The plan given in Fig. 235 is that of an important building carried out entirely, as far as its interior proportions are concerned, in armoured concrete, the outer walls alone being of brick.

The building, designed by Messrs. Tunbridge & Tunbridge, consists of six storeys and a basement with a flat roof above, which is used for offices and residential flats.

The general principle of construction is that of the erection of a series of double vertical columns flanking the centre corridor, supporting longitudinal girders, which in turn support transverse girders receiving the floors and partitions. The method of construction consists first in the placing in position of a network of commercial round bars (no twisted or deformed bars employed), steel being preferred in some cases, although reinforced members wholly in tension have iron freely used in them.

In the proportioning of reinforcements more than usual attention was paid to adhesive stresses as distinguished from direct tensile stresses. For this reason the bars used were in large numbers of small diameter, no bars even in the heaviest girders being greater than 1 1/4-inch diameter.

The standard proportions of concrete used for all members subject to cross bending was one part of Australian Portland cement, two parts of sand, and three or four parts of basaltic screenings from 1/2 to 3/4-inch gauge. The concrete was invariably mixed as a " very wet " mixture, being of such a liquid consistency as tobe freely poured, and requiring very little ramming for its complete consolidation.

The building has plan dimensions of 80 by 37 feet.

The whole of the supporting girders and joists, the columns and their footings, the stairways, the safes, the lintels, and the whole of the interior walls are one monolithic mass of concrete scientifically reinforced in every direction, of which a detail is given in Fig. 236. The floors are but 3 inches thick, and the interior walls only 2 1/2 inches, thus providing a building which, while in a high degree fireproof, is constructed of imperishable materials of great rigidity, vermin proof, and most economic of space.

Upon the temporary wood casings being removed it was found that the surfaces were so smooth as to render but little surface plastering necessary, a thin coat of American rock wall plaster being used.

The floors are laid with heavy linoleum secured with mastic to the concrete surfaces.

Other important works are now in course of erection in this manner in various parts of Australia, and the armoured concrete has found much favour in engineering works.

Armoured Concrete 295

Fig. 236.