On This Day: The world’s longest cantilever bridge opens – after collapsing TWICE during construction

DECEMBER 4, 1919: The world’s longest – and unluckiest – cantilever bridge was opened on this day in 1919 after collapsing twice during construction.

The 0.6 mile–long Quebec Bridge, which spans the Saint Lawrence River in Canada, cost the lives of 89 workers and took 15 years to complete.

The £5million structure, which connects Quebec City to Levis, first collapsed in 1907 and then again in 1916.

A silent British Pathé newsreel shows Prince Edward, who in 1936 became the short-reigning King Edward VIII, opening the hitherto ill-fated structure in 1919.

Luckily, the bridge - the world’s longest in all categories until 1929 - outlasted his 326 days as sovereign of the then British Empire and dominions such as Canada.

It continues to operate as a pedestrian, rail and road crossing with 30,000 vehicles using it daily - and it remains the longest cantilever structure anywhere on earth.

The initial design failed because American architects got the calculations wrong and the bridge could not support itself.

As it neared completion in 1907, local engineers working on the project noticed the steel trusses had begun twisting.

The Phoenix Bridge Company initially suggested that the beams must have been bent before being installed.

Eventually, chief architect Theodore Cooper realised his mistake and sent a telegraph reading: “Add no more load to bridge till after due consideration of facts.” 

But it did not reach the site office in time and on the afternoon of August 29, 1907, the south arm and part of the central section of the bridge collapsed.

Within 15 seconds, most of crossing plunged into the Saint Lawrence and killed 75 of the 86 men working on the bridge that day.

They included 33 Mohawks, native Canadians who were often employed in building North American bridges and tall skyscrapers due to their renowned fearlessness.

Building did not begin on another crossing for six more years until the Canadian Federal Government had hired three new architects.

Among them was Maurice Fitzmaurice, a renowned Irish civil engineer who built Scotland’s Forth Bridge, Egypt’s Aswan Dam and three river tunnels in London.

Their joint design was, like before, for a cantilever bridge, a structure of steel grid boxes ballanced on peers, in this case two.

But this second time around, the 1,800ft central span was to be much longer.

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Sadly, when being hoisted into position on September 11, 1916, the structure fell into the river – where it
still lies at the bottom - and killed 13 workers.

It was later established that the lifting procedure  - and not the bridge design nor sabotage by German agents – was at fault.

And, despite steel being in extraordinarily high demand during the First World War, engineers were immediately resupplied with new trusses and set to work again.

They completed it within three years of the second collapse.

Today, its central span is the longest cantiliver bridge section in the world – although as an overall stucture it has been massively eclipsed by other crossings.

The current longest, the Danyang-Kunshan Grand Bridge on the Beiing to Shanghai High-Speed Railway, spans an astonishing 102 miles over the Yangtze River Delta.

Within the last decade, China has built seven of the world’s top ten longest bridges following an unprecedented construction boom.

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The Quebec Bridge – or Pont de Quebec as the mostly French-speaking locals call it – remains the easternmost crossing of the Saint Lawrence, an important trade river linking the Atlantic Ocean with the Great Lakes.

But just yards to the west now lies another crossing, the Pierre Laport Suspension Bridge, which was built in 1970 to accommodate exclusively motorway traffic.