9 The Quebec Bridge Collapse

October 20, 2009

At five-thirty on the afternoon of August 29, 1907, workers heard a loud retort like a canon shot. Two compression chords in the south anchor arm of the Quebec bridge had failed. The bridge was to have a span of eighteen hundred feet when completed — the longest in the world. It took 15 seconds for the bridge to collapse into the St Lawrence River. 75 workers lost their lives.

The Maths Error: Not Doing the Maths


The span of the bridge was lengthened from sixteen hundred feet to eighteen hundred feet so that bridge pillars could be built for a lower cost closer to the riverbank. In 1903 the Canadian Government provided funding and in the rush to produce drawings so that the steel for the bridge could be fabricated, there was no recomputation of assumed weights for the bridge under the revised specifications. The hierarchy ignored young engineers who expressed concern.

Failure top do the maths also caused the collapse of the West Gate Bridge in Melbourne, Australia, in 1970 killing 35 workers. In trying to connect the main lengthwise splice of the bridge, engineers started removing bolts from the main transverse splice at midspan to correct for misalignment without making appropriate calculations. They removed so many that the bridge suddenly collapsed. To this day travel speeds are controlled on the bridge to reduce the stress load and motorists believe speed limits are for road safety and not because the bridge might collapse!!!!!!!

Footnote: A new design for the Quebec bridge was with a single long cantilever span was produced. It was even heavier than the previous design. On September 11, 1916, when the central span was being raised into position, it fell into the river, killing 13 workers. (Pictured Left.)Westgate bridge  istructe.org

 Westgate Bridge Picture Left: http://www.jbrown.com.au

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