Engineering Wonders of the World
Volume III

THE ARCH BRIDGES OF NIAGARA FALLS. 283 girders, 190 and 210 feet long, on the New York and Canadian sides respectively. The arch has two parabolic braced ribs, about 26 feet deep, divided into twenty main panels 42 feet long. From the top of each of the main panel points vertical Details of latticed posts extend to the Bridge. floor of the bridge, which they support. At the skewbacks the ribs are 681 feet apart, centre to centre ; at the middle of the arch, 30 feet apart. The hinges at the skewbacks, which take the entire weight of the arch, are pins 5 feet long and 12 inches in diameter. The floor of the bridge is 46 feet 3 inches wide, divided longitudinally into two outer side-walks, 3 feet 9 inches wide each, a central double trolley car track, 22 feet 9 inches wide ; and two 8-foot carriage ways be- tween car tracks and side-walks. Mr. L. L. Clauses in Contract Specification. Buck was engineer in charge of the construc- tion of this bridge also. Some of the clauses in the specification furnished to the contractors, the Pencoyd Iron Works, may be of interest to the layman, as showing what conditions are exacted in work of this kind :— “ Rivets must completely fill their holes. “No rivet driven either by hand or machine may be caulked or recupped. “ Before final assembling for riveting, all surfaces which will be inaccessible afterwards must receive a thorough coat of red-lead paint. “All sheared edges must have a 1-inch of material removed by planer afterwards. “ Pin holes must be bored accurately to a * diameter of sV-inch larger than the pins they are to receive. “ All pin holes must be smooth and accu- rately bored. “ Loops in iron rods must be so welded that the weld shall be strong enough to break the body of the rod.” A difficulty that the engineers had to face was that the centre line of the new bridge did not coincide with, or run parallel to, that of the old bridge. At the Canadian end they met ; at difficulties to be overcome. the other they were nearly 17 feet apart, the new bridge being south of the old. This was due to the Cataract Construc- tion Company’s discharge tunned having its outlet at the point where otherwise the New York skewbacks would have been placed. Another difficulty lay in the fact that the north rib of the arch would strike the bottom chord of the north stiffening truss of the sus- pension bridge about 100 feet from the centre. This necessitated the reinforcing of the top half of the trusses, so that, when the time should arrive, the bottom half might be cut away without rendering the trusses useless. The plan adopted for the construction oi the arch was as follows : To start the arch in such a manner that at a temperature of G0° Fahrenheit the bottom chords of the arch should meet ex- Plan for actly, and be pinned tem- the porarily, to form a three- hinged arch. (The other two hinges would, of course, be at the skewbacks.) The top chords of the two panels nearest the centre, hitherto omitted, would then be finished, and subjected to pressure to impart the due amount of stress while they were joined up, so converting the structure into a two-hinged arch. The anchorages for the bars which would take the weight of the cantilevers during erec- tion were sunk in pits of such depth that the weight of rock above would of itself suffice to counteract the Anchorages n e ! . , ,. and Anchorage pull of the completed canti- Bars levers. Next to an anchorage came a toggle joint, to the outer end of which was attached the first of the anchor links run- ning to the top of the first post. To support a cantilever and distribute the strains prop- erly, secondary anchorage bars ran from the top of the first post to panel points 2, 4, 6,