Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, JapanSTUDY OF LOW-RISE RC BUILDINGS WITHRELATIVELY HIGH SEISMIC CAPACITY DAMAGEDBY GREAT EAST JAPAN EARTHQUAKE 2011
Hamood AlWASHALI1 and Masaki MAEDA 2
1

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

ABSTRACT: This paper investigates the damage of several low-rise RC buildings
caused by the Great East Japan earthquake in Sendai city. The selected building areevaluated to have high seismic capacity, index Is > 0.7, using Japanese Standard for
Seismic Evaluation of Existing RC Buildings. Causes of the damage are discussed.
Moreover, pushover analysis was carried out to those buildings. In general, pushover
analysis predicted well the damage level, but there were some differences in plastic hinge
locations when compared to the actual damage.
Key Words: Great East Japan earthquake, seismic evaluation, existing RC buildings,
structural damage, pushover analysis.

INTRODUCTION
The Mw 9 Great East Japan Earthquake on the 11th of March 2011 had generated significant groundshaking in the western Pacific Ocean with its epicenter about 72 km east of the Oshika Peninsula of
Tohoku, Japan. The PGA exceeded 1000 gal in several locations and the maximum recorded
acceleration was 2699 gal in Miyagi prefecture obtained from National Research Institute for Earth
Science and Disaster Prevention (NIED) at station MYG004 N-S direction. Although RC buildings
preformed well and damage is not greater than previous earthquakes such as 1995 Kobe and 2004
Nigata Chuetsu Earthquake, some buildings with relatively high seismic capacity, Is index greater than0.7, were evaluated to have a moderate and severe damage.
.
This study presents the investigation of selected buildings which were evaluated to have relatively
high seismic capacity, but had moderate and severe damage induced by ground motion of the Great
East Japan Earthquake 2011.The selected buildings were chosen from Tohoku University`s post
earthquake damage survey and school investigation of reinforced concrete building structures
performed by RC committee of the Architectural Institute of Japan.
This paper is divided into two main sections. First the study of lecture-room RC building of
2-stories constructed in 1966 located in Tohoku University engineering campus which was severely
damaged is presented. This building will be referred to as N Lecture (Fig.1). N Lecture is compared toanother lecture-room building similar in its structural system and standing next to it but the latter was
slightly damaged. This building will be referred to as S Lecture.

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Secondly, the study of 3 storied RC building of an elementary school in Sendai city constructed in1974 is presented (Fig.2). 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 sidebuilding needed to be retrofitted and the West side was evaluated to have enough seismic capacity andno retrofitting was needed. The East side building, which had already seismically retrofitted suffered
only minor damage in its structural members. On the other hand, the West side building was heavily
damaged.

East

Fig. 1 N Lecture buildingWest

Fig. 2 North view of H school building
CASE STUDY NO.1

As mentioned above, two lecture-room buildings, N Lecture and S Lecture, were investigated andcompared. Both buildings are identical in plan, span, members’ sizes and reinforcement (see figure 3
and figure 4). Structural system in longitudinal direction is moment frame. However S Lecturebuilding have extra one shear wall in its longitudinal direction. The height of the 1st floor is also
different as shown in Fig.3 and Fig.4. Both buildings have nonstructural partial height concrete wall
attached against some of its columns. Therefore, the clear height of columns is also different from acolumn to another. Typical column size and its reinforcement is shown in Fig.5.
7 .3 m

7 .3m

3 .7m

7 .3 m

7 .4m

7.3m

3.7m

5.4m

5 .4m

9.2m

M

First floor plan

4.02m 3.93m

LPartial infill wall

M frameFig.3 N Lecture building plan and elevation
7.3m

7.3m

3.7m

7.3m

7.4m

9.2m

M

7.3m

3.7m

5.4m

5.4m

Extra shear wall

First floor plan

5.22m 3.93m

L

Extra shear wall

M frameFig.4 S Lecture building plan and elevation1293

500m m

700mm
700mm

1750mmColumn type1
Main bar: 20D22
Stirrups: Ø9@300mm

Column type 2
Main bar: 16D25
Stirrups: Ø9@300mm

Fig.5 Typical column size and reinforcement
Observed damage
The N Lecture building had a severe shear failure in many of its columns in the 1st story in thelongitudinal direction (see Fig.6). The damage to columns progressed much due to the 7th of April
aftershock earthquake (see Fig.7). Less damage in the 2nd story but shear cracks were also noticed.
First floor plan with damage classes of columns in the longitudinal direction are classified based on
the “Post-earthquake damage evaluation standards of Japan” (JBDPA 2001a) and shown in Fig 8. Twocolumns were damaged by previous earthquake and strengthened by FRB sheets jacketing are marked
as (未 unknown) in Fig. 8. It is marked unknown because damage to concrete was invisible by the
FRP jacket. The details of this repair were unavailable. However, the transverse direction was slightly
damaged.

Fig.7 After 7th of April aftershock earthquake

Fig.6 After 11th of March earthquake

Ⅰf
未

0

Ⅳs

Ⅲs

未

Ⅳs

Ⅲs Ⅱs

Ⅴs

Ⅱf

Ⅱ s ⅡsⅣsⅤsⅡs Ⅲ sⅤsⅡf

Ⅲs

0 : No cracks
I: slight damage. Cracks <0.2mm
II: Minor damage. Cracks 0.2mm~1mm.
III: Moderate damage. Cracks 1~2mm.
IV: Severe Damage.
V: Very Severe Damage.
未: unknown (repaired by FRB sheets.)
S : Shear damage.
f: Flexural damage.

Fig8. 1st floor plan and damaged observed in longitudinal direction For N lecture building

The S lecture building had slight damage. However, Small shear cracks from width of 0.2mm~1mm were noticed in the longitudinal shear wall. No cracks were seen in columns of 1st story.
Seismic evaluation results
The Japanese standard for Seismic Evaluation of Existing Reinforced Concrete Buildings (JBDPA

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2001b) was applied to the 1st story for the longitudinal direction of the both buildings and the results ofthe second level procedure are shown in Table 1. Is-Index is calculated by Eq.(1) .
(1)Is = E0 × S D × T

E0 is a basic structural index calculated by Eq.(2).

E0 = φ × 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 themode shape 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 the correlation
study from the past earthquake damage and the calculated indices for the damaged buildings. Past
experiences of the big earthquakes reported that buildings with Is-Indices higher than 0.6 escaped
severe damage or collapse.
Table 1 Seismic capacity in Second level procedure of 1st story longitudinal direction

Lecture N building

Lecture S buildingCF(groups) (groups)
0.16
1
0.46
1.14
0.35
1.9
0.37
1
0.32
1.23
0.29
2.5

E0

SD

CTU.SD

T

Is

0.86

0.975

0.72

0.9

0.755

0.9

0.95

0.76

0.9

0.77

Is index values for both building are about the same. Since Is> 0.7, both buildings were considered
to have sufficient seismic capacity and no retrofitting was needed.
Pushover analysis
Two-dimensional pushover analysis using computer program SNAP is carried out for the longitudinalframes. Beams and columns are idealized by two nonlinear rotational springs at their ends, nonlinear
shear spring in the middle and linear axial spring. A tri-linear relation is used for rotational and shear
springs. The stiffness after yielding is taken as 1/1000 of the elastic stiffness. Cracking and yield
moment of rotational spring and shear spring are estimated using AIJ standard (AIJ standard 1999).
The contribution of slab and hanging partial walls to the beams strength were ignored. The
beam-column connection is assumed to be rigid. The shearwall is modeled with an equivalent bracemodel suggested in (Aoyama 1987). The distribution of lateral forces in the pushover analysis isbased on the Ai distribution prescribed in the provision (Ministry of Land, Infrastructure and Transport
Notification 1980). The pushover analysis is carried till the story drift reaches the maximum story drift
which is assumed to be 1/100. The shear versus displacement relation of each story is reduced toequivalent single degree of freedom and expressed in spectral acceleration and displacement (Sa-Sd)
relations using procedures in Japanese performance-based seismic design (M. Midorikawa 2003).
Strong ground motion observation station of Tohoku University engineering campus (THU) is
located at distance of 250m from the investigated buildings as shown in Fig 9. The response spectra
for THU EW are plotted against pushover curves which represents the capacity of the buildings forboth buildings in Fig.10.

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N lecture
S lectureN

THU station

Fig. 9 Engineering campus of Tohoku University
The response spectra curve of THU EW has low values and sharp peaks at short periods as shown in
Fig.10 and intersects the capacity curve of both buildings at low Sa values. If the capacity method isused, the seismic response for both buildings was expected in the elastic region and that contradicts
the actual damage observed in the buildings. Therefore anticipated seismic response was chosen at the
point where the actual damage observed matched the damage calculated by pushover analysis which
was at relative story drift angle of about 1/200rad in the 1st story for both buildings. Due to large
spacing between stirrups, 300mm, brittle failure and rapid degradation of shear resistance is estimatedand shown as the green dotted line in Fig.8.

Spectral Acceleration, Sa（cm/s2）

THU EW with damped 5%
1200

THU EW with damped 10%1000

THU EW with damped 20%

800

N Lecture buillding Pushover
S Lecture building`s Pushover

600

expected Shear failure of columns
400

Anticipated earthquake response after
11th of March earthquake
expected brittle failure for N Lecture

200
0
0

2

4

6

8

10

12

14

Spectral Displacement, Sd (cm)Fig.10 THU EW response spectrum
Fig. 11 shows yielded hinge locations in frame in longitudinal direction of S lecture building atstory drift of 1/200rad. The Shear wall has yielded and hinges are formed in two beams and twocolumns. However, as for the actual damage for S Lecture building, only shear cracks was noticed at
the shear wall, no cracks was observed in other members. In the other hand, at the same story drift
angle, three columns of the N Lecture building had failed in shear (see Fig 12) and many columns
were about to fail in shear and had plastic hinges.
Plastic hinges were expected in some beams as shown in the Fig. 11 and Fig. 12 which were notnoticed in the actual damage investigation. This could be due to the contribution of slab which was notconsidered in the calculations of the beams strength capacity.
Flexural yield
Wall reached maximum shear capacity

M frameFig.11. Damage predicted using pushover analysis for S lecture at 1st story drift angle of 1/200rad1296Shear failure

Flexural yieldM frameFig.12 Damage predicted using pushover analysis for N lecture at 1st story drift angle of 1/200radComparison of base shear-displacement curve in the first story for both buildings between
pushover analysis results and seismic evaluation results is shown in Fig.13 and Fig.14. The F index isconverted to lateral displacement as follows: F=0.8 is equivalent to Inter-story drift of 1/500, F=1 isequivalent to Inter-story drift of 1/250, F=1.27 is equivalent to Inter-story drift of 1/150 and for F>1.27
the Eq.3 is used.
=.

−.( + .

(3))

Base shear coefficient

Where; Ry : Yield deformation in terms of inter-story, which in principle shall be taken as Ry = 1/150
and Rmu : Inter-story drift angle at the ultimate deformation capacity.
F=11First story Pushover

0.8

seismic evaluation results

0.6

shear failure

0.4

seismic response

0.2

SD cm

0
0

1

2

3

4

5

6

7

st

Base shear coefficient

Fig13. 1 story pushover and seismic evaluation results of N Lecture Building
F=1

1

First story pushover

0.8First Story seismic evaluation

0.6

Shear failure in column

0.4

Seismic response

0.2

SD cm

0
0

2

4

6

8

st

Fig14. 1 story pushover and seismic evaluation results of S Lecture Building

Discussion
When comparing damage predicted by pushover analysis with the observed damage, the pushover
analysis showed good estimation of the damage level and location of shear failure and plastic hinges.
As shown in Table.1 the Is index and CTU.SD index which represent the base shear for both of thebuildings are almost the same, but the N lecture building had a greater damage than expected in theseismic evaluation. This is thought to be of the poor construction of columns. The cover around the1297

stirrups is so thin in some cases 0.5 cm (see Fig.15). Moreover, the ends of bars should be hooked bybending through 180º in mild-steel bars and 135º in deformed bar. But in this case it was bent by angleof 900 as shown in Fig.16. Therefore, the bond between the concrete and stirrups is weak and thestirrups didn’t reach its maximum yielding point and slipped. The stirrups are not really helping shear
strength. The N Lecture building depends in its seismic capacity mainly on shear columns. In the other
hand, the S Lecture building depends mainly on the wall for its seismic capacity. The shear capacity
for the columns didn’t reach its maximum strength since most of the seismic load was carried by thewall which was not affected by the poor detailing of the stirrups.

Bent by 90o

0.5cm coverFig16. 90o hooks

Fig15. Cover of 0.5cm

CASE STUDY NO.2
3 storied RC building of an elementary school in Sendai city constructed in 1974 is studied. The
building is divided by expansion joint into building (A) and building (B) as shown in Fig. 17. Average
floor area for building (A) is 857.6m2 and total floor area of 2542 m2. Average floor area for building(B) is 1116m2 and total floor area of 3348 m2.
Building (B)

N

Ѳ≈45o

Exp. Joint
Building (A)Fig17. H elementary school
Seismic evaluation was carried out to both sides. According to the seismic evaluation, building (A)needed to be retrofitted and the building (B) was evaluated to have enough seismic capacity and no
retrofitting was needed. Building (A) was retrofitted by adding framed steel braces in the 1st and 2nd
floor and shear walls.
Observed damage
The longitudinal direction of building (B) had shear failure in many of its columns (see Fig.18) andshear cracks in some wing walls (see Fig.19). Cracks in slab and beams were also observed. The
transverse direction had slight damage. Damage was concentrated in the 1st floor of building (B).
As for building (A), minor damage was concentrated in 3rd floor. Flexural and shear Cracks of less1298

than 1mm in some columns in the 3rd story was noticed. As for 1st and 2nd floor, no damage wasnoticed. This could be because steel braces for retrofitting was only added to 1st and 2nd floors.

Fig18. Shear failure in column. Building (B)Fig.19 Shear Crack in side walls. Building (B)Typical story plan and its damage to the longitudinal direction of building (B) are shown in Fig. 20.
Typical member`s size and reinforcement is shown in Fig. 21.

X1

X2

X3

X4

X5

Ⅰ

X6

X7

X8

Ⅴ

Ⅳ

Ⅰ

X9

X10

Ⅰ

X11

X12

X13

X14

X15

X16

Ⅳ

Ⅲ

Ⅲ

Ⅲ

Ⅲ

Ⅰ

X17

X18

X19

X20

Ⅰ

Ⅱ

Ⅱ

Ⅱ

Y5

Ⅰ
Ⅰ

Ⅳ

Ⅲ

Ⅳ

Ⅳ

Ⅰ

Ⅰ

Ⅴ

Ⅴ

Ⅱ

Ⅱ

Ⅱ

Ⅱ

Ⅱ

Ⅳ

Y4
Y3
Ⅰ

Ⅱ

Ⅰ

Ⅰ

Ⅰ

Ⅰ

Ⅰ

Ⅰ

Ⅰ

Ⅰ

Ⅱ

Ⅱ

Ⅱ

Ⅱ

Ⅰ

Ⅰ

Ⅰ

Ⅱ

Ⅱ

Ⅰ

Ⅰ

Ⅱ

Ⅱ

Ⅰ

Ⅰ

Ⅰ

Ⅰ

Ⅰ

Ⅱ

Ⅰ

Ⅱ

Ⅱ

Ⅱ

Ⅱ

Ⅱ

Ⅰ

Ⅰ

Ⅰ

Ⅰ

Ⅰ

Ⅰ

Ⅰ

Y2
Y1

Fig. 20 1st floor plan and damaged observed in longitudinal direction of building (B)Typical column:
Main bar: 4D22, 8D19
Stirrups: Ø9@100mm

Typical beam:
Main bar: 2D22
Stirrups: Ø9@150mm

Fig. 21 Typical member size and reinforcement
Seismic evaluation results
The seismic evaluation for building (A) before it was retrofitted is shown in Table 2. Since Is index<0.7, which is the criteria in Japan, it was retrofitted. The seismic evaluation after retrofit for building(A) is shown in Table 3. The seismic evaluation after retrofit for building (B) is shown in Table4.

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Table 2 Second level screening 1st story longitudinal direction building (A) before retrofitC(groups)
0.21
0.44
0.02
0.04
0.07
0.14
0.01

F
(groups)
0.8
1
1.4
1.6
1.8
2.8
3.2

C

F

Eo

SD

T

CT.SD

Is

0.66

1

0.66

0.879

0.98

0.58

0.57

Table 3 Second level screening 1st story longitudinal direction building (A) after retrofitC(groups)
0.17
0.56
0.02
0.02
0.06
0.14
0.13
0.01

F
(groups)
0.8
1
1.4
1.6
1.8
2
2.8
3.2

C

F

Eo

SD

T

CT.SD

Is

0.88

1

0.87

0.879

0.98

0.77

0.75

Table 4 Second level screening 1st story longitudinal direction building (B)C(groups)
0.09
0.03
0.07
0.09
0.18
0.15
0.02

F
(groups)
0.8
1
1.75
2
2.25
2.6
3.2

C

F

Eo

SD

T

CT.SD

Is

0.50

1.75

0.87

0.93

0.98

0.461

0.80

Pushover analysis
Description of the pushover analysis as mentioned in previous section is used. The seismic response iscalculated using a bilinear idealization of pushover curves and procedures in Japanese
performance-based seismic design. Two Strong ground motion observation stations are located atsome distance from the school building. (See Fig. 22).
H School

N

JMA
Sendai

K-net
MYG013

Fig22. Strong motion observation stations

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The building is oriented at an angle of 45o from North (see Fig.17). The response acceleration atan angle of 45o form north will be referred as NW in this paper. Response spectra for NW of K-net
MYG013 (NIED) and NW of JMA Sendai (JMA) are plotted against pushover curve in Fig.23 andFig.24 respectively.
According to structural drawings, slits are inserted between columns and interior infill concrete
walls. However, these slits weren’t inserted properly. Columns which were assumed to have flexural
failure had actually failed in shear (see Fig. 18). Therefore, two cases are assumed for building (B);with slits and without slits.
2500

MYG013 NW damped h=5%Spectral sacceleration（cm/s2）

MYG013 NW damped h=10%
2000

MYG013 NW damped h=20%
Building (A) pushover
Case 1: Build(B) without slits

1500

Case 2: Build(B) with slits
Atincipated response by the earthquake

1000

shear failure in a column
500

0
0

2

4

6

8

10

12

14

Spectral displacement（cm）

Spectral accerleration （cm/s2）

Fig.23 MYG013 NW response spectrum and pushover curves

1400

JMA NW damped h=5%
JMA NW damped h=10%

1200

JMA NW damped h=20%
1000

Building (A) Pushover
800

Case 1: Pushover build (B) without slits
Case 2: Pushover build (B) with slits

600

Anticipated response by the earthquake
400

shear failure in a column

200
0
0

2

4

6

8

10

12

Spectral displacement cm
Fig. 24 JMA Sendai NW response spectrum and pushover curves

1301

14

Comparison between pushover analysis results for first story for both buildings and seismic
evaluation results is shown in Fig.25 and Fig.26
F=1Base shear coefficient

1

first story pushover
0.8

seismic evaluation after retrofit

0.6

seismic evaluation before retrofit

0.4

Seismic response (JMA)

0.2

SD cm

0
0

1

2

3

4

5

6

7

Base shear coefficientFig. 25 1st story pushover and seismic evaluation results building A
F=1

0.6

F=1.75Is index chosen at F=1.75
about 1.2% story drift

first story pushover

0.4

seismic evaluation
Shear failure in column

Shear failure ofshort columns

0.2

seismic response JMA

0
0

1

2

3

4

5

6

7

SD cm

Fig. 26 1st story pushover and seismic evaluation results building B
Discussion
Is index for both buildings are chosen at a ductility greater than F=0.8, which means that the failure of
extremely short columns was allowed in the seismic evaluation, since axial loads could be
redistributed to other columns and the building will not collapse. However, short column failed only inbuilding (B) and didn’t in building (A). This is due to several reasons; The CT.SD for 1st story at
ductility index F = 0.8 for building (A) is about twice of building (B), Table 5. It is thought thatbuilding (A) had a story drift just less than F=0.8. This is shown in Fig. 23 using anticipated seismic
response of JMA NW spectrum. Therefore short columns didn’t reach their maximum allowableductility and thus shear failure didn’t occur. In the other hand, The Is value for building (B) depends on
ductility (F=1.75) to reach the criteria of Is > 0.7. The anticipated seismic response using either JMA
NW or MYG013NW spectrum are greater than F=1 (see Fig.24). Therefore all short and shear
columns have collapsed.
Table 5 CT.SD at F=0.8
CT.SD at F=0.8
Building A

0.62

Building B

0.33

According to structural drawings, slits are inserted between columns and interior infill concrete
walls in building (B). However, these slits weren’t inserted properly. Therefore, columns that were1302

expected to have flexural failure, had shear failure. This resulted in greater damage than expected.
Two Response spectra, MYG013 KNET and JMA Sendai, are used for analysis. Using MYG013
response spectra, Fig. 21, it is demonstrated that more significant structural damage would occur inbuilding (A) and a higher probability of collapse for building (B).In the other hand, the damage
expected using JMA Sendai Spectra, Fig. 22, relatively matches the actual damage.
The actual damage for building B matches the pushover analysis results in some columns anddoesn’t in others columns. Some columns which actually failed in shear didn’t in the pushover
analysis. This is because plastic hinges were expected to occur in beams and not in columns, but thiswasn’t the case of the actual damage. This could be due to the contribution of the slab and thecontribution of hanging concrete walls to the beam`s strength.
The shear failure of short and shear columns in building (B) were expected in a major earthquake
using the seismic evaluation. This building wasn’t retrofitted since it’s judged that there is no threat tolife safety. However, the school could not use this building after the earthquake and repairing expenses
would be relatively high if compared to the retrofitting expenses for a better performance. If theschool administration was informed of possible consequences about the function of its building andrepairing costs after an earthquake, they might be willing to pay additional expenses for higher
performance. This case raises two issues; the function-ability of the building after the earthquake andthe lack of communication between the structural engineer and owner.

CONCLUSIONSThe pushover analysis predicted well the damage`s level and location in S and N buildings. In theother hand, for H school building there were some differences in damage locations. Plastic hinges
were expected to occur in beams and not in columns, but this wasn’t the case in the actual damage. In
general, capacity spectrum method predicted well the level of damage in the H school building.
As for the lecture room buildings in Tohoku University, it is concluded that the main cause forgreater damage than expected by the seismic evaluation method was because of the poor construction
observed in detailing the columns. As for the H school building, the shear failure of short and shear
columns in building (B) were expected in a major earthquake using the seismic evaluation. The slits
weren’t inserted properly. This resulted in greater damage than expected. This case raises the problemof the function-ability of the building after earthquakes.

REFERENCES
AIJ (1999) standard for structural calculations of reinforced concrete structure .(in Japanese)
Aoyama, H. and Uemura, T. (1987) “Structural analysis using matrix method” Baifucan Co.,1987,
pp.174-190 (in Japanese)
JBDPA. (2001a). “Standard for Post-earthquake Damage Level Classification of Reinforced Concrete
Building”.
JBDPA. (2001b). “Standard for Seismic Evaluation of Existing Reinforced Concrete Buildings”.
JMA, http://www.seisvol.kishou.go.jp
Ministry of Land, Infrastructure and Transport Notification. “Technical Standard for Calculation ofSeismic Story Shear Distribution Factor along the Height of a Building Structure, etc”.
No.1793-1980, 1980. (in Japanese).
M. Midorikawa, I. et al, (2003) “Performance-based seismic design code for buildings in Japan”
Earthquake Engineering and Engineering Seismology.
NIED K-NET, http://www.k-net.bosai.go.jp/k-net/

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