Modern Gasworks Practice

THE STORAGE OF GAS 679 between old and new work water-tight, a reinforced concrete apron, 17 indies thick and 6 feet 6 inches deep, was placed round the outside of the old tank and connected monolithically with the ring of reinforced concrete, 15 inches thick, which was built directly on top of the stone coping of the old tank. The walls of the tank were then carried up monolithically to a height of 10 feet. The reinforced concrete is 9 inches thick at the bottom and 6 inches thick at the top, the reinforcemeut (see Fig. 421) consisting of rib bars varying from 1 inch diameter at 6 inches centres at the bottom to l-inch bars at 7 inches centres at the top. On the top of the tank a reinforced concrete platform, 2 feet 6 inches wide and 3 inches thick, was cantilevered off the wall. To carry the gasholder guide-framing standards twelve reinforced concrete piers were built monolithically with the tank ; and, owing to the treacherous nature of the ground, the piers were supported on heavily reinforced concrete can-tilevers, bearing on the old brick wall and tailed down by the entire weight of the reinforced concrete tank. When fmished the interior of the tank was rendered with a |-inch. layer of 2 to 1 cement rendering. Steel Tanks It may be laid down as a general rule that unless a gasholder is upwards of two million cubic feet capacity a steel tank is undoubtedly the most economical. In modern practice the steel tank finds considerable favour in all cases except where the holder is of any great size, although steel was employed for a ten million holder tank at New York, which has a diameter of 250 feet and a depth of 46 feet. Steel tanks may be said to possess the folio wing advantages :— (a) They are usually less expensive than masonry tanks. (b) A foundation which might be classed as unsuitable for a sunk tank may be sufficiently stable for a steel tank. (c) Quickness and ease of construction. (d) Owing to the ease of determining the working stresses with reasonable accuracy there is no difficulty in designing the tank with a knowii factor of safety. (e) Steel is reliable under stress. The properties of brickwork and concrete in this direction are uncertain. (f) The tank can be readily tested and made water-tight, for the whole is acces-sible for inspection. As regards the floor plating, it is usual to put the sections together on bearers which raise it a short distance above the foundation. When the floor, bottom curb and bottom row are riveted up, the tank is filled with water to a depth of about one foot. Any joint “ weeps ” are then attended to and the whole is afterwards let down on to its foundation. (<?) Masonry tanks must be allowed to stand for some time after completion before they are filled with water. The steel tank may be filled immediately it is finished. (li ) With the steel tank there is no initial stressing caused by shrinkage or change of temperature. (i) The failure of a steel tank is extremely rare. On the otter hånd, the advocates of the masonry tank point out that:—