The Quebec Bridge Failures

• Design considerations• History: What happened?• The day of the collapse• Factors contributing to the failure• Conclusion• The Iron Ring – a consequence of the

collapse

Design Considerations

• The bridge was necessary in order to connect Quebec City to the main transportation link between Maine and the province of Quebec

• The 2800 foot bridge was required to Have an 1800 foot single span Have 150 feet of clearance Be 67 feet wide to accommodate 2 railway lines,

2 street car tracks and 2 roadways• Steel plate cylinders were to be used as the

main compression members

What happened?

• 1882: The Quebec Bridge Company (QBC) was awarded the contract

• 1897: Theodore Cooper was contracted to overlook the ambitious project

• 1899: QBC officials met Cooper to discuss bids for the project. The Phoenix Bridge company (PBC) won the project.

What happened? Contd.

• 1900, May 1: Cooper lengthened the span of the cantilevered bridge from 1600 to 1800 feet

• Cooper also recommended some modified specifications that would allow for higher unit stresses caused by the longer span

• 1900 – 1903: The project remained stagnant until the Canadian government issued a $6.7 million bond to pay for the work

What happened? Contd.

• Despite no revision of the original calculations, construction commenced almost immediately

• Cooper visited the site only 4 times between 1900 and 1903.After May 1903, he never visited the site again, citing poor health requiring him to remain in New York

What happened? Contd.

• Robert Douglas criticised the high unit stresses in the new design

• Belief in Cooper was such that these criticisms were ignored entirely

• 1905: Norman McLure, a recently graduated engineer, was placed in charge of the project on site, as Coopers right hand man

What happened? Contd.

• 1907: McLure wired Cooper regarding bending of the lower chords, 7-L and 8-L

• 1907,August 7: McLure reported to Cooper that some buckling was occurring in chords 8-L and 9-L

• Confusion was created by Chief Engineer Deans, who declared the chords were bent when leaving the workshop

What happened? Contd.

• 1907, August 27: An increase of deflection of a further 1.5 inches was measured

• A letter was sent to Cooper outlining the increase of deflections in just 7 days

• Work was halted due to safety fears

August 29th: The Collapse

• McLure was dispatched to New York to consult with Cooper

• McLure reached Cooper at the same time as the letter which had been dispatched 2 days previously

• Cooper believed the bridge would stand long enough for a study of the deflections if it was not put under any further loading

August 29th: The Collapse contd.

• A wire was written by Cooper, instructing Chief Engineer Deans to ensure no further loading was placed on the bridge

• Unbeknownst to Cooper and McLure, construction had recommenced that morning

August 29th: The Collapse contd.

• In his rush to meet his train, McLure did not send the wire to the site

• A meeting was set up for that evening to discuss the deflections

• Almost exactly as the meeting broke up,at 5:30pm, the bridge collapsed

August 29th: The Collapse contd.

• 85 workers were on the bridge when it collapsed

• Only 11 survived

Factors contributing to the collapse

• Cooper turned the management of the work crews to Peter Szlapka, but Szlapka had no experience of supervising construction

• McLure was the only team member in contact with the workers

• Though McLure noticed the problems with the bridge, he was too young and inexperienced to be able to take action to correct these problems without permission from his superiors

Factors contributing to the collapse

• The 200 foot increase in span length was almost entirely ignored in design considerations

• The estimations of self weight were out by 8million pounds (~3630 tonnes)

• Inadequate riveting of some members due to deformations left some key elements unstable

Factors contributing to the collapse

• No actions were taken when deformations exceeded expectations

• Delays in communications between the site and Cooper led to action being taken too late

• The decision to continue working led to overloading of the unstable structure

Conclusion

• Human error led to the collapse of the bridge

• Royal Commission of Inquiry report of the collapse:

"We are satisfied that no one connected with the work was expecting immediate disaster, and we believe that in the case of Mr. Cooper his opinion was justified. He understood that erection was not proceeding; and without additional load the bridge might have held out for days."

Conclusion contd.

Chief Engineer Deans was rebuked for his poor judgement in returning to work without proper analysis of the situation

The Quebec Bridge Company was criticised for appointing unqualified supervisors

Conclusion contd.

• “…the failure cannot be attributed directly to any cause other than errors in judgment on the part of these two engineers [Theodore Cooper and Peter Szlapka] ...A grave error was made in assuming the dead load for the calculations at too low a value...This error was of sufficient magnitude to have required the condemnation of the bridge, even if the details of the lower chords had been of sufficient strength."

The Iron Ring

The “Iron Ring” tradition of the Engineering Institute of Canada arose from this disaster. The ring is worn as a reminder of the possible consequences of an engineer’s actions. It serves as a visible reminder of the lessons to be learned from the fateful bridge.