Khaled Mahmoud

Modeling of bridges

At the time of its construction, the 1800 ft span cantilever bridge across the St. Lawrence River in Quebec, Canada was going to be the longest cantilever bridge in the world. However, on August 29, 1907, during its erection, the bridge collapsed killing 75 workers. A commission of prominent international engineers was formed by the Canadian Government to investigate the collapse of the Quebec Bridge. It was decided to build a new, but much heavier and stronger, cantilever bridge adjacent to the old failed bridge. On September 11, 1916, after the center span was raised successfully 12 to 15 feet, it suddenly fell into the St. Lawrence River killing eleven workers and injuring six. The St. Lawrence Bridge Company, which was erecting it, took full responsibility for the collapse of the second bridge and placed orders for the new steel. The new center span was successfully hoisted for the third time and put in place on September 18, 1917 using the same lifting procedure that was used in 1916. The new bridge was opened to traffic 100 years ago, on December 3, 1917. This paper provides the details of the old and new bridges, and the people connected with them. Length of center (cantilever) span: 1442 ft Length of shore spans: 487 ft Total length of bridge and approaches: 3460 ft Height from high water mark to bottom of bridge: 150 ft Extreme height of top of cantilever above high water: 408 ft In this design, the center span was 270 ft shorter than the 1710 ft single cantilever span of the Forth Bridge near Edinburgh, Scotland, the world’s longest at the time. To avoid founding the two piers supporting the cantilever span in deep water, numerous borings were made which indicated that while solid rock was beyond a depth feasible to reach, suitable material for foundation could be found well within the practicable limits of pneumatic work by locating the main piers near the shores. In 1900, Theodore Cooper, the Consulting Engineer to the Quebec Bridge Co., increased the length of the cantilever span to 1800 ft which would make the Quebec Bridge the longest cantilever span in the world when completed. He approved the stress sheets for the suspended and anchor spans in 1904. One-half elevation of the Quebec Bridge symmetrical about the centerline is shown in Figure 2 after the revisions made by Cooper. The contract for the superstructure of the bridge was awarded to Phoenix Bridge Co. of Phoenixville, PA. and had an estimated weight of about 40,000 tons. The bridge was designed to carry two railroad tracks, two trolley tracks, and two roadways between the trusses on the single deck, and two sidewalks cantilevered outside the trusses. The trusses were placed 67 ft apart center to center. Mr. E.A. Hoare was Chief Engineer of the Quebec Bridge Co. Figure 1. Location 1 to build the Quebec Bridge, oriented in the north-south direction. Figure 2. Half diagram of the Quebec cantilever bridge.