Engineering Wonders of the World
Volume I

Fig. 12.—SKETCH OF THE WRAPPING AND SHEATH- ING OF ONE OF THE WILLIAMSBURGH BRIDGE CABLES. Each cable is 18^ inches in diameter. The four cables weigh together 5,000 tons and contain 19,000 miles of wire. 266 ENGINEERING WONDERS OF THE WORLD. and over this were placed tight steel shells (as sketched in Fig. 12). The object, of course, is to protect the cables perfectly from all chances of rusting. For the same purpose the spaces between the wires in each cable are filled with a thick oil or grease. This form of cable protection was a novelty. The Brooklyn Bridge has on its cables a spiral wrapping of wire, close laid and squeezed tight, and afterwards thoroughly painted. As a matter of fact, the wire wrapping has proved superior to the steel shell covering, for repeated examination of the Brooklyn Bridge cables shows complete absence of rust, whereas the Williamsburgh Bridge cables prove to be not so perfectly protected. On the Manhattan Bridge, therefore, the old plan of a spiral wrapping of wire is being used. The cables and suspenders once in place, the bridge is nearly completed, though it looks very far indeed from finished. Erecting the steel framing of the floor and stiffening trusses is commonplace work for the bridge-builder. A derrick reaches out from the tower and hangs the first floor-beam to the bottom ends of the first set of suspenders. Then the longitudinal members are placed on the support thus gained. When a section thus built out is so far com- plete as to be rigid, the derrick is moved for- ward, and the same operation is repeated until the entire floorwork is in place. Then the stiffening trusses are built up, one special precaution being taken : the material of the trusses must be brought out on the floor and distributed along the bridge in pro- portion to its final distribution, so that its weight will bring the cables to the exact curve which they are to have in the completed structure. If this precaution were neglected, the trusses could not be made straight, through being strained into a wavy shape, as the pro- gress of their erection shifts the load on the cables. The construction of the Williamsburgh Bridge was distinguished by an interesting accident. When the cables were just completed, some wooden staging on the top of ® ° r An Accident the west tower caught fire, and, being soaked with grease from the cables, it made a hot little blaze. The wire-rope foot- bridge used in the work of laying up the main cables was wrecked, because its ropes softened and tore apart just over the tower. There was great fear that the main cables had been injured by the heat, in which case the work of a year would have been nullified. An expert investigation showed, however, that only a few of the outer wires were weakened, and that the damage could be repaired. Very reassuring news! Clearing away the foot- bridge wreckage was a vexatious piece of work, of course, but it brought no difficulties, and the bridge was completed without further incident. THE MANHATTAN BRIDGE. A short distance north of the Brooklyn Bridge a third suspension bridge is being built, to relieve the old bridge of its excess traffic, and to develop new routes of transportation. This structure affords us an opportunity of studying the process of cable-spinning in the most perfect manner yet attained. First, a glance at the general characteristics and dimensions of the bridge. Its main span of 1,470 feet, and shore spans of 725 feet, are supported by four 20|-inch cables, the largest ever attempted. The 9,472 wires—each ’192 inch in diameter—are galvanized for rust