Introduction
The Quebec Bridge, located in Quebec, Canada, across the St. Lawrence River was the largest cantilever bridge in the world. It collapsed twice, once in 1907 and again in 1916, with 89 worker deaths resulting from the two occurrences. It was built by the Quebec Bridge Company, eager to find a way to allow for year-long trade across the river, which included the Quebec bridge committee, a team of businessmen and political leaders eager to move along the project, along with the president and several chief engineers for the Phoenix Bridge Company. This disaster was primarily due to a flaw in the design, specifically in the latticing of the compression cords. The dead load was not recalculated when the bridge’s length was extended, ultimately leading to very high allowable stress and a buckling failure for Chord A9L and R.
One of the major equations that played a factor in this disaster is the formula for normal stress: stress = Force / Area. In the case of the bridge, the allowable stress calculation was what ultimately led to its demise, since they expanded the bridge and therefore the cross-sectional area, causing the allowable stress to decrease that can withstand the same load that would have originally been applied to the bridge. Therefore, the limit that was exceeded was the stress, causing the bridge to extend past its elasticity point and snap, leading to a bridge failure.
From an engineering perspective, one of the big takeaways from this is how much the strength of the material and the amount of allowable stress before reaching the breaking point depends on the measurements of the material itself and the distance the load was applied over. Since the length was extended, the material itself was less sturdy and could hold a smaller amount of weight, which had not been accounted for by the engineers on the team. Therefore, it was created with a larger amount of tension applied which was ultimately too great for it to withstand, causing it to break.
In terms of my personal perspective, one of the lessons I could take away from this is the importance in updating all of your calculations when one of your measurements is changed. Although a key component of their design had been altered, the span of the bridge, they continued to carry on with the allowable stress and other calculations the same, which ultimately lead to its demise. However, if they would have factored this into their calculated values, then this disaster may never have occurred.
This disaster ultimately altered the engineering design process by highlighting a key step: readjusting all calculations every time the design is modified before proceeding to the next phase where it is actually constructed. Furthermore, this also represents the importance of a prototype before the actual design is built, since it allows you to determine if a design should work before beginning work on a full-scale model that will take lots of time and manual labor.
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