November_1967 — Page 19

In the early stage of design, a pro- blem was that, as H-shape steel has different sectional performances in X- and Y-axis as its characteristics, the size of H-shape steel subjected to seismic force is decided by the weaker sectional property, resulting in the need for a greater quantity of steel.

In order to make up for this de- fect, a layer of two beams, the so- called double beam, was set in the girder direction to balance the sec- tional properties of the H-shape steel. Through this device, the material cost of steel was reduced and columnless office space of about 16 metres span was realized.

The largest size of H-shape steel specially produced for the construc- tion of the Kasumigaseki building is 478 x 428 x 40/60 (Fig. 5.), which at the time was the largest ever made for a building element in Japan.

Figure 6 summarizes the results of study on structural design. The column type in No. 1 plan was finally adopted. Columns are set at every 3.2 m distance in the girder direction, as shown in Fig. 1.

Columns in No. 2 plan are built-up in crossed section and set at every 9.6 m distance. These two plans show the space with a long span of 16 m approximately on both sides of the 11.2 m span core.

Type of Column

Span

No. 1 H

No. 2

16”—11”—16" 16"-11".

No. 3 O

-16m

9.6" X 9.6m

Spec.

Main Member Column

H Type

Column

Cross Type Built up

Box Type

Built up

Ratio of Steel Usage

(Index)

1.00

1.03

0.87

1.60

1.25

1.16

1.10

Ratio of No. of works

at the site

Ratio of cost per ton

1.00

1.00

Fig. 6. Efficiency table of applied main member materials

In No. 3 columns of built-up box- shape section are set in a grid work of 9.6 m x 9.6 m. Though the steel quantity of No. 3 is the smallest, its total cost was finally found to be about 10 per cent over that of No. 1. No. 1 and No. 2 presented column- less space for offices, as compared with No. 3.

Conclusion

The aim to achieve high produc- tivity in construction influenced the choice of H-shape steel as well as many of the other elements used in the Kasumigaseki Building.

For example, in the fireproofing the

time-consuming method of applying asbestos by spraying was discarded in favour of the use of precast, factory- made asbestos plates.

The design of the details was also carried out with a view to high pro- ductivity for such things as slabs, par- tition walls, pipes and ducts, ceiling illumination, and prefabricated smoke chimney.

Cost reduction plays an important part in the design of a rental office building. Some remarkable achieve- ments have been made in this field on the Kasumigaseki Building, while at the same time a building with a high standard of comfort and func- tionalism has been produced.

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Far East Architect & Builder November, 1967

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