A Treatise On The Principles And Practice Of Dock Engineering

454 DOCK ENGINEERING. 1 lie decking is of greenheart, laid upon a 4-inch platform of creosoted pine. Under the wheel tracks, which are iron-plated, the greenheart is laid in longitudinal planks, 4 inches thick. The horse tracks, 3 teet wide, are of blocks, 9 inches by 5 inches by 3^ inches, set in Portland cement. Ihe footpaths are of 3-inch greenheart planks, laid longitudinally across 4J-inch by 41-inch bearers. There are elm rubbers, 9’ inches by 5j inches, at each side of the bridge. The handrail, which adjoins the waterway when the passage is open, is arranged to fall, so as to offer no obstruction to warps and lines. While the passage is in use the bridge remains upon its pivot, but, having been rotated across to the closed position, a couple of vertical cast- iron rams, working in a 25-inch diameter hydraulic cylinder, with a 7 inches stroke, lift the extreme tail end of the bridge, so that the latter leaves the pivot and tilts forward on to bearing blocks at the edge of the coping on both sides of the passage. At the same time a pair of sliding blocks are brought under the tail end, and a very slight subsidence of the rams causes the bearing to be transferred to the blocks. The slewing inachinery consists of a pair of hydraulic rams, each 14 inches diameter, 9 feet 10 inches stroke, and furnished with sheaves giving a power of 2 to 1. The roller path is 43 feet radius and the wheels are of cast steel, 17 inches diameter, turned, bored, and coned. The slewing chain is 1g- inches diameter. The radius of the slewing drum is 11 feet 9 inches. The Victoria Swing Bridge at Leith.* This bridge (fig. 444) constructed in 1874 lias a clear spån of 120 feet and was, at the time of its construction, the largest in tlie kingdom. The total length is 214 feet 3 inches, and the width over all, 39 feet 3 inches. The platform comprises two lines of railway and roadway, with a footpath on each side. The weight of the whole bridge is upwards of 600 tons, including a counterpoise of 240 tons. There are two main girders, each 27 feet in depth. The pivot or lifting press has a diameter of 5 feet 9 inches, and divides the bridge into a long arm of 147 feet and a short arm of 67 feet 3 inches. The principle upon which the bridge is manæuvred is the same as that described in connection with the Marseilles bridge, with the exception that the ordinary hydraulic pressure of 750 Ibs. per square inch serves to work the pivot without the intervention of a force pump. The turning gear is illustrated in fig. 445. Swing Bridge at Stanley Deck, Liverpool.! This bridge carries an overhead electric railway across the 50-foot entrance to the Stanley Dock. It is a combination of a swing bridge and a * Whyte, “ Notes on Leith Docks and New Works in Progress,” 1901. t Greathead and Fox on “ Liverpool Overhead Railway,” Min. Proc. Inst. C.E., vol. cxvii.