The Quebec Bridge | Pont de Québec collapsed for a second time September 11, 1916. 

There was a noise like the snapping of steel. The centre span seemed to buckle in the middle and roll over, twisting the great steel girders. Then it disappeared. There was a roaring, grinding sound when it collapsed. The giant arms and the steel bands which held the span shook considerably.” A Bridge With Two Tragedies – Legion Magazine

Quebec Bridge 
This stamp is part of a large series of stamps released 1928-1929 that included the iconic Blue Nose and Canada’s first airmail stamp Allegory of Flight.
Issued 1929 by the Canadian post office
Herman Herbert Schwartz designed the series. He was Canada’s premiere stamp designer and created some of Canada’s most well known stamps.
You can read more about him here Herman Herbert Schwartz (1885-1962) brilliant Canadian stamp designer. 
Silas Robertson engraved the issue. He and Schwartz teamed on a number of famous stamps throughout their careers.

The first catastrophic failure happened August 29, 1907, killing 76 workers. including 33 members from one Kahnawake Mohawk community. After consultations with engineers corrected design flaws, construction resumed in 1913.  Two spans were built out from each side of the river. When they were completed, the middle span was constructed a few miles way and was to be hoisted into place as a complete section. River tugs towed the completed 5,100-ton middle span 3 1/2 miles from Sillery Cove to the middle of the bridge. 

The suspended span of this bridge was assembled on shore, floated out to the center of the river, then lifted into place on the bridge. Because the suspended span was fabricated off site and moved into place on the bridge, it is considered a fabricated part of the bridge, and as such it constituted the largest fabricated metal part ever constructed in the history of the world to that date. Special mooring trusses that looked essentially like pony truss bridges hanging vertically from the cantilever arms were used in conjunction with other mechanical and structural equipment to hoist the bridge into place.
Pont de Québec (Quebec Bridge) – HistoricBridges.org

Once in position, 80 workers patiently lifted the middle span 2 feet at a time until it was in place and bolted in. Each corner was hoisted, set and then they moved onto the next corner. The process was repeated over and over, as the bridge slowly began to come together. A huge crowd of 100,000 spectators gathered on the river banks to watch the impressive engineering feat. Among those in the crowd was former Prime Minister Wilfrid Laurier and the Premier of Quebec Lomer Gouin.

“A cry of anguish went up from the onlookers as the span rushed to its watery bed,” 
A Bridge With Two Tragedies – Legion Magazine

At approximately 10:50 in the morning something went disastrously wrong on the southwest corner of the span. At first it began to sag and pull down towards the river. As the weight of the section fell further, it dislodged the other corners from their pinnings and the entire section crashed into the water, taking 13 men to their deaths. 

It was eventually determined that the load bearing jacks failed under the weight stress. The bridge was finally completed in 1917 and officially opened in 1919 when the First World War ended.