Case Study: The Quebec Bridge

The Quebec Bridge was constructed as a mode of transportation along the St. Lawrence River. During the winter, the river is covered with a thick ice blanket, which is the only time in which trade is able to travel across the river. Additionally, without the thick ice blanket, St. Lawrence River was a barrier between east and west of Canada. The desire to bridge the St. Lawrence River was motivated by Quebec’s need to be active in trade.
In 1887, the Quebec Bridge Company was formed. Therefore, the Phoenix Bridge Company was given the contract to design the bridge. The Head Engineer of the projected was Theodore Cooper, a respected engineer at the time. The Quebec Bridge was designed as a cantilever structure with two main supporters that were
The first being that both the top and the bottom chords for the anchor and cantilever arms of the bridge were mostly designed as straight pieces. This was done to make the construction of the bridge easier and cheaper. The top chords that attached to the anchor and the cantilever arms on the Quebec Bridge were created to be slightly curved, because the engineers believed it looked more aesthetically pleasing. However, the curvature of the chords added to the secondary stresses on the members, and reduced their buckling capacity. The engineering records for the building of the Quebec Bridge has stated in it, “As a rule secondary stresses are much more dangerous in tension that in compression members, which seem to have been the first to give way in the Quebec
Cooper’s stress calculations were made for the smaller length of the bridge. Cooper then recalculated the stress and discovered that there would be 7% more stress on the bridge. However, the Phoenix Company design staff and Cooper, recalculated the stress as team and discovered that there was 10% more stress. There were many financial problems with both the Phoenix Bridge Company and the Quebec Bridge Company, once they finally figured out the need to revise the assumed weights that were overlooked. The issue with the loads were discovered a year later, when a large portion of the bridge had already been built. Therefore, Cooper made the executive decision to accept the heavier loads and stresses to be within the acceptable limits. Cooper’s only alternative would have been to scratch the entire project and start over, and he did not want to stain his