Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, JapanDAMAGES TO REINFORCED CONCRETE
BUILDINGS OBSERVED IN FUKUSHIMA AFTER
THE 2011 EAST JAPAN EARTHQUAKE
Toshimi KABEYASAWA1, Koichi KUSUNOKI2, Daisuke KATO3,
Toshikatsu ICHINOSE4, and Akira TASAI5
1

Professor, Earthquake Research Institute, University of Tokyo, Tokyo, Japan,
kabe@eri.u-tokyo.ac.jp.
2
Professor, Department of Architecture, Yokohama National University, Yokohama, Japan,
kusunoki@arc.ynu.ac.jp.
3
Professor, Department of Architecture, Niigata University, Niigata, Japan,
dkato@niigata-u.ac.jp.
4Professor, Nagoya Institute of Technology, Nagoya, Japan,
ichinose@nit.ac.jp.
5Professor, Department of Architecture, Yokohama National University, Yokohama, Japan,
tasai@arc.ynu.ac.jp.

ABSTRACT: This paper reports on structural damages to reinforced concrete buildings
observed in Fukushima prefecture after the 2011 East Japan Earthquake. The survey was
conducted as part of reconnaissance activity of AIJ, Architectural Institute of Japan.
Typical severe damages to reinforced concrete school buildings are outlined, both by theground motions and the tsunami waves, based on the detailed field observation and withground motions recorded at K-net stations nearby. The causes of the damages are
discussed with problems peculiar to the buildings.
Key Words: damage survey, reinforced concrete, school buildings, damage evaluation,
ground motion, collapse

INTRODUCTION
Typical damages to reinforced concrete school buildings observed in Fukushima region, especiallyrelatively heavy damages such as collapse or near collapse, were reported here with the specificreasons in the structures. The survey was conducted as the reconnaissance activity of AIJ,
Architectural Institute of Japan, combined with the damage level evaluation requested from MEXT,
Ministry of Education. The details of investigation methods and the other results such as the damage
rates in the selected area will be analyzed and discussed elsewhere based on the statistical data of theinventory damage rates on the school buildings not only just with the ages of buildings but also on theeffects of retrofit or strengthening as well as in relation with calculated seismic performance indices.
Heavy and typical damages are reported below with the ground motions recorded at K-net stations
nearby (NIED, 2011).

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DAMAGES TO SCHOOLS IN NORTH FUKUSHIMA
K-net records at Fukushima city
The JMA intensity of the ground motion was defined as V+ at Fukushima city, but VI- at north
Fukushima, while the response spectrum was calculated as shown in Fig. 1 from the record at K-net
station of Fukushima (FKS003). The maximum acceleration response was close to 1G and the
maximum velocity response was close to 100kine, which may be regarded as close to or a little lessthan the very rare level, the level 2 of BSL.
Acceleration (m/sec/sec)

Velocity (m/sec)

FKS003 (福島)FKS003 (福島)

2

NS
EW
UD

9
8

1.6

7

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

2

NS
EW
UD

1.8

1.4

6

1.2

)
s/
m
(
v
S

5
4

0.8

3

0.6

2

0.4

1

0.2
0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0

5

Sv=100cm/sec

1

0

0.5

1

1.5

Period (sec.)
Period
(sec)

2

2.5

3

3.5

4

4.5

5

Period (sec.)
Period(sec)

Fig. 1 K-net records at Fukushima city
F-College in north Fukushima city
Collapse of a building, so-called pancake crush, was observed in F-college located north of Fukushima
city, which was three-story reinforced concrete building for administration built in 1965. The building
is located in the campus of the north area of Fukushima city, which is on a shallow hill with anadjacent drain on north end of the site. Relatively heavy damages were observed in the neighborhoodarea, which are now crowded with wooden houses, but were marshes in the old days.
The building had a Y-shaped plan with a stair hall in the center and three longitudinal blocks
spread to north, east and west directions as equivalent triangular as shown in Figure 3.2.3. The
foundation bases are PC piles with the depth of 6m. A continuous shear wall is located only at eachend of three blocks, while the walls along the stair in the center were not continuous and the otherwalls were non-structural partitions. The columns are located with 11m in the span and 5m in thelongitudinal direction, respectively.

Fig. 2 Second floor plan and south elevation of administration building in F-college

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The typical columns in the second story had the sectional size of 500x750mm, 12-D25+2-D16
main bars, the 9mm hoop bars set with the spacing of 250mm. The story height was 3800mm, though
the inner height of the columns in the longitudinal direction was 2000mm due to the spandrel walls, as
shown in an elevation in Figure 3.2.4, while the column inner height in the span direction was longer
up to 3000mm. Therefore, 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, because when one of the blocks is in the longitudinal, the others are mostly in span
directions, both skewed in thirty degrees, where the shear distribution ratios might have been relatively
smaller. The unequal shear distributions might have been one of the reasons why the severe collapse
was induced peculiar to this building.
As shown in the Photos 3.2.16 and 3.2.17, most of the slabs around the center stair hall in thethird floor had fallen down due to the shear and axial failure of columns in the second story, while thewalls at the ends could support the slabs though they inclined towards inside. Also as shown in Photos
3.2.18 and 3.2.19, the spandrel walls in the longitudinal direction could support the floor slabs so that
there are spaces enough to survive inside. As shown in Photo 3.2.20, the first-story did not collapse
probably owing to a wall in the center hall and amount of main bars increased in the first-story
columns. At the time of the earthquake, most of the college staffs working in the building could
evacuate before the collapse. It is estimated from the interview that the collapse might have occurredat the end of the main shock, probably around two minutes after they first felt the shaking. Three ofthem were confined but rescued several hours later so that no casualties were reported. A two-story
reinforced concrete building, attached nursery school, in the adjacent area suffered relatively severe
damage with axial compression at the column base. The other buildings in the college have been
constructed with the current code or retrofitted, which had no damages, slight or minor. The collapsedbuilding was the only one to be retrofitted in the near future.

Photo 1 South overviews of west wing and east wing

Photo 2 Collapse of the second story

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SCHOOLS IN MIDDLE FUKUSHIMA
K-net records at Koriyama city
The JMA intensity of the ground motion was defined as VI- at Koriyama city, while the response
spectrum was calculated as shown in Fig. 3 from the record at K-net station of Koriyama (FKS018).
The maximum acceleration response was close to 2.5G and the maximum velocity response was close
to 120kine, which may be regarded as exceeding the very rare level, the level 2 of BSL. The intensity
in the region might have been higher than in north Fukushima.
Acceleration (m/sec/sec)

Velocity (m/sec)
FKS018 (郡山)FKS018 (郡山)

2

25

NS
EW
UD

NS
EW
UD

1.8
1.6

20

1.4

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

2

1.2

15

)
s/
m
(
v
S

Sa=10m/sec/s10

Sv=100cm/sec

1
0.8
0.6
0.4

5

0.2

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0

5

0

0.5

1

1.5

Period (sec.)
Period
(sec)

2

2.5

3

3.5

4

4.5

5

Period (sec.)

Period (sec)Fig. 3 K-net records at Koriyama city
M-junior high school in Motomiya city
Motomiya city is in the middle area of Fukushima Prefecture where the JMA seismic intensity
recorded as V+. M-junior high school is located in a wide field area with a shallow hill rather close tonorth Koriyama. Therefore, the intensity might have been higher than V+ around the site. Figure 4
shows a plan view of the site with a section of the collapsed building. The school consists of two
reinforced concrete buildings, one steel gymnasium and one steel works. Photo 3(a) shows two
reinforced concrete buildings, both of which are 3-story buildings built in 1966. One building locatedin the south of the site, called south building, nearly collapsed and the other building located in thenorth, called north building, suffered heavy damage due to the earthquake.

Fig. 4 Plan view of M-junior high school
The south building has typical floor plan as school buildings in the age with five classrooms in afloor. The foundation bases are piles. The structure in the longitudinal direction is moment resisting1219

frame without shear walls. On the other hand continuous shear walls from base to top are located as
partitions between classrooms in the span direction except for two frames of the first floor. In otherwords the shear walls of these two frames are not continuous and isolated columns of the first floor
support all axial load generated by walls of upper floors, which could become very high during
earthquakes.
The columns are located only at the corners of each classroom with 9m in the longitudinal and7m in the span direction, respectively. The typical columns in the first floor have the sectional size of
750x500mm and 14-φ22 (longitudinal south frame) or 20-φ22 (longitudinal middle frame) main bars
(SR235). 9mm round hoop bars (SR235) with 90degree hooks are arranged for shear reinforcementwith the spacing of 250mm (column center) or 150mm (column end).
Photo 3(b) shows the southern view of the south building. As shown in the photo, the slabs
around the center of the building in the second floor had fallen due to the shear and axial failure ofcolumns of the first floor. These columns were isolated columns in the first floor supporting upper
shear walls. Therefore, the failure was supposed to be caused by very high axial load generated bywalls of upper floors. Photo 4 shows the damage of the isolated column located in the corridor side of
the classroom. Although the inner height of the column was long, the column suffered severe damage
showing crush of concrete and broken hoop reinforcement around the center of the column with hoop
spacing of 250mm. On the other hand, Photo 4 shows the damage of a side column of a barbell typeshear wall in the first floor. As shown in the photo the column failed in shear severely in thelongitudinal direction but the damage was light comparing to isolated columns due to the presence ofthe shear wall in the span direction. Photo 3(c) shows the damage of a column with a wing wall of thenorthern frame in the longitudinal direction. The inner height of the column was short due to the
spandrel walls and the column failed in shear severely. The damage grade of the south building may be
regarded as near collapse, while the grade of north building was rated as severe from the residual
seismic capacity ratio.

South building

North building

Photo 3 (a) South view of the buildings

Photo 3 (b) Collpase of south building(a) isolated column under walls (b) side column of barbell wall (c) column with sidewalls
Photo 4 Shear failure of columns in the first story1220

K-net records at Sukagawa city
The JMA intensity of the ground motion was defined as VI+ at Sukagawa city, while the response
spectrum was calculated as shown in Fig. 5 from the record at K-net station of Sukagawa (FKS017).
The maximum acceleration response was close to 2.5G and the maximum velocity response was close
to 160kine, which may be regarded as apparently exceeding the very rare level, the level 2 of BSL, inthe wide area up to 2 seconds. The intensity might have been higher in the region than in north
Fukushima or Koriyama, probably due to the soil amplification.
Acceleration (m/sec/sec)

Velocity (m/sec)

FKS017 (須賀川)

FKS017 (須賀川)

2

25

NS
EW
UD

NS
EW
UD

1.8
1.6

20

1.4

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

2

1.2

15

)
s/
m
(
v
S

Sa=10m/sec/sec10

Sv=100cm/s

1
0.8
0.6
0.4

5

0.2

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0

5

0

0.5

1

1.5

Period(sec.)
Period
(sec)

2

2.5

3

3.5

4

4.5

5

Period (sec.)
Period(sec)

Fig. 5 K-net records at Sukagawa city
S-elementary school in Sukagawa city
The appearance and the site plan of S-elementary school are shown in Photo 5 and Fig. 6. The school
consists of four RC buildings with three stories, all of which were built in 1965, which were connected
or isolated structurally using expansion joints. Among them, A- and B-buildings were severely
damaged. The JMA seismic intensity was VI+ at the station approximately 1 km east from the school.
The K-net station shown above was also close to the school. The damage to A-building is describedhere as an example.

B-Bldg
C-Bldg

D-Bldg
A-BldgSchoolyard

N

Pond

20m

80m
40m

Photo 5 An overview

Fig. 6 Site plan

The damage of the building was mainly observed in the longitudinal direction. The Is-values ofthe first and second stories in the longitudinal direction had been evaluated as 0.46 and 0.53,
respectively. The ultimate base shear coefficient (CTSD) was 0.47.

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In the first story of the building, the damages of the columns with wing-walls were serious asshown in Photo 6(a). These members failed in shear and vertically deformed, the damage rate of which
was Grade 5. The space of hoop reinforcements was approximately 300mm. In addition, about 70 % ofcolumns without wing-wall also failed in shear as shown in Photo 6(b). Damage levels of thesecolumns were between Grade 2 and Grade 4. The residual seismic capacity ratio was estimated to be
39% of the original capacity and the damage was graded as severe.

(a) column with wing-wall(b) column without wing-wall
Photo 6 Damage to columns in the first story

SCHOOLS IN SOUTH-EAST FUKUSHIMA
K-net records at Nakoso of Iwaki city
The JMA intensity of the ground motion was defined as VI- at Nakoso of Iwaki city, while the response
spectrum was calculated as shown in Fig. 7 from the record at K-net station of Nakoso (FKS012). The
maximum acceleration response was close to 1.1G and the maximum velocity response was close to
140kine, which may be regarded as close to the very rare level, the level 2 of BSL, though in the wide
frequency area up to 2.5 seconds. The spectral intensity in the region might have been not higher in the
short period region but higher in the longer period than the other areas, probably due to the site
amplification and also the directivity of waves to the site close to the source.
Acceleration (m/sec/sec)
11

Velocity (m/sec)

FKS012 (勿来)

10

NS
EW
UD

9

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

NS
EW
UD

1.8
1.6

8
2

FKS012 (勿来)2

Sa=10m/sec/sec

1.4

7

1.2

)
s/
m
(
v
S

6
5

Sv=100cm/sec

1
0.8

4
0.6
3
0.4
2
0.2

1
0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0

0

Period (sec.)
Period
(sec)

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Period (sec.)

Period (sec)Fig. 7 K-net records at Nakoso city
S-elementary school in Iwaki city
S-elementary school locates in the southern coast of Iwaki City, and the site is on the high plateau
locally. The place name of the site means tide watching hill. The investigated classroom building is areinforced concrete building of the west side part of the buildings shown in photo 7. The building is1222

connected to the east side building through an expansion joint. The investigated building with threestories and was constructed in 1974.
The first floor plan with the damage grade of structural members is shown in Figure 6.2.19. The
longitudinal direction of the building is composed of moment resisting frames including secondary
walls. In this direction, minor cracks of damage level I or II were observed in many columns and theirwing walls. The transversal direction of the building is rigid-frame structure with seismic walls of
100-120 mm in thickness. Diagonal cracks whose maximum damage level was level III were observedin the seismic walls at the first floor.

(a) South side view of the building(b) Shear cracks of a wall in span direction
Photo 7 An overview and damage of S-elementary school
I-high school in Iwaki city
Layout plan of the buildings in I high school is shown in Fig. 8. Buildings for classroom (Building A
and Building B) are located on the north and south. Two connecting corridor buildings (Building C
and Building D) are connected to Buildings A and B with expansion joint. Building A is four-story
reinforced concrete (RC) building, while Building B is three-story, and the Buildings C and D both
two-story for connecting corridor and classrooms. These were constructed from 1973 to 1975, portion
to portion over the years, as was typical process in the age.
The seismic intensity of JMA scale around the school was reportedly 5-. However, the school is
on a small hill with height of 30-40m from the plain land around, and all four buildings sufferedmoderate or severe damages. The damage level is much higher than another school buildings locatedjust at the foot of the hill. The amplification of the ground motions due to the hill zone effect isestimated from the damages though the quantity should be investigated further.
An overview of the Building A is shown in Photo 8. The north frame of the building was severely
damaged, and the columns of the special classroom at the west end of the building in the first floor
failed in shear up to the damage index of V. The vertical shortening of the columns was estimatedobviously from the deformation of the window frames between them as shown in Photo 9. On theother hand, the shear wall at the west end of the building suffered no serious damages as shown in
Photo 10. Some girders with standing wall in the north frame failed in shear. The floor level of
Building A was 15cm lower than that of Building C. The residual seismic capacity index was
calculated as R=33.3% for the longitudinal direction in the first story, by which the damage wasclassified into the severe damage.
Some of the columns in the Building B failed in shear, which were classified as the damage rateof IV as shown in Photo 11. The joint between Building B and D was damaged due to pounding. The
floor level of Building B was lower than that of Building D by 12cm. The residual seismic capacity
ratio was calculated as R=47% for the longitudinal direction of the first story. The damage wasclassified also into the severe damage.
Columns of the east frame in the first story of the Building C failed in shear evaluated as V withvertical shortening. The residual seismic capacity ratio R= 72% for the longitudinal direction of the1223

first story, by which the damage was classified into the moderate damage. In Building D, shear cracks
classified as III were observed in some columns, from which the residual seismic capacity ratio was
73% also classified into the moderate damage. The ground in front of the entrance subsided much.

Constructed at 1973
Constructed at 1974
Constructed at 1975

Gym.

Build. B

Build. D
En tranc e

Bu ild . C

Build. A

Gym.

Fig. 8 Location of buildings

Photo 8 An overview of the building A

Photo 9 Shear failure of the first story column at north frame of the building A

Photo 10 West side view of the building A

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Photo 11 Shear failure of the column
at the south frame of the building B

CONCLUSIONS
Typical structural damages to reinforced concrete school buildings observed in Fukushima prefecture
after the 2011 East Japan Earthquake were reported with design details of the buildings and also
ground motions recorded at K-net stations nearby. The survey was conducted as part of reconnaissanceactivity of AIJ, Architectural Institute of Japan. The causes of the damages are discussed with peculiar
problems to the buildings.

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 clericalsupports of the staffs in the local governments and MEXT and the technical support of practicalengineers on the field survey are gratefully acknowledged. The strong motion data at K-net stations
were downloaded from the web at NIED, National Research Institute for Earth Science and Disaster
Prevention.

REFERENCES
National Research Institute for Earth Science and Disaster Prevention(NIED, 2011):
http://www.k-net.bosai.go.jp/k-net/
JBDPA(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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