Looking today at the imposing bulk of Quebec Bridge as it straddles the St Lawrence River, you would be hard pushed to imagine its inauspicious origins. The crossing of the mighty St Lawrence was always going to be a major engineering challenge, but by the beginning of the 20th century a solution to the efficient transport of goods to the city on the north bank had become imperative. The design of the prestigious project was entrusted to one of America’s most eminent bridge builders, Theodore Cooper. The site, to the west of the city, would not only mark the easternmost crossing of the river but would also have to allow the passage of large ocean-going vessels.
Cooper produced a design for a steel cantilever bridge with a single central span 46 m (150 ft) above the water. In order to reduce costs the original dimensions were altered, producing a central span with an unparalleled width of 549 m (1,800 ft). This modification fatally compromised the integrity of the design. When work on the bridge began in 1904 Cooper was old and infirm; he relied on reports from his engineers, sent to his New York office.
In August 1907 the south cantilever was already projecting 230 m (750 ft) from the pier when buckling was noticed on some steel plates. Cooper’s instructions to suspend construction pending investigation failed to reach the builders and on August 29 the whole structure collapsed, taking with it 85 men. Even though the replacement structure used two-and-a-half times as much steel, it too ran into difficulty. Nine years later the new central section was being raised carefully into position between the cantilevered arms when a rupture caused it to crash into the water.
When: August 29 1907 and September 11 1916
Where: St. Lawrence River, Quebec, Canada
Death toll: 74 (1907) and 11 (1916)
You should know: Quebec Bridge finally opened in December 1917 and has stood without incident since. It is still the world’s longest single-span cantilever bridge.