Engineering Wonders of the World
Volume III

THE ARCH BRIDGES OF NIAGARA FALLS. 281 RAILWAY ARCH BRIDGE, SHOWING CONSTRUCTION AS ON MARCH 16; 1897. In the background is the cantilever bridge of the Michigan Central Railroad. place the pedestals of the skewbacks at the points of support of the arch. Each pedestal was a casting weighing 23 tons, so that the task of getting it on to its masonry founda- tions and aligning it with the exactitude neces- sary to ensure the accuracy of the closing of the arch was not an easy one. The impossi- bility of erecting any support in mid-stream made it necessary to build out the arch as two cantilevers from each bank to a point of meeting. To give proper support for the cantilevers, four holes were Anchorages. excavated in the solid rock to receive large steel grillages filled in with con- crete. These grillages took the strain of four sets of anchor chains running to the tops of the first bents or uprights of the cantilever. Each chain was composed of such of the eye bars and top chord sections of the 115-foot spans as could safely be used for the purpose, and of odd members of suitable shape and strength. The designer included in each chain a toggle , or diamond-shaped frame, hinged at each corner, with its longer diameter lying in the direction of the chain. The outer end was attached to Adjustment TOffffleS. the chain, the inner to the anchorage. Through the top and bottom hinges passed a right- and left-handed screw, 17 feet long and 9| inches in diameter, furnished with a capstan, the turning of which would alter the shape, and consequently the length, of the toggle, and move any weight supported by the chain. (See diagram on page 285.) This device made it an easy matter to adjust the positions of the canti- levers exactly when the time came to join up the arch. Twelve men at each of the two capstans sufficed to lower a cantilever, and double that number was required to raise it, the complete cantilever weighing about 500 tons. The toggles proved an entire success. Thanks to the care with which the