Engineering Wonders of the World
Volume I

THE BRIDGES OF NEW YORK CITY. 271 Until the Queensboro Bridge was com- pleted, the longest cantilever in America was the 812-foot span of the Monongahela River Bridge of the Wabash Railway at Pittsburg, Pa. Later a vastly bolder attempt was made at Quebec, where an 1,800-foot cantilever was begun in 1904; but even before comple- tion this structure collapsed on August 29, 1907, carrying down eighty workmen to death. The Quebec Bridge would have outranked the famous Forth Bridge by nearly a hundred feet. The Queensboro Bridge is much smaller. The two channel spans are unequal. The west or Manhattan span, the longer, measures 1,182 feet ; while the east or Queensboro span is only 984 feet. Adding the 630-foot connecting span over Blackwell’s Island and the shore arms of 469 feet and 459 feet, we find the bridge to have a total length of 3,724 feet, nearly three-quarters of a mile, not counting the extensive approaches. The other dimensions of the structure are correspondingly large. The roadway is over- . topped nearly 200 feet by the high posts over the piers. Two massive floors, 86 feet wide, afford room for four railway tracks, four trolley tracks, two Fig. 22.—Blackwell’s island bridge, island span, SHOWING FALSEWORK, AND THE TWO GREAT “ TRAV- ELLERS ” FOR HANDLING THE PARTS. Fig. 21.—HANGING THE SUSPENDER ROPES FROM THE FINISHED CABLES, MANHATTAN BRIDGE. The footbridges are at this stage still needed for wrapping the cables, but they have now been hung directly to the main cables, and their rope supports have been cut up to uso as suspender ropes. footwalks, and a carriage-way, equivalent to the space of a street 170 feet wide. Because of this immensely heavy load- ing, the bridge contains pieces which are about twice as strong as any bridge members ever before built, even including the Quebec Bridge. In fact, its heaviest strut or compression member is equal to a solid rectangular bar of steel two feet thick and four feet wide ! As to the principle embodied in the cantilever type of bridge, we may under- stand it by looking at Fig. 23. That part of the structure which rests on the two island piers is virtually a large horizontal beam, resting on the two piers and jutting out 500 to 600 feet