,
which might be estimated not to be effective to the damages to the buildings.

195

Photo 14 Damages to S-high school building
Damages to buildings in east Fukushima (Minami soma)
S-elementary school
Damages by Tsunami wave were observed in S-elementary school building, 2-story RC built in 1975
and gymnasium, RC with steel roof, built in 1992. The height of the Tsunami wave was up to 1.6m at
the site in Minami-soma, which was located about 3km west from the coast, as shown in Photo 15.

Photo 15 Damages to S-elementary school building and gymnasium
Damages to buildings in south-east Fukushima (Iwaki)
IK-high school
Damages by Tsunami wave was observed in IK-high school buildings, originally as fisheries highschool, 3-story and 4-story RC main buildings built in 1979-80, as shown in Photo 16. The height of
the Tsunami was up to the ceiling of the first story of 3.5m, where the site was located along the coastof south Iwaki. The structural damages were not observed in the RC buildings. Heavy damages toexternal walls were observed in other twenty buildings, one- or two-story, RC or steel structures, while
structural members remained though residual deformations are observed in some steel members, as
shown in Photo 17.

196

Photo 16 Damages to IK-high school RC buildings

Photo 17 Damages to IK-high school buildings
I-high school
Relatively severe damages of near collapse were observed to the columns in I-high school buildings asshown in Figs. 18 through 20. Four RC buildings with 4-/3-/2-/2-story were constructed from 1973 to
1975. The column hoops were 13mm bars at the spacing of 100mm. The seismic indices Is-values had
been calculated as 0.59, 0.64, 1.08 and 1.44. It was expected from these values that the damages would
not be so heavy under the main shock of the seismic intensity 5- around. However, it was also
expected that the high amplification of the ground motions could be induced due to the hill site effect.
Actually observed damages were relatively severe or moderate with the residual seismic capacity of
R=33, 47, 73, 72%.

197

Photo 18 Site on the hill of I-high school buildings

Photo 19 Damages to I-high school buildings

Photo 20 Damaged columns in I-high school buildings

AFTERSHOCK OBSERVATION
The author’s laboratory have conducted series of aftershock observations after recent major
earthquakes in Japan, such as 2004 Niigata-Chuetsu, 2007 Niigata-Oki, 2008 Iwate-Nairiku at various
sites around buildings for damage survey. The objectives of the observations were to estimate or
identify (1) local site effects, (2) input loss of the ground motions, and (3) response characteristics of198

the buildings, which have brought quite successful data to verify these effects on site. Therefore, a setof three points for observation at one site will be ideal though the number of available seismographs islimited: (1) at free-field surface on site, (2) at the base of the building, and (3) at the roof of thebuilding. If possible, it would be much more preferable idea that a temporary observation site could be
added at deep underground and so on.
The aftershock observations were also spread out at various sites after the 2011 earthquake inparallel with the damage survey with the same objectives. The detailed results will be reported
elsewhere, while an example of the results is shown in Fig. 6 for the site of I-high school described asabove, where the acceleration and velocity response spectrum of the aftershocks recorded at the top of
the hill(Nogyo) and the bottom of the hill(Kogyo) on April 11 are compared in the figure. It was
obvious that the response spectrum at around of the period of 0.6 second was much amplified at thehill top, especially in EW component by several times. Although the ratio of the main shock might
have been smaller than in case of aftershock for due to the non-linear soil responses, it would benecessary to take the local site amplification into account, such as by 1.5 or 2.0 times, if the newbuildings are to be designed and constructed in the rehabilitation procedure.
Aftershock, 17:16, April 11, 2011

Aftershock, 17:16, April 11, 2011
140

Kogyo-1F_EW
Kogyo-1F_NS
Kogyo-FF_EW
Kogyo-FF_NS
Nogyo-FF_EW
Nogyo-FF_NS

1400
1200
1000
800

Velocity response (cm/s)

Acceleration response (gal)

1600

600
400
200

Kogyo-1F_EW
Kogyo-1F_NS
Kogyo-FF_EW
Kogyo-FF_NS
Nogyo-FF_EW
Nogyo-FF_NS

120
100
80
60
40
20

0

0
0

0.5

1

1.5

2

2.5

3

Period (s)

0

0.5

1

1.5

2

2.5

3

Period (s)Fig. 6 Response spectra of aftershocks at the sites at the top and the bottom of the hill

INVENTORY DAMAEGE RATES OF RC SCHOOL BUILDINGSThe total number of the school buildings and other educational facilities for the survey by the AIJ
teams was about 700, which were widely distributed over nine prefectures in Tohoku and Kanto area.
The list of the buildings for AIJ survey were based on the requests from the local governments through
MEXT, which were selected to determine the rehabilitation procedure, esp. for the damage levelevaluation based on the post-earthquake quick inspection the government and engineers. The selectedbuildings had any damages, even slight or minor, structural or non-structural, though the damagelevels of the buildings for survey were widely varied. Also some of the local governments could not
respond to the call of MEXT in confusion, or some did not include minor or moderate damages into
the list, though it was expected that most of relatively or apparently heavy/moderate damages havebeen included in the list. Therefore, we have to be careful to derive the damage statistics, especiallythe inventory damage rates in terms of the damage ratios to the whole existing buildings, whether theinventory damages have been identified and the whole buildings are selected appropriately as aparameter in the area.
At this stage, it is still difficult to drive meaningful damage rates for all the surveyed data, though
the damage rates are summarized here tentatively and partially for school buildings under theadministration of Fukushima prefecture, consisting of all public high-school buildings, including
special school buildings for disabled students, 900 buildings in total. The other damage rates and199statistical analysis on elementary/junior-high schools and public halls are to be published from AIJ in
March 2012, though further detailed investigations need be continued for more years.
A set of parameter was as reinforced concrete buildings out of all prefecture school buildings:
440 buildings in total and 307 buildings built before 1982. Damage levels were evaluated for 62
buildings out of them, such as severe, moderate, minor, slight/no damage, tsunami, and out of survey.
The damage rates in total are shown in Fig. 7, while regional distributions are shown in Figs. 8 and 9.
A set of parameter was taken as the RC buildings of 440 above, or the buildings of 307 built before
1982 out of them. Even minor damages were not reported on the RC buildings constructed after 1981,
though some damages were reported on steel gymnasiums even constructed after 1981, which will be
discussed in detail elsewhere. Although some damages might be overlooked, especially on newbuildings, it was much reliable that the data on the school buildings under Fukushima prefecture thanthe other data.
It should be noted that the major structural damages were not reported to 88 RC high-schoolbuildings in Aizu region, while 26 buildings have not been inspected nor evaluated in Soso region(Futaba, Namie, Tomioka, Iidate, Shinchi and Odaka of Minami-soma), evacuation area from theaccident of TEPCO-NPP, where the entry has still been restricted for ten months after the accident.
The ratio of minor to severe damages in total, where the buildings were basically not functionalin use, was about 6% to total and 8% to the buildings before 1982. Because these are is based with aparameter including Aizu and Soso, therefore if the two regions are excluded from the parameter, thenthe ratios are 8% and 12% respectively. As for the buildings classified into the grade of severe, whichwere to be demolished and rebuilt rather than repaired, the ratios were 1.1% to total, 1.6% to pre-1982,
1.5% to those without Aizu and Soso, 2.2% to pre-1982 without Aizu and Soso. Considering theintensities of the ground motions were close to the very rare level of BSL, level 2, in most regions, it
may be concluded that these damage rates were satisfactorily low. This was partially owing to theseismic strengthening of school buildings, although it had been behind in Fukushima prefecture, which
will be discussed later in this paper. Other reasons also lie in discrepancy with the standard
requirement of seismic evaluation and the actual response behavior.
As for the regional distributions, the damage rate was obviously small in Aizu region while
relatively higher in Iwaki region. These are partially because of the earthquake intensity including thesite effects and distance to the sources, especially to the Off-Iwaki source, though these were not muchclear by K-net motions shown in Figs 1 to 4. It is also presumed for another reason of lower damages
in Aizu region that the design seismic force is relatively higher including the permanent snow loads inthe region.

Out of survey
TsunamiSlightMinor
Moderate
SevereDamage rates for all RC

Damage rates, agaist RC buidings before 1982

Fig. 7 Inventory damage rates for all prefecture school buildings

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Out of survey
TsunamiSlightMinor
Moderate
SevereRC school buildings (prefecture schools)

Out of survey
TsunamiSlightMinor
Moderate
Severe

Soso
Aizu
Iwaki
Soma
South
Middle
North
0

20

40

60

80

100

120

Fig. 8 Regional distribution of inventory damage rates for all prefecture school buildings
RC school buildings (prefecture schools before 1982)
Out of survey
TsunamiSlightMinor
Moderate
Severe

Soso
Aizu
Iwaki
Soma
South
Middle
North
0

20

40

60

80

100

120

Fig. 9 Regional distribution of inventory damage rates for prefecture school buildings before 1982

RELATIONS BTW DAMAEGE RATE AND SEISMIC PERFORMANCE
Seismic performance evaluation of existing school buildings, as well as strengthening if required, havebeen implemented into practice, especially after 1995 Kobe earthquake, required by the law on “thepromotion of seismic strengthening,” which have been applied to public buildings and largecommercial buildings open to public after 1995. If the seismic performance indices of old building
constructed before 1982 are lower than the standard required level, they have to be strengthened up to
the level or higher at the time of renovation or expansion. The seismic evaluation and the seismic
strengthening of school buildings have been promoted by the local governments with the financial aid

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of MEXT, so that the ratios of the buildings exceeding the standard requirement to the whole existingbuildings, hereafter called the seismic safety ratios, have been increasing about 5 percent per year, andthe averaged ratios all over Japan have attained 80% for elementary/junior-high public schools, and
77% for high schools at the end of March 2011. The seismic safety ratios of school buildings at thetime of the earthquake might have been close to these values averagely in Japan though the regional
distributions are varying among prefectures.
As for the seismic performance indices Is of the RC buildings in high schools and special schools
in Fukushima prefecture, they have been ranked into the grades of A to D, such as A(Is>0.7) requiring
no retrofit, B( Is>0.7), B’(0.6<s<0.7), C(0.3<Is<0.6) and D(Is<0.3) requiring retrofit. The Is-values ofthe buildings have been ranked before and after the strengthening for retrofit with the buildings
constructed after 1981, which had been regarded as to conform to the current code of practice, andclassified as S. The seismic performance of the buildings after 1981 have been regarded as exceeding
the safety requirements in the seismic performance evaluation standard without any evaluation
procedure so far, however the detailed and rigorous evaluation might be necessary in the future,especially for buildings designed and constructed before 1995.
If the seismic safety ratio of the RC school buildings were defined as the sum of the ranks S andA, then the ratio was around 50% before the strengthening started and had been upgraded up to 62%
by the retrofit at the time of earthquake, as shown in Fig. 10. The regional distributions of theseseismic performance ranks are shown in Figs. 11 and 12, also before and after retrofit. It might beconcluded that the safety ratios are relatively higher in Aizu, Soma and South regions with few rank D,
where the damage ratios in Figs. 8 and 9 were generally smaller.
The direct relations are plotted in Fig. 12 between the observed damage level in terms of theresidual capacity R and the calculated seismic performance level in terms of the structural seismicindex Is-value. The unknown R is assumed as 99%, which might not be different much, even if
evaluated, while the unknown Is is assumed as zero, which is to be disregarded. Positive correlations
are observed between Is and R generally. It should be noted, however, in cases of the marks withdotted circles, that R is lower than 80% even if the Is is much higher or around 0.6. Four of these are
the buildings of I-high school on the hill in Iwaki described above, and a building in S-special schoolin middle region, where the ground motions might have been higher there due to some local site
effects. Detailed model and analysis are needed to simulate the damage level in relation with theestimated input motions.

S（1982-)
A(>0.7)
B(>0.7)B'(0.7-0.6)
C(0.6-0.3)
D(<0.3)
Unknown
Seismic performance indices (before retrofit)

Seismic perofrmance indices (after retrofit)

Fig. 10 Seismic performance indices before and after retrofit

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S（1982-)
A(>0.7)
B(>0.7)B'(0.7-0.6)
C(0.6-0.3)
D(<0.3)
UnknownPrefectural RC school buildings (before retrofit)

S（1982-)

Soso

A(>0.7)
Aizu

B(>0.7)B'(0.7-0.6)

Iwaki

C(0.6-0.3)
D(<0.3)

Soma

UnknownSouth
Middle
North
0

20

40

60

80

100

120

Fig. 11 Regional distribution of seismic performance indices before retrofit

Prefectural RC school buildings (after retrofit)

S（1982-)

Soso

A(>0.7)
Aizu

B(>0.7)B'(0.7-0.6)

Iwaki

C(0.6-0.3)
SomaD(<0.3)
UnknownSouth
Middle
North
0

20

40

60

80

100

120

Fig. 12 Regional distribution of seismic performance indices after retrofit

LESSONS FROM THE DAMAGES AND DESIGN IMPLICATIONS
Summary of the observed damages and their reasons
As a result of survey, typical damages to reinforced concrete school buildings from the 2011
Earthquake may be summarized as follows with estimated reasons:(1) Several buildings suffered very serious damages, such as collapse or severe, which requires
demolish and reconstruction for restoration, although the rate was very low.

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R

Relations between Is and R
10050: I-high school in south-east region: S-special school in middle region
0
0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

Is

1.4

1.5

Fig. 13 Relations between the seismic performance indices Is and the damage rates
in terms of the residual capacity R (%)(2) Numbers of buildings suffered moderate or minor damages, by which they were not functional incontinual use and requires repair or strengthening.
(3) The damaged RC buildings of high schools were constructed before 1981 when the current code
was put into practice.
(4) Shear failure of columns, especially of short columns, was observed probably due to insufficient
rate of hoops, concentration of earthquake load or high varying axial load.
(5) Relatively heavy damages are observed at the joint concrete with steel and/or timber members inconcrete structures combined with steel or timber members.
(6) Most of the new buildings designed by the current code or older buildings retrofitted to thecurrent required level suffered relatively slight or minor damages.
(7) Non-structural walls and ceilings were severely damaged in many cases, not only with old but
also with new buildings.
(8) Damages seemed to be increased by the amplification of ground motions due to soils and hills,
was observed and the effect was clearly verified through aftershock observation.
(9) Settlement of base foundation due to damages to piles or soils or liquefaction were observed,
which could not be introduced in this paper.
(10) Not only non-structural but also structural failures due to the tsunami waves were observed in RC
buildings, from which the rehabilitation seemed to be difficult in most cases.
Design implications and further research needs(1) Collapse and severe damages would be induced due to lack of the hoop ratio in the columns, loadconcentration, long span and high varying axial load by interrupted walls in the old buildings.
The current seismic evaluation procedure would efficient to simulate these possible damages.
(2) Design forces at the joints of concrete walls/columns and steel beams might be insufficient, even

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(3)

(4)
(5)

(6)
(7)

(8)
(9)

in the current design code. Further analytical and experimental studies are needed on the problem.
Also engineers should ensure sufficient stiffness of steel members to preserve integral response
behavior.
Amplification of the ground motion peculiar to the site, especially by the hill, should be taken
into account, in reconstruction and design of buildings after demolish of damaged buildings.
Seismic micro zoning with soil condition and observation on site would be useful in design.
Pile and foundation need ultimate state design to prevent damages to foundations withconsideration of non-linear soil-structure interaction.
Ceiling and non-structural walls need the sufficient specifications on detailing or structural
calculation in new design to prevent damages and falling down. The transparent evaluation
method for those in old buildings is also needed.
Structural plan to add strength in longitudinal direction using walls and wing walls
Current seismic strengthening method was effective to improve the seismic performance ofschool buildings so that dissemination of seismic retrofit, esp. with economical methods, areessential to residential or commercial buildings also.
Location plan and design against possible tsunami waves are required for the buildings in thetsunami-affected regions.
Extreme motions from near sources should be considered not only to ensure safety but alsofunctionality in use for school buildings, which would have much higher intensity than observedin the 2011 earthquake.

CONCLUSIONS
The results of AIJ damage survey on RC school buildings after the 2011 East Japan Earthquake arereported. Typical types and levels of damages to building structures are classified based on the fieldobservation data on buildings in the affected regions. The damage rates in the selected area are
analyzed and discussed based on the statistical data of the inventory damage rates as well as in relation
with calculated seismic performance indices. The lessons and design implications from the observed
damages and analysis are summarized.

ACKNOWLEDGMENTS
The field survey was conducted as the reconnaissance activity of Architectural Institute of Japan, from
April to June 2011, which was requested from the local governments through MEXT, Ministry of
Education as part of the rehabilitation procedure on the damaged school buildings. The voluntary
activities of the committee members of AIJ, the clerical supports of the staffs in the local governments
and MEXT and the technical support of practical engineers on the field survey are gratefully
acknowledged. Some of the statistics, esp. on seismic evaluation of school buildings, are based on theclosed data within Fukushima prefecture provided to the author in the process of damage evaluation.
The efforts of the engineers and staffs involved in the seismic evaluation and strengthening practices
are also gratefully acknowledged.

REFERENCESJBDPA(2001a), "Standard for Damage Level Evaluation and Guidelines for Recovery Technologies of
Buildings Damaged by Earthquake (in Japanese)," Japan Building Disaster Prevention
Association, 360pp.
JBDPA(2001b), “Standard for Seismic Evaluation of Existing Reinforced Concrete Buildings (2001Japanese version and 2004 English version),” Japan Building Disaster Prevention Association.

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