58
MODERN GASWORKS PRACTICE
and within recent years a tendency has developed to employ some system of rein-forced concrete as shown. A serviceable method of building the concrete arch.es is that of fixing in sheets of thin metal or corrugated iron, these being left in after the work is finished.
A point requiring attention is that of allowing ampie room for expansion. of the joists composing the floor; otherwise, when expansion of the benchand joists. sets in, serious stressing may result in the ultimate yielding of some portion of the structure. It is certainly preferable to arrange for independent columns some-inches from the buck-stays, the main floor girders being carried on these, so that the whole floor is completely independent of the beuch.
Owing to the continued quenching of Coke, the clinkering of fires, etc., the under portion of the steelwork where exposed is particularly liable to corrosion. An effective method of preventing this is to cover the lower webs of the joists with. cement, which. may be made to cling permanently by attaching a strip of expanded
Fig. 16.—Types or Retort-House Floors.
metal as shown in type C, Fig. 16. Another method is that of attaching a J-inch. cast-iron plate to the underside of the bottom flanges of the main joists. The plate should overlap the flange by about an inch on either side, when the joist can be concreted up solid from it.
The variation in size of retort-house floors makes it difficult to lay down more than approximate figures for their cost. In the main, however, the following may now be looked upon as average examples:—
Stage floor. Chequer plates on single joists . „ „ Double joists, concrete arches .
„ ,, Single joist, trough and concrete
„ „ For charging side, heavy maehine
6s. to Ts. M. per square foot.
9«. „ 12s.
11s. „ 13s.
13s. „ 15s. „ „ „
As the wear upon gasworks floors is somewhat considerable, it is advisable to avoid breeze and clinker in the concrete used for the floors. Where there is