tural period of vibration of the con- ventional 31 metre building with about nine storeys is about one second, while the natural period of vibration of the Kasumigaseki Build- ing is about 5 seconds, which means the latter is more advantageous in the temblor than the former.
In short, as the predominant periods of the seismograms of El Centro earthquake (1940, U.S.A.) and others are assumed less than 1 second, the lower building may be said more dangerous, because of its tendency to make resonance (Fig. 3).
by
Though the earthquake is nature a dynamic force, it is conven- tional practice in structural calcula- tion in Japan to replace the dynamic force with the static one for con- venience sake, that is, to assume that
a certain percentage usually 20 per- cent of the building weight acting horizontally is equal to the seismic force at that point.
The strength calculation of the Kasumigaseki building was facilitated by the availability of a great number of seismograms recorded by improved seismometers such as SMAC in various places and the use of an elec- tronic computor to calculate dyna- mically the seismic forces which had been statically estimated.
In this project, seismograms such as El Centro, were repeatedly applied to the structural analysis by means of electronic computor.
The maximum acceleration of the Kanto great earthquake which hit Tokyo in 1923 was recorded at about 100 gal in the districts of good soil. The strength calculation of this build- ing was made to withstand 330 gal. which is the maximum acceleration of the El Centro waves. Therefore, the building may be said to be safe
OWNER
ARCHITECTS
GENERAL CONTRACTORS
LOCATION SITE AREA
TOTAL FLOOR AREA
TYPICAL
OPEN SPACE
HEIGHT
"
CONSTRUCTION
VERTICAL TRANSPORTATION
Elevators
Mitsui Real Estate Co. Ltd. Mitsui Real Estate Co. Ltd. Yamashita Architects & Engineering, Inc. Kajima Construction Co. Ltd. Mitsui Construction Co. Ltd. 3-4 Kasumigaseki, Chiyoda-ku, Tokyo Approximately 4 acres. 1,677,506 sq. ft.
38,111
*
72% of the site area (approx. 3 acres).
36 storeys, 485 ft. above the ground, 147 metres. Steel frame structure.
H
3
39 (Speed 150 & 300 m/min.)
2 (Speed 300 m/min.)
Passengers
Service Observatory
Garage
H
:
8
Escalators
PARKING ACCOMMODATION 500 cars, underground garage.
even if an earthquake three times greater than the Kanto earthquake should occur.
The distribution of seismic forces used conventionally for the structural design is shown in Fig. 4—k—1, but as the result of dynamic analysis, it was found that the distribution as shown in Fig. 4-k-4 is aseismatic- ally reasonable and good for making a stronger structure. This assumption of the seismic force distribution is quite drastic compared with the con- ventional one in Japan. There will be a balanced distribution to the upper floors of the shearing force acting at the base of the building.
That is to say, if the building stands on a hard soil, the base shear coefficient (the ratio of the total seis- mic force of the building to its total
weight) will get small value hyperbo- tically in proportion to the greater na- tural vibration period of the building.
On March 2, 1967, when a fairly strong earthquake shook Tokyo, the steel framework of the Kasumigaseki building was almost completed but workers in the building did not feel any shock at all. This verified the theory that the seismic influence on the building is relatively small.
Wind Resistance Design
Japan is subject to severe typhoons during summer and autumn. With conventional buildings below 31 metres high, this is not an important consideration in design because of their weight and high rigidity, but with the Kasumigaseki building, which
OFFICE
•
LANDMAN
mmci
CORRIDOR
00
CONFERENCE]
3,6 m 3,2 m
00
RECEPTION
10
• i.
SECRETARIAL
0.0
i..
EXECUTIVE OFFICES-
CORRIDOR
3.2 m
84.0 m-
3.2 m3.6 m
3.6 m3.2 m
42.4 m-
3.2 m 3.6 m
Fig. 1. Example of office layout
Far East Architect & Builder November, 1967
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