Engineering Wonders of the World
Volume I

268 ENGINEERING WONDERS OF THE WORLD. Fig. 16.—THE FINISHED FOOTBRIDGE, HELD DOäVn AGAINST WIND PRESSURE BY STAY ROPES. along the ropes from the tower tops, riding on wooden platforms hung from small wheels running on the ropes, they laid timber after timber, clamping each to the ropes, and finally- nailed down the floor boarding. The floor once laid, and guarded by hand-railings, and the finished footbridge anchored down against any lifting action of the wind, there was a thoroughly safe pathway, which even a lay- man of reasonable climbing abilities might traverse without risk. More apparatus was needed before the real cable work could be begun. On the line of each cable an endless rope was _ . _ carried across the footbridge Equipment. & and looped over pulleys on the towers so as to hang six or eight feet above the footpath. At either anchorage this rope was strung round a large horizontal wheel. By turning these wheels with, electric motors, the rope, called the “ travelling rope,” would act like an endless belt, one side moving from Brooklyn to Manhattan, while the other moved in the reverse direction. At two points on the travelling rope there were attached light frames, each carrying a vertical pulley or sheave. These travelling sheaves were, of course, moved across the span in either direction by the motion of the rope ; they did all the real work of cable-spinning. The wire for the cables was brought to the work on large reels, 5 or 6 feet in diameter, each reel carrying many miles of wire. As about 160 miles of wire was ultimately joined in a continuous length to make one of the thirty-seven strands of a cable, we have a total of about 24,000 miles for the four cables, nearly sufficient to girdle the earth. At all times several such reels were on either anchorage, whence the work trolled. To serve as pattern or guide for wires, one length, of wire was strung across the span over temporary supports slightly above the line of the finished cable, and ad- justed very accurately to the exact curve desired. This was the “ guidfe wire.” To begin the spinning, one end of a reel was fastened to a “ strand-shoe,” a block linked to the chain of Then the wire was partly un- reeled, passed forward, and looped around the travelling sheave. The motor was now started, moving the travelling rope and carrying the sheave slowly upward from anchorage to tower, and thence over the entire span to the opposite anchorage. In travelling along, the sheave paid out that end of the wire which had been fastened to the strand-shoe (the “ dead wire ”), and at the same time, drawing out wire from the reel, pulled this second pass of wire (the “ live wire ”) also across the hand at was con- the cable curved steel anchor bars. Cable- spinning.