13th World Conference on Earthquake Engineering
Vancouver, B.C., Canada
August 1-6, 2004
Paper No. 1199

SEISMIC ISOLATION RETROFIT OF A PREFECTURAL
GOVERNMENT OFFICE BUILDING
Yoe MASUZAWA1 and Yoshiaki HISADA2

SUMMARY
The main office building of the municipal government of Yamanashi prefecture, Japan, was retrofittedwith a seismic isolation system as a measure against earthquake vibrations, which is the first of its kind asa prefectural government office. Strong ground motions from a seismic fault along the Itoigawa-Shizuoka
tectonic line, which is one of the largest active faults in Japan and about 15 km distance to the building,were simulated as input ground motions. In addition to the regular seismic design based on the Japanesebuilding code, a performance-based design was adopted to evaluate the retrofitting results. Consequently,
it was estimated that the retrofitted building would secure its operability as a municipal government
office, even after the largest earthquake. The building was isolated at the intermediate story between the
ground floor and the basement. A new temporary supporting system based on post-tensioned units wasdeveloped in order to place the isolators efficiently and to secure an enough office space by eliminating
the conventional supporting structure, which is inevitably left even after the retrofit work and thus limits
the space available. Before the construction started, full-scale experiments were conducted to confirm
safety and high performance of the system.
INTRODUCTION
The seismic isolation system of a building is one of the most effective and the most practicablecountermeasures against earthquakes, because it drastically reduces its acceleration response during
earthquakes. Therefore, when we planed to retrofit the 40 year-old municipal government office of
Yamanashi prefecture, we adopted the seismic isolation system not only to improve its seismic safety andfunctionality, but also to keep its original design. In addition, it is the best method not to obscure its usage
as an office building during the retrofitting works.
When we assessed a seismic retrofitting design, it was important to verify the seismic performance against
appropriate earthquake ground motions. In our case, we simulated strong ground motions using a hybrid
method (Hisada [1]) by considering a seismic fault on the Itoigawa-Shizuoka tectonic line, which exists in
1

Structural Designer, Architectural Design Division, Yokogawa Architects & Engineers, Inc., 2-20-28,
Shimomeguro, Meguro-ku, Tokyo 153-0064, JAPAN. E-mail: masuzawa@yae.co.jp
2
Professor, Department of Architecture, Kogakuin University, 1-24-2, Nishi-Shinjuku, Shinjuku-ku,
Tokyo 163-8677, JAPAN. E-mail: hisada@cc.kogakuin.ac.jp

the vicinity of the site. Then, we evaluated the effectiveness of the retrofitting in accordance with aperformance-based design; the building needed to ensure not only the safety but also the operability as thegovernment office building even during and after the largest earthquake.
The seismic isolation retrofit was achieved by setting up seismic isolation devises on the lower groundfloor. In order to maintain functions such as restranrant and office at the basement floor, we developed a
new temporary supporting system based on a post tension unit, which was able to secure an enough spaceon the isolation floor after the retrofit (Masuzawa [2]). Before the construction started, full-scale
experiments were conducted to confirm the safety and high performance of the system (Yamada andMasuzawa [3]). The seismic isolation retrofit construction was completed in September 2002, through theterm of works of about 14 months. To evaluate the effects of the seismic isolation, microtremor
measurements in the building were carried out before and after the retrofitting works (Toshinawa et al.
[4]). After the retrofitting, Building Research Institute of Japan installed accelerometers in and around thebuilding (Toshinawa et al. [5]).
In this project, in addition to the improvement in the seismic performance by the seismic isolation retrofit,
the renovation of the entire building was carried out; building's interiors and equipments were completely
renewed, and the external walls and the building frames were repaired. Consequently, it was estimatedthat about 50 % of the cost was reduced as compared with the cost of creating a new building (Masuzawa[6]).
DESCRIPTION OF BUILDING
The main office building of the Yamanashi Prefecture municipal government is shown in Figure 1. Thisbuilding is designed by Dr. Tachu Naito, who is famous for the inventor of the seismic shear wall. The
building is the center of prefecture’s administration including governor's secretariat office, which wasbuild in 1963. It is a reinforced concrete building with eight stories on the ground, one basement and threestories in penthouse. The description of the building is shown in Table 1.
Table 1 Description of building
Address

1-6-1, Marunouchi, Kofu city,
Yamanashi prefecture, JAPAN

Design Years
1961
Completion Years 1963
Building Area
1,174.20m2
Architectural Area 10,035.45m2
Eave Height28.20mThe Highest Height 37.10m
Structural Kind
Reinforced concrete construction
Structural Type
Frame structure with shear wall
Foundation Type
Spread foundation

Figure 1 East side front panorama
PERFORMANCE-BASED DESIGN
Input earthquake ground motion
When we conduct a performance-based design, one of the most important key parameters is to use
appropriate strong ground considering its seismic circumstance. The building site is located at about 15km

distance to the Itoigawa-Shizuoka tectonic line, which is regarded as the highest possibility of earthquake
occurrence around the area. Seismic fault model is shown in Figure 2. We used a hybrid method tosimulate strong ground motions, which combined theoretical and empirical methods at lower and higher
frequencies, respectively (Hisada [1]). We took into account the south section and a part of the middle
section of the tectonic line as the fault model. Accordingly, the estimated fault length is about 70 km, andthe corresponding JMA magnitude and moment magnitude are 7.9 and 7.2, respectively. The groundproperty model assumed nine layer model shown in Table 2. S-wave amplification over the bedrock(Layer No. 7) is provided in Figure 3. The earthquake ground motions were calculated by two asperity
models. We adopted the results showing the largest response spectrum at the site as the input groundmotion for the seismic design. Figure 4 and Figure 5 show the response spectra and time history
waveforms, respectively.
Seismic fault model
Rupture initiation point

Building site

Mt. FUJI

0

20

40km
The Headquarters for Earthquake Research Promotion

Figure 2 Itoigawa-Shizuoka tectonic line seismic fault model
Original figure: The Headquarters for Earthquake Research Promotion (www.jishin.go.jp/)
Table 2 Ground property model
3

Layer No.

ρ(g/cm )Vp(m/s)Vs(m/s)

Qp

Qs

H(m)

1

2.06

2395.01166.0

200.0

100.0

2.6

2

2.26

2938.01380.0

200.0

100.0

8.4

3

2.32

3535.01698.0

200.0

100.0

10.0

4

2.29

3333.01504.0

200.0

100.0

10.0

5

2.33

3693.01756.0

200.0

100.0

569.0

6

2.50

5500.03000.0

200.0

100.0

1400.072.70

6000.03510.0

300.0

150.0

17500.08

3.00

6800.03930.0

500.0

300.0

10000.09

3.20

8000.04620.01000.0500.0－

Figure 3 S-wave amplification

Figure 4 Response spectra

Figure 5 Time history waveforms of acceleration, velocity and displacement

Seismic design
We designed the retrofitting by following the current seismic building code to maintain the functions of
the public office building by improving its seismic performance, such as by preventing falls or damages ofimportant facilities like computers and furniture during the large earthquake. Using the load incremental
method considering the inelasticity of the structure, we estimated the ductility of the building for theearthquake. As a result, we set the target value of the story deflection angle of the building to be 1/500
radian or less. We assumed the state of the structural member to be less than shear failure with the yieldhinges in some boundary girders allowed. We also assumed that the criterion of the seismic isolation
device deformation was within a safety deformation level (i.e., shear strain 200 % = 33 cm in this case),and the under structure was less than allowable stresses. To prevent the damage of non-structuralmembers and equipment, we assumed the horizontal response acceleration to be within 200 gal on theoffice floors (the 1-8th floor). We evaluated the seismic performance of the retrofitted building based on
dynamic response analyses using both the input ground motions required by the building code and thesimulated ground motions above-mentioned. The result satisfied all the target values. The analyticalresults are provided in Table 3.
Table 3 Results of dynamic response analysis
Level2(Standard case)Upper
structure

RandomItoigawaShizuoka
tectonic line

1/2011
7F
1/731
8F
0.172
7F
0.461
8F

1/15095F
1/1036
5F
0.213
5F
0.323
4F

29.6

14.9

31.0

19.3

30.5

15.2

30.8

111

118

180

90

188

131

111

117

185

92

187

X

0.110

0.100

0.104

0.132

0.090

0.136

Y

0.110

0.100

0.103

0.135

0.091

0.136

Direction

Elcentro
1940 NS
1/2174
5F
1/933
8F
0.148
5F
0.361
8F

Taft 1952
EW
1/22297F
1/1042
8F
0.156
8F
0.323
8F

Hachinohe
1968 NS
1/2692
7F
1/1148
8F
0.129
7F
0.293
8F

Kobe 1995
NS
1/1683
5F
1/845
8F
0.191
5F
0.398
8F

X

21.4

18.3

19.4

Y

21.6

18.3

Maximumshear strain
(%)

X

130

Y

Maximumbase shear
coefficient

Maximum
story
deflection
angle

X

Maximum
ductility
factorX

Maximumhorizontal
deformation(cm)
Seismic
isolation
deviceInput earthquake ground motion
Building code (Kokuji1461) /The lower shows the phase characteristic modelY

Y

SEISMIC ISOLATION RETROFIT SYSTEM
Outline of construction method
The building was isolated at the intermediate story between the ground floor and the basement, where it
was used for electronic and air-conditioning facilities before the retrofitting. We planned that thosefacilities were renewed to the rooftop, and the lower floor was converted to a space for restaurant andoffice. Consequently, the lower floor, which became the seismic isolation layer, required keeping enoughspace. On the other hand, when the columns of the floor were cut to set up seismic isolation devices, it
was necessary to support temporarily the upper building. Because it is very important to secure the safetyof a building during the set up, it is common to build permanent supporting columns; they result to reduce
the floor space. In order to carry out the seismic isolation retrofit works effectively and to secure enoughspace by eliminating unnecessary supporting structures after the retrofit, we developed a new temporarysupporting system between upper and lower structures using post-tensioned units. The seismic isolation
system consisted of forty lead rubber bearings, which were installed to columns, and did not require
external dampers. Figure 6 and Figure 7 represent the basement floor plan and the cross section,
respectively.
Air drain

Elevatorlobby

EV
KitchenLavatory
Stairs Locker

Warehouse Machine room

DiningStall

Barber shop

OfficeSyringing room
Air drain

Seismic isolation device
Lead Rubber Bearing

Library

LRB 750φ x８
LRB 700φ x３２

Figure 6 Basement floor plan

Elevator lobby

OfficeOfficeElevator lobby
Elevator lobby

OfficeElevator lobby

OfficeElevator lobby

Conference room

Elevator lobby

Expansion joint

External wall repair

External fittings
repairElevator lobby

Elevator lobby

PH2F
PH1F

Seismic isolation

4000

Elevator lobby

Entrance

PH3F

3600

OfficeRF3500 3500

New establishment
equipment

3500 3500 3500

3500 2600 2600 2300

Seismic isolation of elevator

3600

Non-seismic isolation Seismic isolation

Non-seismic isolation
6000

2500

7750

3700

7750

Figure 7 Cross section

Seismic isolation device

8F
7F
6F
5F
4F
3F
2F
1F
B1F

Temporary supporting system
We developed the temporary supporting system based on a frictional force using the pre-stress of PC
cables. The details of the temporary supporting system are shown in Figure 8. The main features of thesystem are shown below.
①Steel brackets are fixed on RC columns using pre-stress of the PC cables, and the axial forces of thecolumns are temporarily supported by the bracket using the frictional forces on the bond surfaces between
the brackets and the column. Shear cotters are installed on the bond surfaces, and the non-shrink mortars
are filled between the columns and the brackets.
②The PC cables, which penetrate the column, are aligned in one direction, and the steel brackets andhydraulic lifters are set in the orthogonal two directions.
③Using the PC strand cable and screw-type anchorage devices, we can expect not only large pre-stressing
forces without setting loss, but also easy removal and reuse of the cables.
A big advantage of this construction method is to make both the supporting structure and the construction
space compact.
Reinforcement concrete

50

400

100

300

462. 5

Existing column
Steel bracket

110 110520

250

1, 500

D13

325

575

1, 500325462. 5300

PL- 45
D13

425

650

425

100

400

50

Bond surface of a steel bracket

PC cable( SEEE F200)

1, 8501, 8501, 2201, 500

400
1500

330

330

Tension machine330

4, 0004, 000600

Hydraulic lifter
200tf

330

600

Tension machine
Seismic isolation
deviceShear cotter bar
50

425

50

650
1, 500425

PC cable( SEEE F200)

Non-shrink mortar

400

700
1, 500Figure 8 Temporary supporting system (four-cable type)400

2, 1502, 150

Steel bracket
Steel bracket

Full-scale experiment
Before the construction started, we conducted full-scale experiments to imitate the actual construction
scheme and to confirm the safety and the support performance of the temporary supporting system. In
addition, we investigated the coefficient of the friction and the axial force-deformation relation of the PC
cables. Outline of the experiment and specimens are shown in Figure 9 and Table 4, respectively. Since
the capital and the pedestal of a column have a same mechanism, only the capital was modeled, and theactual-sized specimen with 1.5 square meters was produced. We made four specimens of two types
according to the design axial forces of the columns: two of four-cable type, and two of six-cable type. In
order to reproduce the actual construction scheme as much as possible, we made the columns same as theoriginal, and then constructed the reinforcement columns around the columns. Figure 10 shows thesituations of the experiment.
Examples of the load-displacement relations are shown in Figure 11 and Figure 12. In four-cable type,the vertical displacement was about 0.2 mm at 500 tf loading (equal to 150% of the design load), and in
six-cable type, that was also about 0.2 mm at 750 tf loading (equal to 150% of the design load). These
values are sufficiently small for the temporally construction. The sliding displacement on the bonded
surface was not observed until it reached the maximum load, as clearly seen in the load-displacement
curves. Also, we conducted load continuation examination for two weeks (a period for temporary support)
using specimen No.4 (six-cable type), and confirmed that the sliding displacements on the bonded surface
were negligible under the pressure of 120% of the design load. We also confirmed from the loading
experiments that the coefficient of the friction was at least 1.86 and more, which agreed with the previous
results (Kawamata [7]). Therefore, we concluded that this construction method was very safe.
Pressurizing testing machine (Max: 1200tf)(Bearing surface diameter: 625mm)
Bearing steel plate (t=50mm, 1050mmX1050mm)(Bonded surface: Dry packing)Dial gauge: four totals(Supplementary measurement for column joint sliding)
1550

700
1500

Non-shrink mortar filling (t=50mm)
Dial gauge: four totals(Measurement for bracket sliding confirmation)
PC cable (SEEE F200, Four cables/Six cables)
Steel bracket (Four-cable type/Six-cable type)

Foundation

Hydraulic lifter: four totals(Reaction measurement): Existing column (700mmX700mm)

Dial gauge: four totals(Main measurement for column joint sliding)Figure 9 Outline of experiment
Table 4 Outline of specimens
Concrete strength
Specimen

Existing column Reinforcement(kgf/cm2)

No.1
No.2
No.3
No.4

150

(kgf/cm2)360

PC cable strand
Number ofcables4
4
6
6

Prestress(tf/cable)

Design loadof column
(tf)

134

333.3

134

504.8

1) Tension of PC cable2) Loading examination
Figure 10 Situations of experiment (four-cable type)
1200

1000

Vertical load (tf)

800

600
Bracket gauge No.5
400

Bracket gauge No.6
Bracket gauge No.7
Bracket gauge No.8

200

Design load=333.3tf
Design loadx1.5=500tf
0
0.00

-0.10

-0.20

-0.30

-0.40

-0.50

-0.60

-0.70

-0.80

Vertical displacement (mm)Figure 11 Experimental results (four-cable type)
1200

Vertical load (tf)

1000

800

600
Bracket gauge No.5
400

Bracket gauge No.6
Bracket gauge No.7
Bracket gauge No.8

200

Design load=504.8tf
Design loadx1.5=750tf
0
0.00

-0.10

-0.20

-0.30

-0.40

-0.50

-0.60

Vertical displacement (mm)Figure 12 Experimental results (six-cable type)

-0.70

-0.80

Construction of Seismic Isolation Retrofit
A plan showing the arrangement of the seismic isolation devices together with the design reaction forces(the axial forces of the columns on the seismic isolation layer) is shown in Figure 13, and the construction
process of the temporary supporting system is shown in Figure 14. We adopted the new supporting
method at the capitals of the columns, and used a conventional supporting method on foundation girders
at the pedestals of the columns. We used four 200 tf hydraulic lifters on one column as the preloading
jacks, and scheduled four sets of the temporary supporting systems and the seismic isolation devices as
one unit on the construction process. As shown in the construction flow in Figure 13, we rotated thetemporary supporting construction system from the X1 axis to the X10 axis, one by one. To support thebuilding during the retrofitting, we also constructed a temporary steel frame structure with braces, which
was easy to build and to remove. We always kept the seismic shear coefficient of 0.2 during theconstruction using the temporary steel structure and other seismic resistant elements.
The reaction forces of the jacks on columns have been measured using pressure converters during
construction. We also measured the displacements at 20 points on the capitals of columns using digital
dial gauges (1/100mm): three points per column along preloaded lines, and two points in a line
immediately after the installation of the seismic isolation devices. 3 mm of the relative displacement
accuracy (1/2000 of span) has been allowed as the standard of the temporary supporting construction.
We first loaded up to 120% of the design reaction force in each column following the pressure step
divided into eight, and confirmed reasonable reaction-displacement relations. Then, we reduced thepressure down to the designed reaction divided into two steps. Five-minute interval was taken after eachstep to fix the balance of the preloading columns. When we removed the jacks, we followed the reversed
steps of preloading by measuring the vertical displacements in each step. The measurements of relative
displacement on the capitals immediately after preloading are indicated in Figure 15. In all measured
capitals, the measurement displacement values ware less than the permissible value (equal to 3mm).
Reaction pressures during the retrofitting construction and the results of the vertical displacements at acapital are shown in Figure 16 and Figure 17, respectively. Since we set free the axial stress in thecolumn immediately after cutting the column, the pressure of the jack and vertical displacement
fluctuated. We speculate that the fluctuations not related to the cutting were probably caused by thechange of the live load (increase during working hours) and the load shift by stiffening the grout in theanchorage zone after setting the seismic isolation devices. The maximum vertical displacement during the
temporary supporting construction period were also satisfied the permissible value. Figure 18 shows
comparison simulations and observations about axial force of columns. Observations indicate
measurement values immediately after cutting of the column. The average ratio of the design pressureswith respect to the measurement pressure was 109 % using 36 columns. The values of the ratios were
within a range of 93 % - 142 %, which indicated the accuracy of the design. Figure 19 shows the actual

situations of the seismic isolation retrofit works and the completion.

Flow of seismic isolation construction
Four-cable type

200

Y1

281.4

416.9

434.5

468.8

450.2

289.7

303.8

311.3

252.7

318.8

328.0

442.3

472.8

504.8

474.0

333.1

333.3

293.8

256.8

316.1

332.0

354.6

365.7

370.3

363.6

337.3

313.7

254.4

225.2

274.5

288.6

321.6

286.9

290.3

323.1

284.6

271.7

215.2

6,000

6,000

6,000

6,000

6,000
54,000

6,000

6,000

6,000

6,000

7,750

268.8

Y4

200

7,750

Y3

Four-cable type214.0

19,2003,700

Y2Six-cable type

X1

X2

X3

X4

X5

X6

X7

X8
Sign

Jack operation of one row (Four columns) at the same period

X9

X10

Number of
Seismic
isolation device installation
18
LRB700A
14
LRB700B
8
LRB750Figure 13 Layout of seismic isolation devices with design reaction force of column (tf)1

Frame in existing building

Reinforcement of column

2 and girder

Bracket and support installation

3 PC cable insertion and tension

4

Hydraulic lifter installation
Temporary supporting1FL

PC cable
Steel bracket
HydrauliclifterSteel support
B1FL

Wire saw installation and5 existing column cutting

6 Existing column removal

Seismic isolation device

7 installation and fixation

Removal of temporary supporting

8 Seismic isolation retrofit completionNon-shrink mortar
Wire saw

Seismic isolation
deviceFigure 14 Seismic isolation retrofit construction process

Relative displacement (mm)

3
2.5
2
1.5
1
0.5
0
200

250

300

350

400

450

500

550

Preloading load (tf)Figure 15 Preloading load (equal to design reaction) - relative displacement relations
140

Preloading load (%)

120
100
80
60

Grouting for LRB fixation

Column cutting

40
Down of jacks

Preload

20

X8/Y1

X8/Y2

X8/Y3

X8/Y4

0
0

24

48

72

96

120

144

168

192

216

192

216

Time (h)Figure 16 Time history of preloading load

Relative displacement (1/100mm)

200
150
100
50
0
0
-50
-100

24

48

72

Column cutting
Preload
X8/Y1B

96

120

144

168

Grouting for LRB fixation
Down of jacks
X8/Y2B

X8/Y3B

X8/Y4B-150
Time (h)Figure 17 Time history of relative displacement

600
1.2
Observed reaction (tf)

500

1.0
0.8

400
300
200
100

Ave. 1.09 σ 0.11
0
0

200

400

600

Simulated load (tf)Figure 18 Relation between simulated load and observed reaction

1) Temporary supporting system

2) Seismic isolation retrofit completion

3) Dining after retrofit

4) Seismic isolation device and fireproof panels

Figure 19 Situations of the seismic isolation retrofit and the completion

CONCLUSION
We adopted a seismic isolation retrofit system to the main office building of the Yamanashi prefecture
municipal government. We computed the input ground motion from the Itoigawa-Shizuoka tectonic line,
which is one of the largest-scale active faults in Japan and is located at about 15 km to the site, andevaluated the retrofitting based on a performance-based design. We concluded that the retrofitted building
would ensure not only safety but also the operability as the government office even during and after thelarge earthquake. The building was isolated at the intermediate story between the ground floor and thebasement. In order to construct the seismic isolation retrofit effectively and to secure enough space byeliminating unnecessary supporting structures after the retrofit, we developed a new temporary supporting
system using post-tensioned units. Before the construction started, we conducted full-scale experiments toconfirm the safety and high performance of the supporting system. From the measurements during
construction period, the simulated results agree well with the observations, also the vertical displacementof the capitals satisfied design criteria.
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1.

2.

3.

4.

5.

6.
7.

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Earthquakes in Subduction Zones." Proceedings of the 12th World Conference on Earthquake
Engineering, Auckland, New Zealand, 763/4/A, 2000.
Masuzawa, Y. “Temporary supporting system for seismic isolation retrofitting at the intermediate
floor Part 2: Outline of the construction scheme and the observation.” Proceedings of the Annual
Meeting of Architectural Institute of Japan, B-2, 473-474, 2003. (in Japanese)
Yamada, T. and Masuzawa, Y. “Temporary supporting system for seismic isolation retrofitting at
the intermediate floor Part 1: Supporting system and the full-scale test.” Proceedings of the Annual
Meeting of Architectural Institute of Japan, B-2, 471-472, 2003. (in Japanese)
Toshinawa, T., Hoshino, Y., Masuzawa, Y. and Yoshiaki, H. “The effects of seismic retrofitting on
vibration characteristics - A case study on the main building of Yamanashi prefectural government.”
Proceedings of the 58th Annual Conference of the Japan Society of Civil Engineers, CD-ROM,
2003. (in Japanese)
Toshinawa, T., Hoshino, Y., Masuzawa, Y., Kashima, T. and Hisada, Y. “Low-strain Vibration
Characteristics of a Prefectural Government Office Building with Seismic Isolation Retrofit,
Yamanashi, Japan.” Proceedings of the Asia Conference on Earthquake Engineering, Manila,
Philippine, 2004.
Masuzawa, Y. “A Main Office Building of A Yamanashi Prefecture municipal Government.”
Contemporary Architecture, Vol.57, 58-61, 2003. (in Japanese)
Kawamata, S. “Earthquake disaster restoration of a building No.5, Tohoku Institute of Technology.”
The Kenchiku Gijutsu, No.346, 1986. (in Japanese)
ACKNOWLEDGMENT

We thank all the members of General Affairs Department of Yamaguchi Municipal Government for theircooperation and understanding through the design and construction periods. Also, we would like toexpress our gratitude to all the members of the construction work including Yokogawa construction Co.,
Ltd., which was in charge of the experiment and the construction management.