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August 30, 2000
Birth of Japan's Largest Base Isolation Retrofit Work
Done "while the building is being used," without disturbing the tenants
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| Artist's impression of the completed Tokyo DIA Building base isolation
work |
Many examples of base isolation systems
can be seen in newly constructed buildings around Japan, but there are
only about 20 examples of base isolation improvement
work (*1) being done on existing buildings, mostly on cultural
assets and government buildings, but now more examples of this system
being used on hospitals and research facilities can be seen.
Takenaka Corporation (President: Toichi Takenaka; Head Office: Osaka)
is responsible for the improvement work (started in December, 1999 and
due to be completed by November, 2001) being done on Buildings 1 through
4 of Mitsubishi Logistics Corporation's "Tokyo DIA Building," a complex
housing a computer center and data storage facilities. This improvement
work is not only the largest base isolation work ever undertaken in
Japan, but it is also being done "while the building
is being used" (*2), and is unique in that it will also incorporate
some high-performance base isolation functions.
*1 Base isolation improvement
work
Improvement work changing the building structure to a base isolation
structure is done, by installing base isolation devices between the foundation
of the building and the building itself, or between mid-level floors
in a building so the energy of an earthquake doesn't affect the building
directly. When this work is done in an existing building, it is called
base isolation retrofit work.
*2 Base isolation procedure
while the building is being used
Base isolation improvement work on a building can be done either after
stopping use of the building, or while the building is being used. Base
isolation improvement work on a building while the building is being
used is an extremely effective method for strengthening and improving
a building when the owner wants to increase the safety of the building
during a major earthquake but the tenants cannot stop their day-to-day
business.
Features of the "Base Isolation Work While the Building Is Being
Used" in the Buildings 1 through 4 of the "Tokyo DIA Building"
1. The largest base isolation work ever undertaken
in Japan, joining four buildings into one (see attachment 1)
With this work being done on Buildings 1 through 4, it is the first
time that base isolation work is being tried joining a number of buildings,
using 264 rubber bearings, 28 wall-type viscous dampers over an area
of about 68,000m2. This work is not only the largest base isolation
retrofit work, but also larger than any work ever done on a new building.
2. Base isolation work undertaken while computers
inside the buildings were operating 24 hours a day
The "Tokyo DIA Building" houses many host computers and servers that
continue to operate 24 hours a day. The base isolation work is being
carried out on the foundations under the first basement floor "while
the building is being used" without disturbing operations going on in
the buildings. During the work, temporary strengthening is installed
to give the building additional earthquake resistance. At the same time great care
is taken not to affect the equipment and facilities housed inside the
building.
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3. High-performance
base isolation functions
The response acceleration (gal) in the event of an earthquake the size
of the Great Kanto Earthquake would be about 400gal in the underground
foundation area, would increase the higher up the building you went, and
on the 11th floor would be about twice as much, or about 800gal. In this
project, the owner of the building has asked that the response acceleration
be kept to under 200gal at the floor level of each floor, so high-performance
type base isolation devices such as rubber bearings to limit the transmission
of the earthquake motion to the building, and wall-type viscous dampers
to reduce the earthquake energy have been used. As a result, it is possible
to keep the shaking of the building to under 100gal.
Procedure of the "Base Isolation Work While the Building Is Being
Used"
Buildings 1 through 4 of the "Tokyo DIA Building" complex are first joined
together at their foundations, and the buildings are supported by the
installation of braces and temporary supports. By doing so, the buildings
are given more earthquake resistance during the work than beforehand,
and then the piles are cut and the rubber bearings installed. 264 rubber
bearings are installed, after which 28 wall-type viscous dampers are also
installed, giving the entire complex high-performance base isolation.
- Struts are installed after earth-retaining walls are set up. Excavation
work is carried out at the periphery of the building, and then under
the building after retaining walls have been installed.
- Steel piles are pressed in, and mat slabs are installed.
- Temporary strengthening is installed to give the building additional
earthquake-resistance while the work is being carried out.
- Temporary staging is installed to support the building, and the
piles are then cut.
- Rubber bearings are installed into the cutout area of the piles,
and fixed in place using concrete.
- Wall-type viscous dampers are installed.
- The struts and temporary strengthening are removed, and the base
isolation work is complete.
At Takenaka, as well as being able to undertake base
isolation work for new buildings, a large menu for base isolation work
to be applied to existing buildings has also been developed. Takenaka
can recommend the best method, including the best floor for installation
of the base isolation system and the type of base isolation system, according
to the location, size and use of a building.
Attachment 1
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