Engineering Wonders of the World
Volume III

THE ARCH BRIDGES OF NIAGARA FALLS. 287 menced the laying of the steel floor system, this part of the work being conducted from the centre outwards. Openings were left in the floor for the south suspension cables, which were not removed until the bridge had been completed except for the filling-in of these openings. In short, the floor system was built round the cables. While the floor was laid between panel points 18 on each side of the centre, the bridge had to be closed to traffic for one day. During the rest of this part of the construction two movable bridges were used, and shifted along to span the gaps between the completed arch flooring and that of the suspension bridge, as lengths of the latter were demolished to make room for the steelwork. The building of the arch itself occupied but thirty-two working days, and the erection of the 2,200 tons of steelwork was completed in less than six months—a remarkable achievement, considering the difficulties to be overcome. During January of 1899 ice came from the Falls in great quantities, and piled up in the gorge to a height of 25 feet above water. The ice - field, firmly anchored to both shores, gradually thick- ^ce ^am ened downwards, and choked Results. the waterway, so causing the water to rise until it flowed over the ice. The increased hydrostatic pressure broke the jam. The ice swept down the gorge to the masonry abutments of the new bridge, rose above them, and struck the steelwork of the ribs, by which it was shaved away quite cleanly. The bridge quivered from end to end, but did not sway. After the ice had passed, and an examination of the bridge was possible, the damage was found to be confined to the bend- ing of four members, which were straightened immediately. During the next summer, as a precaution against future troubles of the same kind, heavy concrete walls were built round the abutments. [Note.—For the photographic illustrations of the Grand Trunk Railway Bridge which accompany this article, we are indebted to the Pennsylvania Steel Company.]