Engineering Wonders of the World
Volume I

THE BRIDGES OF NEW YORK CITY. 261 described farther on in this chapter, we need not stop to recount the work of the Brooklyn Bridge builders. Some points in its later his- tory, however, merit our attention. Fig. 4.—TOP OF ONE OF THE BROOKLYN BRIDGE TOWERS, SHOWING THE LARGE SADDLE OVER WHICH A MAIN CABLE PASSES. The saddle rests on rollers which permit easy movement to accommodate expansion and contraction of the cable, or changes of load. From near the saddle radiate diagonal stays to the stiffening girder. It is a very interesting fact that the heavy traffic across the bridge has gradually become too great, chiefly because the ponderous rail- way and trolley cars of to-day Strengthening- were no^. anficipated forty years the Bridge. . * ago. Therefore the authorities of New York city have for some time been planning to strengthen the bridge. Highly ingenious schemes for doing this have been devised. Unfortunately, they are too intricate to be described here. Suffice it to say that the main parts of the bridge—the cables and the great stone towers—are amply strong ; the weakness is in the smaller pieces, detail parts, and connections. This is not surprising, for, as engineers well know, many structures are weakest in details, just as a garment is apt to show its first troubles at the buttons or in the seams. Fig. 5. A sensational illustration of this fact de- veloped in the Brooklyn Bridge a few years ago. On a hot summer day in 1901 several of the short suspender rods near the middle of the bridge (Fig. 5 shows tlieir position) were found to be broken through. These rods are capable of holding up some 60 to 80 tons each, but evidently they had been overworked by the to-and-fro movement of the bridge as its metal-work contracted or expanded with the temperature changes. Clearly the adja- cent rods now had to do extra duty, and there was danger that they might all tear in succes- sion, like the easy ripping of a seam after the first thread is started—a very grave danger, since the whole roadway would drop into the river. Needless to say, prompt and energetic action was taken. The roadway was fenced off on the side of the broken rods, and new rods were made and inserted. A thorough investigation subsequently showed that the bridge, sooner or later, must have a general strengthening of its small parts. Incidentally, let it be remarked that this bridge costs the city nearly half a million dollars each year merely for inspection, paint- ing, cleaning, and small repairs—a good-sized fortune. The income from the rental pay- ments of the cars which cross the bridge just about balances this annual expense. THE WILLIAMSBURGH BRIDGE. Thirteen years elapsed between the open- ing of the Brooklyn Bridge and the commence- ment of the work on the second bridge across the East River, in 1897. During this period bridge-building science had advanced so much that, whereas fourteen years were needed to construct the first bridge, the Williamsburgh Bridge took less than half that time—that is, a few months over six years. Yet it is both longer and much stronger than its older brother, being able to carry about twice as great a load per running foot of bridge (see its cross- section, Fig. 7). The two more recent bridges, it is true, have been made still stronger, but the Williamsburgh Bridge retains the honour