Engineering Wonders of the World
Volume III

THE ARCH BRIDGES with the jibs was provided for by shifting the jibs vertically. When construction had reached panel point 15 on the Canadian side, and point 17 on the New York side, it became necessary to re- move the entire floor system Interference of tjie SUSpension bridge to with Old . „ , . Bridge. glve rooni for closmg the arch. The old bridge trusses were therefore removed entirely, except the top chords, between the points mentioned, OF NIAGARA FALLS. 285 completed, a timber floor, supported by the suspension cables, was built across the gap, and road traffic was resumed after an inter- ruption of but four days. Construction was greatly hampered at this period by rain and by very high winds, which deposited the icy mist from the Falls on the steel work and Climatic ropes, making work very dan- gerous for the men. No accident of any kind occurred, however, and in due course the clo- DIAGRAM TO SHOW METHOD OF ANCHORING THE CANTILEVERS OF THE NIAGARA FALLS AND CLIFTON ARCH DURING CONSTRUCTION. The dotted lines indicate the anchorage bars carried from the top of Bent No. 0 to Panel points 2, 4, 6, 8, 10, 12, 14, to support the cantilever until closure with its fellow. The adjustable toggle and anchorage are represented on a greatly exaggerated scale. and erection proceeded as usual. The north rib of the arch rose between the two cables of the old bridge, and the south rib some distance outside. As the south cable was in line with the two top chords of the arch, the horizontal cross bracing between the top chords could not be added at once, and its place was taken by temporary timber struts resting against the lower chords. On April 17, 1897, the lower chords of the two cantilevers met, and with such precision that the pull exerted by an ordinary hand winch sufficed to draw the eyes into the exact posi- tion which, allowed the driving of the great centre pins. The closure of the bottom chords sure of the top chords was effected with the aid of hydraulic rams. After the adjustment of the arch had been completed, the joints of the chords were all examined, and found to be absolutely perfect, no packing between Exactitude in Calculation. bearing surfaces or reaming of rivet holes being required. The results attained indicated an exactness of calculation, field measure- ments, and shop work rarely if ever equalled.* After the final closure the anchorage bars were removed, and the vertical bents to sup- port the roadway erected wherever the trusses of the old bridge permitted. Then com- * Engineering.