Engineering Wonders of the World
Volume I

292 ENGINEERING WONDERS OF THE WORLD. Fig. 7.-NANTES TRANSPORTER BRIDGE. FLOATING THE CENTRAL GIRDER. were sunk by means of compressed air, and contain each about 19,500 cubic feet of masonry and concrete. The cost of the bridge was about £70,000. The bridges previously described are all of one type, each having a stiffening girder sus- pended from steel cables, and towers hinged at the base ; but as it is not always possible to obtain space for the great masonry an- chorages, the above designs sometimes have to be modified. In the year 1902 a bridge was commenced at Nantes by Monsieur F. Arnodin, and com- pleted in the following year. Its span is 465 feet between the centres of the towers, and it clears the water by 165 feet. The design of this bridge differs from those already described in the method of carrying the main girders. As seen in our illustrations (Figs. 7, 8, and 9), each of these girders is subdivided into three parts, of which two are suspended directly from the tower by raked cables. The outer ends, projecting 83 feet The Nantes Bridge. landwards, are anchored vertically to the ground. The 113|-foot space between these cantilever girders is spanned by a central girder, raised into position when its two sup- ports had been completed. The cantilever principle facilitated erection greatly, and was subsequently employed for a transporter bridge of 545-foot span built at Marseilles. Another form of transporter bridge is that designed by Mr. C. A. P. Turner for crossing the ship canal at Duluth, Minnesota. This design is entirely different from the French bridges : the towers are fixed at the bases, and the towers and girders combined form one rigid structure. The main girders are 54 feet deep at the centre, anti 30 feet deep at the ends. The clear span is 393 feet 9 inches ; the clear headway from surface of canal to under side of girders 135 feet. Like the towers and girders, the car suspenders also are rigid, and not attached to the trolley frame by means of wire suspenders. The trolley is electrically driven by rope gearing in a manner some- what similar to that used for the other