Hi and welcome to Failurology; a podcast about engineering failures. I’m your host, Nicole, and I’m from Calgary, Alberta.
We made it to the holiday season!!
The last month or two have been very busy for me, and while I’m thankful to be working and healthy, boy do I ever need a nap. There’s always this big push at work from contractors and developers to get occupancy certificates before everything shuts down for the holidays. So my December is usually stressful. But then I get a bit of much needed time off, which I am very much looking forward to after this crazy year. I can’t believe it’s only been 9 months since COVID changed our lives in Canada; this year has been the longest decade ever. But vaccines are arriving and have started being distributed to health care workers. And while I can start to see a light at the end of the tunnel, it’s not going to be easy to get there. We still have a lot of new and active cases in Alberta that need to get under control and we are in lockdown until mid January at the earliest. Which I am fortunate enough to be ok with; whatever we have to do to keep people safe and healthy is fine with me.
So whether you celebrate Christmas, Hanukkah, Kwanzaa, or none of the above, I hope you are happy and healthy this holiday season. And if you don’t get to be with your loved ones in person this year, I’m sorry. If you’re feeling lonely or bored this holiday season, reach out to me. We can nerd out on engineering things, or chat about whatever else catches your fancy. I would love to hear from you. My twitter handle is @failurology. Or if you want to email me, you can send it to firstname.lastname@example.org. I will put links to both in the show notes of this episode.
Today’s episode is a very iconic Canadian failure; the Quebec Bridge Collapse. This is the first Canadian failure I’ve covered. Not only did the bridge collapse twice, the failure also jump-started the creation of engineering regulations and ethics commissions and led to the iron ring tradition of Canadian engineers.
I’m going to dive into all of that soon, but first, the news.
This week in engineering news, a 3 storey apartment building in Germany was made with the help of a 3D printer.
The apartment building is 3 floors and about 375 square metres, containing 5 apartments.
The German formwork and scaffolding company, Peri, is using a BOD2 printer, which they claim to be the fastest available 3d construction printer. This printer can print a 1 square meter façade in 5 minutes! It can also move throughout its frame, to any part of the project, without needing to be re-calibrated.
The project consists of printed concrete for all of the walls. A good portion of the interior walls are curves and the 3d printer traces the wall outline over and over adding a layer each time. There is a gap in the walls as well, which I assume will be filled with insulation for thermal or acoustic reasons. The floor and things like pipes, ductwork and electricity can’t be printed in and so they will be installed in the traditional fashion.
The printing project is expected to finish in March or April of 2021.
I knew this day would come eventually, and it’s pretty exciting and just the tip of the iceberg. Other teams have built houses and single storey structures, but this is the first multi storey apartment building that I’ve been able to find. There are several videos online about the project, I recommend checking them out. Watching the printer is oddly satisfying, kinda like power washing videos.
If you want to read more on this 3d printed apartment project, check out the link in the show notes.
Today’s engineering failure is the Quebec Bridge or Pont De Quebec collapse; the bridge that collapsed twice. The Quebec Bridge collapse is said to be Canada’s worst engineering disaster.
Before I get into it, I want to take a second to mention that while I am Canadian, my French is not very good. Je parle un petite peu francais. I hope I get most of the French pronunciation right. Wish me luck.
The Quebec Bridge connects Quebec City and Levis (Lee-vaiz) across the St Lawrence River.
At the narrowest section, the St Lawrence River is 3.2km wide, 59m deep in the middle, with an average water velocity of 13-14kph and a tide range of 5m. In the winter, ice used to get stuck in the narrows and pile up to 15m high.
Before the bridge, boats were used to cross in the summer, and in the winter they used an Ice Bridge to cross. There was no crossing in the spring or fall when the ice was too thick to cross by boat but too thin to cross by ice road.
Montreal built the Victoria Bridge in 1859. Quebec City wanted to remain competitive in trade and needed a year round crossing.
Quebec City residents had been asking for the bridge since as early as 1852. A site was chosen where the river narrows roughly 10km upstream from downtown Quebec City, but then nothing really happened for several years.
But in 1898 a design competition was held, and the Phoenix Bridge Company’s design was selected.
Their design was for a cantilever bridge with 488m between supporting piers. A cantilever bridge is a bridge with two piers on either side of the river crossing, and then the bridge deck spans across between those two piers. They call it a cantilever bridge because the bridge decks are cantilevered or supported out from the support piers, with no pier in the middle of the span. These types of bridges are common when there is significant river traffic flowing under the bridge; any piers in the middle would restrict access and limit ship sizes that could pass through.
Shortly after 530pm Aug 29 1907, during construction
The southern cantilever span, which at the time spanned 180m over the river, twisted and fell 46m into the river.
75 workers, including many of the Kahnawake (ka-na-wa-ke) tribe, were killed – reportedly 86 were on the span at the end of the work day – 11 survivors
Among those who perished were Benjamin A Yenser, General foreman of erection for the remainder of the project, worked for Phoenix Bridge Company – Arthur Birks, Resident Engineer of Erection
The crash was heard in Quebec , locals thought it was an earthquake
Causes – The cause was ultimately determined to be faulty design and inadequate engineering supervision
Initial Construction and First Collapse
There were four parties involved in the initial construction of the bridge. These are the major players.
Government of Canada – funded the bridge
The Quebec Bridge and Railway Company – responsibility for completing the structure
Chief engineer – Edward Hoare (whore)
Consulting engineer – Theodore Cooper of New York
inspector of erection - Norman McLure
Phoenix Bridge Company – Phoenixville Pennsylvania – design and construct the superstructure
Phoenix Iron Company – fabricate steel components
I’m going to reference these people while explaining the first collapse, but don’t worry, I will remind you who they are as I go.
Cooper was a consulting engineer out of New York hired to design the bridge concept put forth by the Phoenix Bridge Company. Cooper had designed the Second Avenue Bridge in NYC, which was an elevated train bridge from 1878 to 1942. After investigating the riverbed of the St Lawrence, Cooper recommended the piers be closer to shore, increasing the span from 488m to 549m. – This is where things started to go wrong.
The bridge design included anchor arms on each end, support piers in the water, now 549m apart, cantilever spans from each pier. On the cantilevered spans, the bottom structural members were in compression, and the top members were in tension, with members in a lattice pattern in between.
Let’s try an experiment, shall we. If you’re driving, just imagine it. Hold your arm out to your side, you are the support pier and your arm is the bridge deck; now imagine a downward force is being applied to your hand. As your hand moves down, the top of your arm is elongating (or in tension) and the bottom is shortening (or in compression).
The Quebec Bridge is the longest cantilever span in the world still to this day
And the bridge deck sits 46m above the river at high tide
Noticed during construction
Construction for the Quebec Bridge began Oct 2, 1900.
There were several problems noticed during construction, but their importance was discovered too late.
First, pre-drilled holes for sections that were supposed to bolt together, did not line up. This implies additional stresses on members that would put them out of alignment; meaning they weren’t where they were supposed to be. Today, you can survey members to make sure they are in the right spot, but this was 1907.
Some ends of pieces of steel that had been joined together were bent, specifically on the lower chords of the south arm. Remember the arm exercise, these members were in compression.
The bending was first noticed on June 15th and observed until collapse on August 29th. Deans, the Chief Engineer for the Phoenix Bridge Company, insisted work continue. Remember he was more focused on the business or the project, not the engineering.
Deflection of the south arm lower cord members ranged from 1.5 to 57mm across approx. 15 members. 1.5mm may have been within tolerance or determined to be a pre-existing condition and did not cause immediate alarm, but 57mm certainly raised a red flag. The manufacturer guaranteed the members were straight when they left the yard.
However, one member was dropped and bent while at a storage yard. All of the major structural members were tagged; the dropped one in particular was tagged A9L (which was a chord in anchor arm (A), ninth panel (9), left or west side of the bridge(L) ). It was believed to have been repaired. But later determined to be the triggering cause of the collapse. – A9L went from 19mm to 57mm deflection in 2 weeks. A9R, which is the same chord on the right or east side of the bridge, was bent in the same direction.
Based on what we know now, the bridge was likely to collapse regardless of whether A9L was damaged. But as tragic as the collapse was, it was likely less destructive than if it had happened after the bridge was opened to the public. Why can’t these things happen in the middle of the night, when no one is there.
Several weeks before the collapse, Cooper, the consulting engineer who designed the bridge, was notified by McLure, the director of inspection for the Quebec Bridge and Railway Company, by letter, of the bending issues on site and suggested corrective procedures. The members with the highest compression load were starting to buckle
Cooper rejected the proposal, asking how the bends occurred – he believed that the chords were damaged during erection
When someone says there is a problem, you check your numbers, even if you disagree with them, you double check. A lot of engineers work in excel or other software, which makes it easier to re-run formulas under different parameters with minimal time spent.
Letters went back and forth for 3 weeks between Cooper the consulting engineer, McLure the director of inspection for the Quebec Bridge & Railway Company, and Deans, the chief engineer for the Phoenix Bridge Company acting as a business manager.
Cooper sought to understand how the steel was bent and rejected multiple explanations
Szlapka, the design engineer for Phoenix Bridge Company stated he was certain the bend was put in the chord ribs at the shop, but he later admitted that he never actually saw the chords in question at the shop.
A couple of days before the collapse, on August 27th McLure, director of inspection for the Quebec Bridge and Railway Company found additional bending of other chords in the truss work and measured the deflection
Erection of steel was suspended until Cooper, the consulting engineer, and the bridge company could evaluate the situation
McLure, the director of inspection, went to New York to discuss with Cooper – but unbeknownst to McLure, Hoare the chief engineer for the Quebec Bridge and Railway company, authorized the work on the bridge to resume.
Upon discussing with McLure, Cooper wired Phoenixville, where the Phoenix Bridge Company was located the the message “add no more load to the bridge till after due consideration of facts”
McLure, thinking work was still suspended, not realizing Hoare has resumed it, didn’t urge direct contact with Quebec
Due to a telegraph strike it’s unclear if Cooper’ telegram to Phoenixville was undelivered or unread. One article noted Deans, chief engineering for the Phoenix Bridge Company, read the wire and ignored it
Within hours the Royal Commission was established, consisting of three investigators, Henry Holgate, John George Gale Kerry, and John Galbraith. Their investigation came to the following conclusions. There are a lot of them. I will let you know when I’ve listed them all.
Failure occurred from lower chords A9L and A9R in the anchor arm of the main pier – due to defective design. Remember that A9L was damaged in the steel yard and believed to be repaired. But the commissioning believed the members were undersized and failure would have occurred regardless.
Cooper increased the allowable stresses on the compressive (lower) members. He had developed a formula to calculate allowable compressive stress which was 3.3-8.7% higher than stresses in use today. The design was unsafe practice and questioned for being unusually high but based on Cooper’s reputation the questioning didn’t go very far.
The design loads were underestimated.
Stresses calculated by Szlapka, the Phoenix Bridge Company design engineer, using Cooper’s, the consulting design engineer, estimate of total dead weight was from the start of the design process. But the dead weight changed during design, for example when the span changed from 488m to 549m, and stresses were not recalculated.
Assumptions have to be made to start the design; you can’t start to build the bridge without at least a guess of how heavy it will be. But once you have a design, you have to recalculate those loads
Cooper was made aware of the underestimation of weight, but only after considerable material was fabricated and construction had begun. Cooper calculated an underestimate of 7-10% which he believed was still within acceptable tolerance. Later analysis showed the underestimate to be about 20%. There was minimal budget for testing, and once said budget was available Cooper said it was too late
The top and bottom chords were designed as curved members, which resulted in difficult fabrication and reducing buckling capacity. It also resulted in increased secondary stressed on members, which are more dangerous in tension than compression
On top of the design issues, the commission also found personnel problems.
The Quebec Bridge and Railway Board took 2 years and half a million dollars to prepare specifications, but expected engineering companies to prepare detailed competitive bids for free in 4 months
Cooper, the consulting engineer who designed the bridge, assumed a great responsibility for inadequate salary and there were no provisions in that salary for him to hire staff to assist him. The pay was so small he wasn’t able to outsource any work to junior staff leaving him little time to investigate the data and theories used in the design and allowed errors to go unnoticed. His reputation gave false security that no issues would arise and therefore he was scrutinized less. He even rejected an independent engineer checking his work. The unwavering trust in Cooper is interesting because he was unable to visit the site in the two final recent years of construction due to poor health. Distance from the site and minimal tools also made communication difficult. This wouldn’t be permitted today; engineers are legally required to review their designs during construction. If they cannot review in person, they have to appoint someone to do so on their behalf. This is what I do, except for plumbing and HVAC systems.
No clear order of command existed. It was assumed that authority rested with Cooper, even though there was no one on site qualified to oversee construction
During construction engineers wasted time arguing over the cause of the deformation and whose fault it was that the bridge collapsed – some workers refused to show up because of the deformation – engineers must be open minded to ideas and hands-on experience of laborers and contractors. Not only are they down there in the trenches, spending hours a day looking at small details of the bridge construction, they’ve probably done enough of these to know when something looks off.
Cooper wasn’t the only one criticized, the investigation found that appointing Hoare as chief engineer for the Quebec Bridge and Railway company was a mistake, as he was not believed to be technically competent to control the work
Deans, the chief engineer for the Phoenix Bridge Company was believed to be lacking in caution, and failed to appreciate emergencies that arose
Szlapka, the design engineer for Phoenix Bridge company, criticized Cooper for making the bottom chords curved for artistic reasons and for not visiting the Phoenixville plant during fabrication.
The Royal Commissions investigation found that loss of life could have been prevented with better judgement and that the failure was caused by design flaws, not manufacturing.
After the investigation, and a 2 year removal of the collapsed portion, the Government of Canada, realizing the bridge was a vital transportation route, decided to rebuild.
A 3 person board of engineers was established to prepare plans and specifications and supervise the work – This time, the board’s duties and power were clearly defined. There were also some significant design changes.
The original bridge was intended to be constructed in place, cantilevering out the bridge decks from each side until they met in the middle. But the re-designed construction spanned the bridge decks partway, with the middle span built on shore and floated out to be raised into position.
The cross-sectional area of original compression members was half a square metre vs 1.25 square metres with the new bridge. And the new bridge weighed 2.5x as much as the initial design; which the design properly calculated and accounted for. The new design also revised the bridge to wider piers and straight lower chords
The St Lawrence Bridge Company of Montreal was hired to erect bridge
But on Sept 11, 1916, at 11am - while lifting the centre span into place, little more than 7m above the water, a sharp crack was heard and the span slid off its four corner supports into the river next to wreckage from original collapse.
13 workers were killed, 14 more were injured
This was just a few days past the 9 year anniversary of the first collapse and this section is still there today.
An investigation found no design flaw. There was a material failure in one of the four bearing castings that temporarily supported the span while it was transported and hoisted
The St Lawrence Bridge Company took responsibility, a second span was constructed and design of the support bearings was revised.
The new span was lifted into place over three days in August 1917
The bridge was completed in 1917, and opened to traffic in 1918. The Official opening was Dec 3, 1919 (ironically Cooper died 2 days later). The final cost was 22 million dollars, which is over 330 million today
Here’s a fun fact, that really has nothing to do with the collapse, but I thought it was interesting. The bridge was officially opened by the prince of Wales, Edward viii who is Queen Elizabeth’s uncle. Edward the 8th abdicated the throne to marry an American divorcee, allowing his brother Albert, Queen Elizabeth’s dad, to ascend to the throne.
Over the years, the bridge has offered passage to road, rail and pedestrian traffic.
Rail –the bridge had two rail lanes until 1949, then reduced to one and even carried streetcar line at one time
Road – the first road lane opened in 1929, second lane in 1949 and third lane in 1993
Pedestrian – one walkway now, originally two
The bridge has been owned by the Canadian National Railway since 1993
Lessons learned – Gordon C Andrews
Provide adequate funds for large-scale projects
Hire capable and competent professionals
Define clearly the duties, authority and responsibility of personnel
Discuss design decisions and technical problems openly
Monitor the work on site adequately
Ensure that communication is rapid and accurate
Provide adequate support staff and pay for professional people
Following this collapse came the forming of: American Institute for Steel Construction (1921) and the American Association of State Highway and Transportation Officials (1914) –both as means to fund research which was too difficult and expensive for manufacturers to do themselves.
As I mentioned at the top of the episode, the collapse jump-started the creation of engineering regulations and ethics commissions and it also led to the iron ring tradition to symbolize humility and fallibility of engineers.
Today Engineers Canada defines the five duties of an engineer;
A duty to public safety – to put public safety and health above all else
A duty to the client – do not disclose project specific information to the public unless there is a safety risk, and present consequences if professional decisions are overruled
A duty to the employer – no moonlighting or accepting money to shortcut designs
A duty to the profession – self governance and reporting unprofessional conduct
A duty to self – adequate compensation and continuing professional development
Check out the podcast page, link in show notes, for photos from this week’s episode. And if you want to chat with me, my twitter handle is @failurology or you can email me at email@example.com. Thanks everyone for listening. If you’re enjoying what you’re hearing; please rate, review and subscribe to the podcast so more people can find it. And don’t forget to tune in next week to hear about the Hartford Arena roof collapse; the first computer aided design failure. But more on that next week. Bye everyone, talk soon.