Engineering Wonders of the World
Volume I

298 ENGINEERING WONDERS OF THE WORLD. Fig. 13.—AN AIR-LOCK AT THE TOP OF ONE OF THE EIGHT CYLINDERS SUNK FOR THE FOUNDA- TIONS OF THE SOUTH TOWER OF THE RUNCORN TRANSPORTER BRIDGE. do not present any special difficulties. In building the superstructure, the electric crane used in the French bridges and at Newport was very useful. It was of light construction, and was easily raised as the work proceeded, so that the working cost per ton of material lifted came out very low. The method adopted at Widnes was different. There a steel stallage was erected between the towers, and a steam crane with a long movable jib was erected on the top, the lift being sufficient to fix the cupolas on the top of the towers. Electric power would have been used in preference to steam had it been available on either side of the river. The construction of cables is a matter on which opinions differ. In most of the French transporter bridges the main suspen- sion cable is independent of (he backstays. This is theo- retically correct, for unless the backstays and. the main cable leave the tower at the same angle, the stress in the backstays is greater than in the cable, and consequently the backstays should have a larger section. This arrangement requires, however, many more connections and adjust- ments, which may counterbalance any advan- Points about Cables. tage of cost gained by reducing the section of the main cable. The French cables are compounded of a number of ropes, the advantages claimed being facility in replacing the cables and inter- changeability ; but as the cables, if properly maintained, will last considerably longer than the rest of the structure, the necessity for interchanging should not occur. Again, the numerous cables expose considerably more area to the atmosphere than a single cable of the same gross section, and in an atmosphere laden with chemical fumes such as exist at Widnes this is an important consideration. In erecting the cables there is no advantage in having a number of smaller cables, be- cause a single cable is formed by hauling up a single strand at a time and binding all the strands Erecting ... , t . Cables. with strong steel clips. At Widnes a “ Blondin ” rope was stretched across first, upon which ran “ carriers,” to which the strands of the main cables were attached, one at a time, to be hauled into position by means of a steam winding engine. The nineteen strands making up the cable were carefully adjusted to the correct curve, and then firmly bound together. When the cables of the Runcorn Bridge were ready to receive Fig. 14.—ONE OF THE SADDLES TO CARRY THE CABLES OF THE RUNCORN TRANSPORTER BRIDGE.