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Title:
Structural Design of Base-Isolation system for Tall Building in Japan
Authors:
Yozo Shinozaki, Structural Engineer, Taisei Corporation
Osamu Hosozawa, Structural Engineer, Taisei Corporation
Tsutomu Komuro, Structural Engineer, Taisei Corporation
Subject:
Structural Engineering
Keywords:
Design Process
Structure
Publication Date:
2004
Original Publication:
CTBUH 2004 Seoul Conference
Paper Type:
1.
2.
3.
4.
5.
6.
Book chapter/Part chapter
Journal paper
Conference proceeding
Unpublished conference paper
Magazine article
Unpublished
© Council on Tall Buildings and Urban Habitat / Yozo Shinozaki; Osamu Hosozawa; Tsutomu Komuro
Structural Design of Base-Isolation system for Tall Building in Japan
Yozo Shinozaki1, Osamu Hosozawa1, Tsutomu Komuro1
1
Structural Engineering Group, Design Division, Taisei Corporation
Abstract
The high-rise buildings with the base isolation system have been realized by studying the practical applicability of
this system, that is, by extracting and resolving the several problems in the actual design. Sendai MT building is
the first base-isolated building with over 60 m height in Japan, and Thousand Tower was the tallest base-isolated
residential Tower in Japan when completed. With the base isolation system, it is possible for the high-rise
buildings to possess not only the high seismic performance, but also the flexible planning in the design, using high
strength materials and long span structure systems as well.
The seismic data were recorded from the seismographs in Sendai MT building, when the Off -Miyagi
earthquake occurred in May 26, 2003. ®
These data showed that the base isolation
system acted effectively on the
©
high-rise building..
Keywords high-rise building, base isolation system, sliding bearing, rubber bearing, high strength materials
1. Introduction
The construction of base-isolated structures in Japan
began about 20 years ago, during the 1980s. Currently
approximately 100 such structures are constructed in
Japan each year, and the total number of base-isolated
structures exceeds one thousand. At the base-isolated
structures, most of energy input from an earthquake is
mainly absorbed by the base isolation devices. So the
base isolation system can minimize the damage of
superstructures and maintain the buildings' functions
even after severe earthquakes. However, up to our
proposal, this excellent system had been applied only
to the low-rise buildings with natural period shorter
than 1 second, and has been regarded as ineffective to
the high-rise buildings. In the study of the high-rise
buildings with the base isolation system, the authors
faced the following design problems.
(1) The response reduction effect of the base isolation on
the high-rise buildings was not clear.
(2) The base isolation system in the high-rise buildings
might make the habitability worse in the case of
strong winds.
(3) The adoption of the base isolation system might
cause the construction cost to be significantly higher.
(4) The property and stability of the large size rubber
bearings imposed tensile force on were unknown.
2. EFFECT ON HIGH-RISE BUILDINGS
With regard to the problem (1) mentioned in the
introduction, the parametric analyses [Ogura et al,
1997] were conducted to make the response reduction
effect of the base isolation system clear for the
low-rise to high-rise buildings consecutively.
Figure 1 shows the 2-mass model of the base isolated
structure, representing the superstructure and the base
isolation story as the two mass-points, respectively. The
superstructure is assumed to be reinforced concrete
frame and the base isolation system is to be the type of
the hysteretic energy absorption. The force-displacement
relation and the hysteretic rule of the springs are shown
in Figure 2. With this model, the seismic response
analyses were conducted under the seismic ground
motion, El Centro (1940-NS, amplified with the max.
velocity to be 1.00 m/sec) and the artificial seismic wave
of BCJ-L2 (the max. velocity is 0.574 m/sec). The
parameters are the natural period of the superstructure,
varied to be from 0.2 to 5.0 by 0.2 second.
Superstructure
Ws
Spring 1
Base isolation Story
Contact Author: name, position, affiliation, address
Yozo Shinozaki
Structural Engineering Group, Design Division, Taisei Corp.
1-25-1 Nishi-Shinjuku, Shinjuku-ku, Tokyo 163-0606, JAPAN
Tel: 81-3-5381-5244 Fax: 81-3-5381-5246
e-mail: [email protected]
Wi
Spring 2
Ws:Wi=4:1
Figure 1 Analysis model
CTBUH 2004 October 10~13, Seoul, Korea
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Shear Force
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Figure 2 Properties of Springs
Response Ratio
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Reduction Effect
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EL CENTRO '40NS 1.0 m/s
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㪌㪅㪇
Natural Period of Superstructure (sec)
Response Ratio =
Response of base-isolated structure
Response of non-base-isolated structure
Response Displacement
of Base Isolation Story (mm)
Figure 3 Response Displacement of Superstructure
㪍㪇㪇
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EL CENTRO '40NS 1.0 m/s
㪋㪇㪇
㪊㪇㪇
BCJ-L2 0.574 m/s
㪉㪇㪇
base isolation system, the combined use of the sliding
bearings and the rubber bearings is developed, called
Hybrid TASS system (Hybrid TAISEI shake suppression
system). In this system, the yield shear force and the
stiffness of the base isolation story can be easily
designed by setting the ratio of these two type bearings
and the stiffness of the rubber bearings. So this system
can be widely applied to the low-rise to the high-rise
buildings.
In the design of the high-rise buildings with the base
isolation system, the stiffness of the system is designed
to be as soft as possible to make the natural period long.
However the initial soft stiffness of the ordinal
base-isolation system might make the habitability worse
in the case of strong winds (See Figure 5). Against this
problem, which is mentioned in the introduction as the
problem (2), Hybrid TASS system is effective. Figure 5
shows the typical force-displacement relation of Hybrid
TASS system. To set the yield shear force of the base
isolation story larger than the design wind force, the
initial stiffness of the whole structure maintains almost
the same as the building without the base isolation
system. And to make the stiffness after the yield
particularly soft, the high seismic performance can be
expected in the case of hard earthquake attacks.
Shear Force
Shear Force
㪈㪇㪇
Earthquake
Earthquake
㪇
㪇㪅㪇
㪈㪅㪇
㪉㪅㪇
㪊㪅㪇
㪋㪅㪇
㪌㪅㪇
Natural Period of Superstructure (sec)
Figure 4 Response Displacement of Isolation Story
Figure 3 and Figure 4 show the response displacement
of the superstructure and that of the base isolation story
respectively, corresponding to the varied natural period
of the superstructure. In Figure 3, the response showing
with the vertical axis is defined to be the ratio of the
response displacement to that of the case without the
base isolation system.
From Figure 3, it is found that the response reduction
tends to decrease in proportion to the increase of the
natural period of the superstructure. But even when the
natural period is 3-4 second, the response displacement
can be reduced up to around 30-40% of the case without
the base isolation. And the response displacement of the
base isolation story is approximately 300-400 mm, so the
response of the base isolated structure is considered to be
very stable.
Judging from these results, if the design of the yield
shear force and the stiffness after the yield of the base
isolation story is appropriate, it is possible even for the
high-rise building to obtain the high seismic
performance.
Wind
Wind
Equivalently-soft
soft stiffness
hard stiffness
Deformation
Ordinal system
Deformation
Hybrid TASS system
Figure 5 Force-Displacement Relation
Moreover, Hybrid TASS system is economically
reasonable. Figure 6 shows the comparison between
Hybrid TASS system and the ordinal base isolation
system. In the ordinal system, the dampers such as the
steel or lead energy absorption devices are necessary
besides the isolators under the columns, while only the
sliding and rubber bearings under the columns in Hybrid
TASS system. So by the application of Hybrid TASS
system, the high-rise building with the high seismic
performance can be achieved without large increase of
the construction cost.
Rubber bearings
Rubber bearings
Steel damper
Sliding bearings
Lead damper
3. BASE ISOLATION DEVICES
To obtain the effective force-displacement relation of the
CTBUH 2004 October 10~13, Seoul, Korea
Figure 6 Comparison of Hybrid TASS System and
Ordinal Base Isolation System
4. TESTS ON TENSILE PROPERTY OF
RUBBER BEARING
In the design of the slender high-rise building, the uplift
due to overturning and vertical forces during a large
earthquake might act on the isolators especially at the
corner. However, the property of large size rubber
bearings subjected to the tensile force was unknown
(problem (4)). In order to understand the tensile
properties of the large rubber bearings, the tensile
loading tests [Muramatsu et al, 2001] were carried out
(Photo 1). Figure 7 shows the test specimen with the
diameter of 1200mm. The relation between tensile and
shear strain is shown in Figure 8, where the test results of
these large size tests are plotted, together with those of
the bearings with small diameter from other tests
[Takayama et al, 1995]. There is a large difference of the
safety limit between the small and the large size rubber
bearings.
Considering this tendency, the hatched part in the
figure is decided as the criteria in the design. There is an
enough margin of the safety with respect to the limit of
the tensile strain.
Photo 1 Test on Tensile Property
㪉㬍㪊㪉㪄㪤㪉㪇
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Figure 7 Test Specimen
Expected measured line of tensile strain limit
(㱢 500) by Ref. [Takayama]
٤ 㱢1200 test result㧔no failure)
٨ Ǿ1200 test result ( failure)
ً Ǿ 500 test result ( failure)
Tensile strain
Design Criteria
5. DESIGN OF HIGH-RISE BUILDINGS WITH
HYBRID TASS SYSTEM
5.1 Sendai MT Building
Sendai MT Building is the 18-story office building with
the height of 84.9m, located in Sendai City, Eastern
Japan [Ogura et al, 1997]. This building is the first
base-isolated building with over 60 m height in Japan
(See Photo 2)
The structural features of this building are follows.
1) Use of the high strength materials such as concrete
with compressive strength of 60N/mm2 and SD 490
re-bars for the longitudinal reinforcement of the
beams and the columns.
2) Application of the hybrid structure beams for the
15m-long spans. This beam consists of steel for the
mid part and reinforced concrete for the both the ends
of the beam.
3) The high-rise buildings with the base isolation system
for the high seismic performance.
The client required the high seismic performance and
the ability of the function maintenance after a large
earthquake. To be satisfied this requirement, the
application of the base isolation system, Hybrid TASS,
was examined. Moreover, in order to obtain the large
office space (See Photo 3), the long span beam system
and the high strength materials were used . Figure 9
shows the frame elevation. The columns and the beams
are the pre-cast members to ensure the quality of the
structure and to make the construction term short
possible.
Figure 10 shows the arrangement of the isolation
devices at the isolation story below the first floor. The
ratio of the sliding bearings among all the bearings under
the columns was designed so that the yield force might
be larger than the wind force. And to make the stiffness
after the yield soft, the shape and rubber stiffness of the
rubber bearings were designed. The sliding bearings are
installed mainly under the inner columns, where the
fluctuation of the axial force due to seismic forces is
relatively small.
The seismic response analyses were conducted to
confirm the target seismic performance, using several
seismic ground motions. The input levels of the motions
are categorized from the level 1 to the level 3,
considering the occurrence probability during the use
period of the building. Figure 11 shows the maximum
response story drift angle. For the level 2 the drift angles
are less than 1/330 and for the level 3 less than 1/230.
From these results, the seismic design targets are
satisfied and the high seismic performance is confirmed.
㱢 1200 test
Shear strain
Figure 8 Relation of Tensile and Shear Strain
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Figure 10 Arrangement of Isolation
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Photo 2 Sendai MT Building
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Figure 11 Maximum Response Story Drift
Photo 3 Sendai MT Building (Office Space)
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CTBUH 2004 October 10~13, Seoul, Korea
5.2 Thousand Tower
Thousand Tower is the residential Tower situated in
Kawasaki City, Kanagawa Prefecture, and is the
reinforced concrete structure with 41 stories above
ground [Kawabata et al, 2001] (Photo 4). The base
isolators place at the isolation story below the first floor.
Figure 12 and 13 shows the frame elevation and the
structural plan, respectively. The total height is 135.0 m
and the aspect ratio is 3.83 in Y directions, so this
building is the relatively slender structure.
The pre-cast and pre-stressed concrete beams as
shown in Figure 14 are used for the 12m-span. The
pre-stressing steel tendon is arranged at the clear
mid-span of the beam and the longitudinal reinforcement
of the steel bars is through the beam and developed at the
beam-column joints. By adopting this long span system,
no column exists in the residential area.
The high-strength concrete with strengths up to 100
N/mm2 is used for the columns and the high strength
re-bars (SD 490, USD 685) used for the longitudinal
reinforcement of the beams and the columns. By using
these high strength materials, the number and the
cross-section of the structural members can be reduced,
so that the effective architectural space can be used for
the planning.
The seismic response analyses were conducted using
several artificial ground motions, (see Table 1). The
artificial ground motion H is based on the seismic
activity and the soil properties at the building location.
The level 2 maximum response of the isolation story
in Y direction is shown in Fig. 15. The level 2 maximum
response story drift angle in Y direction is shown in Fig.
16. Compared with the response of the non-isolated
model, the responses are effectively reduced by the base
isolation system.
Shear force [kN]
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sliding bearing
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rubber bearing
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Figure 15 Maximum Response
of Isolation Story
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25
Photo 4 Thousand Tower
Figure 12 Frame
Elevation
20
15
10
5
0
0
0.005
0.01
0.015
Maximum Response story drift angle [rad]
Figure 16 Maximum Response Story
Figure 13 Structural Plan
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Table 1 Seismic waves
BCJ-L2
Artificial wave H
Level 1
2
(m/s )
㪄
0.237
Level 2
2
(m/s )
0.574
0.474
Level3
2
(m/s )
㪄
0.595
6.SEISMIC RECORD AT OFF-MIYAGI QUAKE,
MAY 26, 2003
The seismic data were obtained from the
seismographs set at the floors of the isolation story,
the 1st, 10th and 18th stories, in Sendai MT building,
when the Off -Miyagi earthquake occurred in May 26,
2003 The maximum accelerations at these floors are
shown in Table 2 and the acceleration waves of the
E-W direction shown in Figure 17.
Photo 5 shows the observed track of the relative
displacement between the 1st floor and the floor below,
which means the displacement of the isolation story.
From this result, the maximum displacement of the
isolation story is found to be about 20mm and there is no
remain displacement. Considering with the relation
between the force and the displacement in the design, the
sliding occurred and the isolation system is thought to
have acted well.
With the recorded ground motion, the response
analyses using the design model were carried out. Figure
18 shows the comparison of the analyzed and recorded
maximum acceleration. Figure 19 shows the
displacement track of the isolation story from the
analyses. The good correspondences between the
analyses and the records are found in these charts.
From these data and the analyses, it can be said that
CTBUH 2004 October 10~13, Seoul, Korea
the base isolation system acted effectively on the
high-rise building and the design analysis model is
adequate.
5
Table 2 Maximum Accelerations
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1. The authors applied the base isolation systems to
the high-rise buildings as a pioneer, getting out of
the conventional ideas.
2.The several actual design problems have been
resolved for the applicability of the base isolation
system to the high-rise buildings.
3.Using the high strength materials and the long span
structure systems, Sendai MT building and
Thousand Tower possess not only high seismic
performance, also the flexible planning in design.
4.The recorded data of the seismographs and the
analyses show that the base isolation system acted
effectively in Sendai MT building, when the Off
-Miyagi earthquake occurred in May 26, 2003.
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Figure 17 Acceleration waves of E-W Direction
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8. REFERENCES
Ogura, K. et al, (1997), "Seismic Response
Characteristics of High-rise Buildings with Base
Isolation System", AIJ Journal of Technology and Design,
No.5, December 1997, pp.47-51
Ogura, K. et al, (1997), "Sendai MT Building", Building
Letter, October 1997, pp.1-8
Takayama, M. et al, (1995), "Ultimate Capacity of
Natural Rubber Bearings Used in Seismic Isolation
System", AIJ Journal of Technology and Design, No.1,
December 1995, pp.160-165
Kawabata, I. et al, "Structural Design of High-rise
Building with Base Isolation System Using Elastic
Sliding Bearings and Rubber Bearings", AIJ Journal of
Technology and Design, No.12, January 2001, pp.99-104