Longest Span in the World. A REMARKABLE BRIDGE

Progress, Volume II, Issue I, 1 November 1906, Page 17

Longest Span in the World. A REMARKABLE BRIDGE

One of the most remarkable bridges in the world, not only from the engineering point of view, but also from its relations as a link m transcontinental traffic will be that now under construction across the St Lawrence river about 6 miles above the city of Quebec and 170 miles below Montreal.

It will contain the longest span in the world, and will be the link that will render possible another all-Canadian tianscontinental railway. The structure, it is supposed will be built in two years. All railways will be entitled to its use. In order to avoid obstruction to ocean-going craft, the bridge is not built on a series of piers, extending across the stream, but consists technically of two great cantilevers carrying a huge central expanded span having a total length in the clear — that is, between the towers at either side — of i, BOO feet which is 90 feet longer than each of the two spans of the famous bridge over the Firth of Forth near Edinburgh Scotland 1 he approaches to the central span of the Quebec bridge are each 214 feet long extending from the shores to the supporting piers. All parts of the structure are of huge proportions, and consist mainly of built-up steel girders and other shapes, not a single casting being used The weight of each girder is 278 tons The anchor arms are <;oo feet long The bridge has a very large capacity, the floor having a total width of /sfeet It is designed to carry two lines of steam railroad, two trolley lines two carriage highways, and two sidewalks, the last-named being placed outside, and the rest of the traffic between the trusses, which are 67 feet apart, centre to centre The clear headway above water is 150 feet. It is only in recent years that the construction of such a bridge has been rendered possible, through the development in the manufacture of steel shapes The steel mills are now furnishing rolled, rectangular steel in sizes that were not obtainable at the time the Firth of Forth bridge was built. \s a consequence, the Quebec bridge is constructed with its, cantilever towers in vertical planes. It ■will have built-up lattice chords and posts and 18-inch I-beams The result will be a structure lighter in weight, cheaper m cost and the most graceful in appearance among the bridges of the world For purposes of comparison, it ma}' be interesting to note that the span of the Wilhamsbiirg suspension bridge at New York is 1,600 feet , that of the famous Brooklyn Bridge, 1,595 feet , and that of the new Manhattan bridge, 1,470 feet.