Paper No. M-3

PERFORMANCE OF HIGH-RISE BUILDINGS AND SEISMICALLY ISOLATEDBUILDINGS AT THE 2011 GREAT EAST JAPAN EARTHQUAKETaiki SAITO1, Izuru OKAWA1 and Toshihide KASHIMA1SUMMARY
Building Research Institute (BRI) has been conducting strong motion observation for buildings
since 1957. At the 2011 Great East Japan Earthquake on March 11, 2011, strong motion records
were collected at 54 stations in Japan. From the observed records, it was found that the high-risebuildings shook largely because of the effect of long period component of earthquake groundmotions. Also, from the site investigation, seismically isolated buildings showed excellent
performance without any severe damage even to nonstructural elements in superstructure. However,some damage to isolation dampers and expansion joints were observed. This paper summarizes theperformance of high-rise buildings and seismically isolated buildings during the earthquake.

INTRODUCTION
Building Research Institute (BRI) has been
conducting strong motion observation forbuildings since 1957. At the 2011 Great East
Japan Earthquake on March 11, 2011, strong
motion records were collected at 54 stations
located from Hokkaido to Kansai area in Japan
shown in Figure 1.

asSendai

From the records, it was found that the highrise buildings shook largely because of theeffect of long period component of earthquake
ground motions. Especially, a high-risebuilding in the city of Osaka, 770 km awayfrom epicenter, experienced large shaking inexcess of 1.5 m amplitude at the top floor.
This phenomenon is considered due to theimpact of long-period earthquake groundmotion.

TokyoOsaka

Figure 1. Location of stations
1 Building Research Institiute, Email: tsaito@kenken.go.jp, okawa@kenken.go.jp, kashima@kenken.go.jp

After the 2011 Great East Japan Earthquake, an investigation team consisted by the members fromNILIM (National Institute of Land, Infrastructure and Management) and BRI (Building ResearchInstitute) was dispatched to the disaster areas on July 1st and 2nd to examine performance of SIbuildings. The seismically isolated buildings showed excellent performance without any severe
damage even to nonstructural elements in superstructure. However, some damage to isolation
dampers and expansion joints were observed. This paper introduces some cases to explain seismic
performance of seismically isolated buildings.

PERFORMANCE OF HIGH-RISE BUILDINGS
Input ground motion and response of high-rise buildings
Table 1 shows the list of high-rise buildings under observation located in Sendai, Tokyo and Osakaand the maximum acceleration values observed in the buildings. Figure 2 shows the velocity
response spectra of the horizontal records at the lowest levels of the high-rise buildings in Miyagi,
Tokyo and Osaka. The velocity spectra of Miyagi and Tokyo have strong component in the wideband period from 0.5 seconds to 10 seconds; therefore, it is considered not only high-rise buildings
but also low-rise buildings were strongly shaken by the earthquake ground motions. On the otherhand, the response spectrum of Osaka has a peak period of 6-7 seconds, and it was a typical longperiod ground motion which shakes high-rise buildings.
Table 1. List of high-rise buildings and observed acceleration records
Location

Structural
Type

Structuralsystem

Floor∆ (km)

Locationof Sensors

ASendaiS

Normal

B2F
15F

175

B

TokyoRC

Normal37F

385

COsakaS

Normal

52F
P3F

770

B2F
15F01F18F
37F
01F
18F
38F
52FN
52FS(cm/sec)
1005% visous damping
Building A(Miyagi)

10Building B(Tokyo)
Building C(Osaka)

10Acc. (cm/s2)
H1H2V
163
259
147
361
346
543
87
98
41
118
141
64
162
198
108
35
33
80
41
38
61
85
57
18127
88
13129
85
12(sec)0

1

Figure 2. Velocity response spectra10Figure 3 shows the displacement records observed in different floors of high-rise buildings inTokyo and Osaka. Whereas the maximum displacement at the top floor of Building B in Tokyo, 385
km away from the epicentre, was 24 cm, the large floor movement of 136 cm amplitude wasobserved at the 52nd floor of Building C in Osaka, 770 km away from the epicentre. By this shaking,in Building E, all 32 lifts stopped and people were trapped in four of them. Damage to nonstructural members such as falling of gypsum board and ceiling panels were observed extensively.
30cm

150cm

01F

1F
00max. disp = 9 cm

-30
30max. disp = 7 cm

-150cm

150cm
18F

18F
00max. disp = 16 cm-3030max. disp = 29 cm-150cm

150cm

37F

38F

00max. disp = 24 cm-300100200300

400500(b) Building B (Tokyo)

sec
600max. disp = 85 cm

-150
150cm
52F0max. disp = 136 cm-1500100

sec
200300400500600(a) Building C (Osaka)

Figure 3. Displacement records of high-rise buildings in Tokyo and Osaka
Figure 4 shows the Fourier spectra of acceleration records observed at 1st , 18th and 37th floor of thehigh-rise building B in Tokyo. The spectra of the records at 18th and 37th floors have two peaks
which correspond to the first and second mode vibrations. Minor damage around the entrance ofeach residential unit was observed as shown in Figure 5. The number of units which suffereddamage was counted in each floor and it is seen that the damage distributes in the medium floors.
This fact suggests the effect of second mode vibration.
Floor
3530
2520
15
105unit

00Figure 4. Fourier spectrum (Building B)

51015Figure 5. Damage distribution in each floorVibration characteristics of high-rise buildings
Using strong motion records observed at the main shock of the 2011 Great East Japan Earthquake,the vibration characteristics of high-rise buildings were identified. The N4SID (Numericalalgorithm for Subspace based State-Space System Identification) method was used for this analysis.
1)Vibration characteristics of steel high-rise building (Building A)
Building A is a 17-story steel building built in Miyagi Prefecture, and seismic dampers are notinstalled in the building. To split every 30 seconds of the observation record, natural frequency anddamping factor were identified for every interval. Figure 6-(a) shows the results of identification. It
can be seen that the first and second natural frequencies do not change very much during theearthquake. The first mode damping factor slightly increases up to 3% when ground motion
becomes large and then reduces to 2%. A similar trend was also observed in other steel high-risebuildings. Damage of structural members has not been reported in any building.
2)Vibration characteristics of reinforced concrete high-rise building (Building B)
Building B is a 37-story reinforced concrete building built in Tokyo, and seismic dampers are notinstalled in the building. Figure 6-(b) shows the results of identification. The first natural frequency
has declined about 25% compared to the initial value during the earthquake. The first mode
damping factor increases up to 6% after ground motion becomes large. This change is considered tobe due to crack of structural element occurred at the main shock.

(a) Steel (Building A, H1 direction)(b) Reinforced concrete (Building E, H1 direction)

Figure 6. Change of vibration characteristics of high-rise buildings during the earthquakePERFORMANCE OF SEISMICALLY ISOLATED BUILDINGS
Reflecting high consciousness of earthquake risks in Miyagi Prefecture and nearby areas in Tohoku
region, Japan, there are many seismically isolated buildings (hereinafter referred to as SI buildings)
have been constructed in those areas. Table 2 shows the list of SI buildings investigated by NILIM
and BRI. The list contains the JMA (Japan Meteorological Agency) seismic intensity (from 0 to 7)
near the building. Most buildings in the list suffered severe ground motion with the intensity morethan 6 minus.
Table 2. List of SI buildings investigated on July 2nd and 3rd in 2011
Usage

DEFGH
IJKL
M
NO

OfficeWarehouse
Condominium
Condominium
Condominium
Condominium
Hospital
OfficeHotelFirehouse
HospitalFirehouse

Structural typeand number offloors
SRC, 9F+B2F
S, 1F
RC, 14F
RC, 12F
RC, 15FRC, 10FRC, 6FRC, 18F +B2F
RC,12F
S, 3F
RC, 5FRC, 3F

P
Q

HospitalFirehouse

S, 6F
RC, 3F

RS
T

Hospital
Hospital
Hospital

Existence ofscratch board○○

Existence ofearthquake
record○○○○○○○JMA Seismic
Intensity near
the building6 minus
6 minus
6 minus
6 minus
6 minus
6 minus
6 minus
6 minus
6 plus6 plus6 plus6 minus – 6 plus
5 plus

5 plus - 6 minusRC, 4F
6 minusRC, 10F○4SRC, 4F○
5 plus(SRC: steel reinforced concrete, RC: reinforced concrete, S: steel)

Summary of investigation
Investigation results of 16 SI buildings in Miyagi-Prefecture and one SI building in YamagataPrefecture is summarized as follows:a) Super-structures of SI buildings suffered almost no damage even under strong shaking with
JMA intensity 6 plus. It verifies the excellent performance of SI buildings.
b) In some buildings, damage was observed at the expansion joints. It seems that parts ofexpansion joints were not well operated due to the large displacement of SI floor during
earthquake (Figure 7).
c) Subsidence of ground around the building was observed in some buildings.
d) Many cracks were found in lead dampers. These cracks might be increased by the aftershocks(Figure 8).
e) Peeling off of paint was observed widely for U-shape steel dampers. In some cases, residual
deformation of steel was remained (Figure 9).

Figure 7. Damage at the expansion joints

Figure 8. Cracks in lead dampers

Figure 9. Peeling off of paint of steel dampers

Records of seismically isolated buildings
There are 8 buildings with scratch boards to measure displacement of the SI floor. As shown in
Figure 10, in most cases, the maximum displacement has been estimated around 20 cm. There is a
one case with the maximum displacement estimated over 40 cm. For two buildings, there areaccelerometers in the building and the observed maximum accelerations are listed in Table 3.
Around 40-60% reduction was achieved by SI system.

(a) Around 18cm (Building D)(b) Around 21cm (Building E)(c) Around 21cm (Building J)(d) Around 40cm (Building O)(e) Around 25cm (Building P)(f) Around 25cm (Building Q)

Figure 10. Maximum displacement from the scratch boards
Table 3. Maximum acceleration observed below and above the isolation floor
Building B

Below SI floor
Above SI floor

Building K

X direction

Y direction

X direction

Y direction

250.8 (100.0)

289.0 (100.0)

310.8 (100.0)

225.8 (100.0)

143.7 ( 57.3)
120.5 ( 41.7)
173.0 ( 55.7)
142.9 ( 63.3)
Unit: gal ( the percentage of reduction by SI is shown in the blancket )CONCLUSIONSAt the 2011 Great East Japan Earthquake, high-rise buildings in a wide area of Japan were shaking
largely and damage occurred to non-structural members. Especially, a high-rise building in the cityof Osaka, 770 km away from epicenter, experienced large shaking in excess of 1.5 m amplitude at
the top floor. This phenomenon is considered due to the impact of long-period earthquake groundmotion. From the acceleration records observed in a building, it was found out that the natural
frequency and the damping factor varied during the earthquake. Especially, in case of reinforced
concrete high-rise buildings, the first natural frequency declined about 20% and the damping factor
increased 2-4% after the earthquake, probably due to the influence of crack of structural members
occurred at the earthquake.
Seismically isolated buildings showed excellent performance without any severe damage even to
nonstructural elements in superstructure. However, some damage to isolation dampers andexpansion joints were observed.

REFERENCES
1. National Institute for Land and Infrastructure Management (NILIM) and Building ResearchInstitute (BRI) , Summary of the Field Survey and Research on "The 2011 off the Pacific coastof Tohoku Earthquake" (the Great East Japan Earthquake), September, 2011,
http://www.kenken.go.jp/english/contents/topics/20110311/0311summaryreport.html.