Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, JapanBEHAVIOR OF A BASE-ISOLATED BUILDING AT
FUKUSHIMA DAI-ICHI NUCLEAR POWER PLANT
DURING THE GREAT EAST JAPAN EARTHQUAKE
Katsuichirou HIJIKATA1, Makoto TAKAHASHI2 , Takayuki AOYAGI3and Mitsugu MASHIMO4
1 General Manager, Nuclear Seismic Engineering Center, Nuclear Asset Management Department,

Tokyo Electric Power Company, Tokyo, Japan
2 Architectural Engineering Group, Nuclear Asset Management Department,

Tokyo Electric Power Company, Tokyo, JapanManager, Architectural and Structural Engineering Operation Center,Tokyo Electric Power Services Co., Ltd, Tokyo, Japan
4Manager, Architectural Nuclear Power Department, Tokyo Electric Power Services Co., Ltd,Tokyo, Japan
3ABSTRACT: Based on the experience of the Niigataken Chuetsu-oki Earthquake in2007 at Kashiwazaki-Kariwa Nuclear Power Plant (NPP), TEPCO constructed thebuildings equipped with seismic base-isolation system, which houses emergency
response centers for each Nuclear Power Plant, including Fukushima Dai-Ichi NPP.
Although strong ground motion was observed at Fukushima Dai-Ichi NPP in the Great
East Japan Earthquake in 2011, the base-isolated building was not damaged. This paper
shows behavior of the building during the earthquake using observation records.
Key Words: Great East Japan Earthquake, Fukushima Dai-Ichi NPP, Base-isolatedbuilding, Observation records, Simulation analysis

INTRODUCTION
The Niigataken Chuetsu-oki Earthquake (M6.8) occurred on July 16, 2007. Though the strong groundmotion that was 6+ by JMA intensity measure was observed at TEPCO Kashiwazaki-Kariwa NPP site,
reactors were shut down safely and no damage to the safety of NPP facilities occurred.
According to the requirement to provide “Emergency Headquarter” in NPP site, there is one
located at Kashiwazaki-Kariwa NPP site on the first floor of the office building. The main shock of theNiigataken Chuetsu-oki Earthquake gave little structural damage so that the “Emergency Headquarter”
remained safe. However, some damage such as the falling down of ceilings, failure of locks of doors,
turning over of racks, trouble of sanitary system and so on, brought the loss of the functions to carryout the emergency response (TEPCO,2007).
Following the fact above, TEPCO has planned to provide “Base-isolated Important Building” thatpossesses the function as “Emergency Headquarter” to every NPP site, so one of the buildings wasconstructed at Fukushima Dai-Ichi NPP site in March, 2010.

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OUTLINE OF THE BASE-ISOLATED IMPORTANT BUILDING

40.6 mThe exterior and the outline of the building are shown in Picture 1 and in Table 1, respectively.
Base-isolation system consists of 4 Laminated rubber bearings (LRBs) at corners, 10 Natural rubberbearings (NRBs) at perimeter, 31 sliding bearings and 16 oil dampers. Sliding bearings are employed
to obtain longer natural period since the 2 story building brings relatively small axial force on eachbearing. Oil dampers are provided to avoid excessive displacement. Figure 1 shows the arrangement ofbase-isolation devices.
For the Base-isolated Important Building at Fukushima Dai-Ichi NPP, 7 input motions areemployed as design ground motion, 3 spectrum compatible artificial ground motions (1.5 times
specified by Building Law), 3 standard observation records, 1 Design Basis Ground Motion (780 Gal
at base) used for the seismic design of reactor facilities.

NPicture 1 Exterior of the Base-isolated
Important Building
Table 1 Outline of the Base-isolated Important
Building
Place
Completion
Use
Building Area
Total Floor Area
Number of Floor
Building height
Structure Type52.6 mMark

Okuma-machi, Futaba-gun,
Fukushima Prefecture
March, 2010
Emergency Headquarter
1,815 m2
3,600 m2
2 Floors
11.95 m
SRC with S

DeviceLaminated rubber bearing (LRB)

Diameter ：φ1200mm (rubber)Thickness ：H=240mm
Diameter ：φ240mm (lead plug)

Numbers4

Natural rubber bearing (NRB)
Diameter ：φ1200mm
Thickness ：H=240mm10Sliding bearing

31

Oil damper

16Fig. 1 Arrangement of base-isolation devices

EARTHQUAKE OBSERVATION
In order to examine the performance of base-isolation, seismic motions are recorded by seismometer
installed at the basement pit, the first floor and the second floor of Base-isolated Important Building inFukushima Dai-Ichi NPP site. Observation in the ground is also carried out in northern part of the site.
Figure 2 shows the arrangement of the observation points.
20 days after start of observation on February 21, 2011, the Great East Japan Earthquake (Mj9.0)
occurred on March 11, 2011. Though the main shock and after shocks were recorded on that day, datacollection was completed about 2 months after since data collection was disturbed by some accident
such as hydrogen explosion.
Figures 3 to 5 show the time histories of accelerations. Figure 6 shows the pseudo velocity
response spectra. From these figures it can be seen that horizontal responses at the first floor and thesecond floor are remarkably reduced comparing with that at the basement pit, especially in the period
range of 2 second and shorter. On the other hand, the vertical responses at the first floor and thesecond floor are slightly larger than that at the basement pit.

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Seismometer
UD
Vertical Array
Observation Point

EW
NS

Base-isolated Important Building
G.L.+4.30 m

2nd Floor

G.L.+0.45 m

1st Floor

G.L.-3.10 m

Basement Pit(b) Building section(a) Vertical array observation point(d) First floor(c) Basement pit(e) Second floor

155

400

Acc.(Gal)

Acc.(Gal)

Fig. 2 Observation points

200
0-200-400
4060

80100120

1401601802000-200-400
40200

185

400

60

176400200
0-200-4004060

80100120140160

180Acc.(Gal)

Acc.(Gal)

0-400
80

100

120140160

180Acc.(Gal)

Acc.(Gal)

0-400
80

100

120

140

200

160

180200160

180200160

180

200

06080

100

120

140756

800
400
0-400
6080

100120140Time (sec)Timepit(sec)(c) Basement

570

60

180

-200

-800
40200

400

-800
40160

213

Time (sec)Timepit(sec)(c) Basement
800

140

Time (sec)Time (sec)(b) First floor

582

60

120

200

-400
40200

400

-800
40

100

400

Time (sec)Time (sec)(b) First floor
800

80Time (sec)(sec)(a) Second TimefloorAcc.(Gal)

Acc.(Gal)

Time (sec)(sec)(a) Second Timefloor

160

180

400
0-400
-800
40200

699

800

60

80

100120140Time (sec)(sec)(d) GroundTimesurfaceTime (sec)(sec)(d) GroundTimesurfaceFig. 3 Time histories of acceleration (NS)Fig. 4 Time histories of acceleration (EW)

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400
0-400
140

160

180200

500

400

10200
100

120

140

160

1805050

446

800

速pSv
20度(cm/s)

4000(cm/s)

-400
-800
40

60

80

100

120

140

160

180

2000.
1105Time (sec)Timepit(sec)(c) Basement

0.
01

2nd Floor
1st Floor
PitGround2239

800

100100200400

10-4000.50.02
6080

100120140160

1800.05

0.12005005101100100

50

50
速pSv
20度(cm/s)(cm/s)10(h=0.05)

50

100

2200

1002001(cm)(h=0.05)200(cm/s2)
50
01

1000

102000(cm)

0.5(a) NS

Fig. 5 Time histories of acceleration (UD)500

0.2Period(sec)
周 期(秒)

Time (sec)(sec)(d) GroundTimesurface(cm/s2)-800
4020080

50060Time (sec)Time (sec)(b) First floorAcc.(Gal)(h=0.05)-400-800
40Acc.(Gal)101000Acc.(Gal)

(cm)

516

800

200120Time (sec)(sec)(a) Second Timefloor

50
0100(cm/s2)

80

1000

60

2000

-800
402000Acc.(Gal)

621

800

50
0.
1

速pSv
20度
(cm/s)

10(cm/s)

50.
1

105

0.
01

10.5
0.02

0.
01

2nd Floor
1st Floor
Pit
Ground

2

0.05

0.1

0.2

0.5

1

25

2nd Floor
1st Floor
Pit
Ground

2
1
10

0.5
0.02

0.05

0.1

0.2

0.5

1

Period(sec)
周 期(秒)

Period(sec)
周 期(秒)(b) EW(c) UDFig. 6 Pseudo velocity response spectra

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From Fig. 7 showing the ratios of responses to that at basement pit, it can be seen that horizontalresponses are reduced by 30% in the shorter period range and the vertical responses increase at 0.03
sec. for first floor and at 0.08 sec. for second floor, respectively.
In order to examine oscillation characteristics, band-passed motions corresponding to the 0.3 sec.
which is the natural period showing very small spectral ratio for horizontal motion, and 0.03 sec. and0.08 sec. which are the natural periods showing very large spectral ratio for vertical motion arecalculated followed by acceleration distributions shown in Fig. 8. In this figure, acceleration
distributions from 0 to 250 sec. are drawn for each time step of 0.01 sec.
Figure 8 shows that base-isolation can decrease the horizontal responses of the upper structure,and that 0.03 sec. corresponds to the vertical first mode of base-isolation and upper structure system
and 0.08 sec. corresponds to the vertical first mode of the upper structure itself.
Figure 9 shows the orbit of relative displacement between the first floor ant the basement pit
obtained by integrating the acceleration records. In the horizontal plane, large displacement of about
20cm is obtained in E-W direction, and a very small displacement of 1 cm is obtained in the verticalplane.
4Spectrum Ratio

2nd Floor／Pit
1st Floor／Pitス
ペクトル
比3(a) NS
20.3 sec
100.02

0.05

0.1

0.2

0.5

12

5

10Period(sec)
周 期(秒)
4

Spectrum Ratio

2nd Floor／Pit
1st Floor／Pitス
ペクトル
比3(b) EW20.3 sec
100.02

0.05

0.1

0.2

0.5

12510Period(sec)
周 期(秒)
4Spectrum Ratio

0.03 sec
スペクトル
比0.08 sec(c) UD3

2nd Floor／Pit
1st Floor／Pit

2

10
0.02

0.05

0.1

0.2

0.5

1

2

510Period(sec)
周 期(秒)

Fig. 7 Response spectrum ratio of the floor vs basement pit

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GL(m)

GL(m)

GL(m)

GL(m)

5

5552FL 442FL 443333222211

101FL 01

0-1-1-1-1-2-2-2-2-3-3-3-31FL

Pit-4-600-300

0300

Pit-4-600

600-3000300-4-600600

加速度(Gal) (Gal)
Acceleration

加速度(Gal) (Gal)
Acceleration

0-3000300

600-4-600-300

0300

600

加速度(Gal) (Gal)
Acceleration

加速度(Gal) (Gal)
Acceleration(a) NS(b) EW(c) UD(d) UDaround 0.3 sec.(2～4Hz)

around 0.3 sec.(2～4Hz)

around 0.03 sec.(20～50Hz)

around 0.08 sec.(10～15Hz)

Fig. 8 Acceleration distribution of band-passed wave
30

202010100UD 0(cm)-10-10-20-20-30-30NSNSNS(cm)30-20-1001020-30-3030-20-100102030EWEW(cm)EWEW(cm)

Fig. 9 Orbit of relative displacement between first floor ant basement pit

SIMULATION ANALYSIS
Simulation of observed record was carried out with the oscillation model employed in the design ofBase-isolated Important Building. The upper structure was modeled as lumped-mass model with 3masses as shown in Fig. 10. Specifications of the model are summarized in Table 2. Specifications ofNRB, LRB, sliding bearing and oil damper in the base-isolation system are summarized in Table 3.
NRB is a linear spring, but other devices are modeled by non-linear spring as shown in Fig. 11.
Observation record at basement pit was employed as input motion, and input revel was set asshown in Fig. 10. Comparisons of simulated peak acceleration and observed peak acceleration at eachfloor are shown in Fig. 12. Figures 13 and 14 show the comparison of the simulated time histories andobserved ones.
Though simulated peak accelerations are slightly smaller than observed ones, there is a good
agreement between time histories. Also there is a good agreement between the acceleration response
spectra as shown in Figs. 15 and 16. Figure 17 shows the comparison of orbit of relative displacement,
which are obtained by integrating acceleration time history. It can be seen that simulated relative
displacement agree with observed one.

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From the above comparison, it is concluded that oscillation model used in the seismic design cansimulate the real phenomena very well and that the design of the Base-isolated Important Building
was conducted properly.

RFL

Table 2 Specifications of oscillation model

4.44m
2FL
4.49m
1FL

Floor

Height(m)Weight(kN)

RFL2FL
1FL

4.44
4.49

23,70018,60042,600Total-

84,900

Horizontal stiffness (kN/m)
NS direction EW direction
1.660 x107
1.191 x107
1.827 x107
2.136 x107--Input motion

Fig. 10 Oscillation model

Table 3(a)Specifications of NRB

Shear modulus
Gr (N/mm2）

Total section area
Ar (cm2)

Total thicknessd (cm)

0.294

113,048

24

Table 3(b)Table 3(c) Specifications of sliding bearing
Total verticalFriction
force
coefficientN(kN)
μ60,4170.013

Frictionforce
μN(kN)
785.4

Specifications of LRB

Total section Total sectionTotal
Shear modulus areaofrubber
areaoflead
plug
thickness2
Gr (N/mm ）Ar (cm2)
Ap(cm2)d (cm)
0.392
43,4291,810
24

Table 3(d) Specifications of oil damper

Horizontal
stiffness
K(kN/m)
3.93×105

Damping Damping Relief Relief
coefficient coefficient force
load
C1
C2
velocity(kN/kine) (kN/kine) Fr(kN) Vr(m/s)
25.0
1.70
800
0.32

Max.
Max.
load velocity
Fmax Vmax
(kN)
(m/s)
1,000
1.50

FFmax
C2FrC1(a) LRB(b) sliding bearing(c) oil damper

Fig. 11 Nonlinear hysteresis characteristics of devices

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VFL

FL

RR

Obs.
観測記録
Cal.
解析結果

Obs.
観測記録
Cal.
解析結果

22

11Pit
GND

Pit
GND
0200

400

600

800 1000

0200

400

Acc(cm/s 2)

600

800 1000

Acc(cm/s 2)(a) NS(b) EW

155

250
125

Acc.(Gal)

Acc.(Gal)

Fig. 12 Comparison of simulated peak acceleration and observed one
Obs.

0-125-250
4060

80

100

120

140160

180

125

Obs.

0-125-250
40200

176

250

60

80

100

118

250
125Cal.

0-125-250
4060

80

100

120

140120140160180200160

180200160180200160180200Time (sec)Time (sec)Acc.(Gal)

Acc.(Gal)

Time (sec)Time (sec)

160

180

125

Cal.

0-125-250
40200

127

25060

80

100

Time (sec)Time (sec)

120

140

Time (sec)Time (sec)(a) Second floor(b) First floor

185

250
125Acc.(Gal)

Acc.(Gal)

Fig. 13 Comparison of simulated time histories and observed one (NS)Obs.

0-125-250
40

60

80

100

120

140

160

180

125

Obs.

0-125-250
40

200

213

250

60

80

100

157

250
125

Cal.

0-125-250
4060

80

100

120

140120140Time (sec)Time (sec)Acc.(Gal)

Acc.(Gal)

Time (sec)Time (sec)160180125

Time (sec)Time (sec)Cal.

0-125-250
40200

162

2506080100120140

Time (sec)Time (sec)(a) Second floor(b) First floor

Fig. 14 Comparison of simulated time histories and observed one (EW)1549

(h=0.05)

3000

Obs.(2FL)
Cal.(2FL)
Obs.(Pit)

速2000
1500
1000

2000
1500
1000
500

500
00.02

Obs.(1FL)
Cal.(1FL)
Obs.(Pit)

2500

Acc.(Gal)

Acc.(Gal)2500(h=0.05)

3000

0.05

0.1

0.2

0.5

1

2

5

00.02

10

0.05

0.1

0.2

0.5

12510

Period (sec)Period (sec)(a) Second floor(b) First floor

Fig. 15 Comparison of acceleration response spectra (NS)(h=0.05)

3000

Acc.(Gal)

速1500
1000

2000
1500
1000
500

500
00.02

Obs.(1FL)
Cal.(1FL)
Obs.(Pit)

2500

2000

0.05

0.1

0.2

0.5

12500.02

100.05

0.1

0.2

0.5

(a) Second floor(b) First floor

Fig. 16 Comparison of acceleration response spectra (EW)

30
Obs.
Cal.

20
100-10-20-30-30

1Period (sec)Period (sec)NS (cm)Acc.(Gal)2500(h=0.05)

3000

Obs.(2FL)
Cal.(2FL)
Obs.(Pit)-20-100102030

EW (cm)Fig. 17 Comparison of orbit of relative displacement

15502510

CONCLUSION
Based on the experience of the Niigataken Chuetsu-oki Earthquake in 2007 at Kashiwazaki-Kariwa
NPP site, the Base-isolated Important Building for emergency response was constructed in Fukushima
Dai-Ichi NPP site in March, 2010. As the earthquake observation at the Base-isolated Important
Building of Fukushima Dai-Ichi NPP had only begun from February 21, 2011 to examine theperformance of base-isolation, valuable data by the Great East Japan Earthquake could only becollected for 20 days after starting observation.
By examining the observation records and conducting simulation analysis, it was confirmed thatthe Base-isolated Important Building possessed sufficient base-isolation performance for thehorizontal motion and that the seismic design of the building was adequate. For these reasons, thebuilding suffered no damage from the Great East Japan Earthquake and demonstrated satisfactory
performance as an “Emergency Headquarter.”.

REFERENCESTEPCO (2007). “Damage of Kashiwazaki-Kariwa Nuclear Power Plant site in the Niigataken
Chuetsu-oki Earthquake in 2007” http://www.tepco.co.jp/nu/kk-np/chuetsu/another-j.html.

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