69 Replies to “This Calls For A Team Of Experts”

  2. I’m guessing the truck driver needs to lose a few pounds…
    On the bright side, he probably shed 10 lbs. instantly when the bridge collapsed.

  3. Without knowing the bridge’s history, it’s hard to say what the cause might be.

    From what I saw and heard, the ping just before the collapse could have meant the failure of some brittle material. It could be a critical welding joint or rivet, or some feature which is known as a stress concentration.

    When ductile materials deform under load and they reach failure point, the break usually occurs suddenly. However, since the bridge was made from structural steel, and bridges are supposed to be inspected periodically, something like that would be hard to miss.

    Another possibility is fatigue failure. Components made from certain materials can withstand cyclical loading when that load is kept below a certain threshold. Exceeding that threshold stresses those materials and that stress is permanent. After a certain number of cycles, those components are likely to fail, often quite suddenly.

    The failure appeared to have occurred on the driver’s side of the bridge as the structure turned when it came down, maybe mid-span.

    Some forensic engineer’s going to be busy for a while.

    Any of my fellow engineers on SDA want to comment?

    1. I have two immediate questions:
      What was the load capacity of the bridge?
      How heavy was the truck?

        1. – And best of all, every truss bridge in Nova Scotia has a “Do Not Exceed…” sign right on it – or used to, last time I was there.

          Suppose the construction company knows what its equipment weighs? Especially when he has an excavator on the flatbed? “Ah, it’ll be fine…”

          And the guy in the safety vest was guiding the truck – that excavator barely fit between the trusses.

          1. – And yer average semi driver being no fool, I bet his train of thought all the way across (or at least, as far as he got) was “Oh, this ain’t gonna’ work… this CAN’T work… oh, shitshitshitshitshit SHITTTT…!”

            Wonder who gets fired?

      2. While those factors are, of course, important, they don’t explain the actual failure mechanism.

        Structures are designed with a safety factor. How much that SF is depends on the application and the corresponding design standards and codes, but, when I was an undergraduate, the rule of thumb was 50%. But there was also another aspect. If the design load is exceeded, the structure is considered to have failed, even though it may still be intact.

        For example, a structure can be designed to carry, say, 10,000 kg. With a 50% safety factor, actual physical failure can occur at 15,000. However, if the actual load was 10,500 kg, the structure is treated as if it has already failed as the design load was exceeded.

        If the load on the bridge was within the design limit, then the cause of failure must be something else.

        1. Not entirely true. The “safety factor” degrades over time depending on corrosion, etc.

          1. That’s probably true, but I did say “How much that SF is depends on the application and the corresponding design standards and codes” Degradation of structural material through natural causes is likely already accounted for.

      3. *
        robert nails this… but further, how does a commercial truck driver…

        1) not know the combined weight of rig & load

        2) not know the mandatory signed capacity of bridge

        ergo… underwriters at the insurance company just dodged a bullet.

        *

    2. The failure appeared to have occurred on the driver’s side of the bridge as the structure turned when it came down, maybe mid-span

      That’s what I saw … with one slight difference. It looked to me like the bridge support failed on the driver’s side. I didn’t see the collapse start at midspan (where one might expect), but it looks to me as though the support sheared off … or the bolts holding it sheared.

      Well … the Demolition contract just got discounted.

      1. The structure appears to buckle a bit past mid-span, but, the way the bridge was loaded when it failed, that might not be where the maximum deflection and corresponding bending moment occurred.

        This incident will keep undergrads in civil engineering busy for some time to come.

        1. I believe the buckling came an instant after the reaction failed, when the reaction failed the truss superstructure failed and buckled. But all I ever passed was structural engineering for Dummies. Hahahaha ha

          I can only imagine the rust built up on the bolts and steel plate holding the 4-corners of the bridge. Probably in quite an inaccessible location for maintenance. I saw the same deteriorated condition on a simple twin I-beam bridge accessing my client’s home recently

          1. But all I ever passed was structural engineering for Dummies.

            We covered forces in trusses in my freshman year statics course. I was introduced to bending moments and shears as a sophomore in the strength of materials course I took during the first term. Back then, just about all engineering students had to take those courses as part of a well-rounded technical education.

            The last two years were when we specialized in our respective disciplines. We had more fun and games in my senior year advanced SOM course when we got clobbered with things like slab stresses.

            I did rather poorly in those courses. Now that I’m much older and have had more education and experience, I can look at that course material, smack myself on the side of my head, and say “Of course! How simple!” It certainly wasn’t that way when I was in my late teens and early 20s.

            Corrosion, particularly in that setting, would likely have weakened critical joints. There would have been reaction products on the outer layers and those could have flaked off, reducing the cross-sectional area and creating small stress concentrations. Either way, it would have had a smaller load capacity.

            It wouldn’t surprise me if whatever failed had already been cracked and was close to breaking apart when the truck came along.

    3. BA.

      Remember the Tacoma Bridge disaster we all were shown in class..?
      This Bridge suffered from the same engineering failure (IMO) – ZERO box beam structure underneath the roadway….and yea, how old was this “temporary” looking bridge anyway.? Bolted Connections..~ 50 yrs.??

      Buddy shoulda crossed it doing 90….or more..!!

      1. The cause of the Tacoma Narrows Bridge was different.

        The wind blowing along the gorge on that day caused the structure to deflect. Specifically, it began twisting along its length. As I recall that was due to the shear forces generated by the wind over the surface.

        The wind kept blowing, which had the effect of adding energy to the system. That would increase the angular deflection, i. e., twist even more. (Think of what happens when one keeps pushing a child on a schoolyard swing. The range of motion increases as the pushing continues.) From what I was told as a young university student, the twisting was close to the resonant frequency of the structure. In oscillating systems, amplitudes increase rapidly near that point and, in the case of the bridge, they exceeded what the structure could withstand.

        The structure was deficient in that it failed under the wind conditions that day, though conditions like that were probably rare and difficult to foresee. The design itself would have been in compliance with existing standards and codes, as well as within the physical characteristics of the materials that were used.

        It could well be that the results of the forensic analysis of the NS bridge failure will result in the applicable standards and codes being revised.

    1. That truck driver’s gonna need clean pants.

      Thank God nobody was killed, is right. Sure looks like the truck & the excavator it was hauling was just too much for that old structure. Whatever structural engineer may have been involved in making that call is gonna have a bad day today.

      1. Something tells me no engineer was consulted before driving that load over the bridge. Probably didn’t occur to anyone to do that, they cross bridges all the time.

  5. The truck-tractor has 3 rear axles and the heavy haul trailer has 4, so one front steer plus 3 and 4 is 8 instead of the usual 5. About an extra 60,000 lb. \ 27,000 kg. That’s assuming they are loaded anywhere close to legal. The small picture shows a cab of an exavator or crane on a rather large set of tracks.

    It wasn’t the bridge’s fault or of the engineer who designed it. The load never should have been on the bridge. Was it the driver’s fault or Highways for permitting the load?

  6. Better call infrastructure Barbie…..I think we may have found a project

    2. Laundromat Barbie – she’s in charge of the money laundering. Liberals launder so well the dirt just disappears.

  7. They knew they were taking a risk. I wonder how much a bridge costs these days.

  8. No one read the article. The bridge was being replaced. This was just the accelerated demolition portion of the project. Gotta love the efficiency.

    1. Hmmm…
      Do you suppose the crane on the flatbed truck was being brought in to replace the bridge?

  9. Like the Germans crossing small wood bridges with heavy WW2 era tanks-a-lot.

  11. This was all explained in a Calvin and Hobbes strip years ago.
    Calvin asks his Dad how they know what weight limit to put on the sign for the bridge. His Dad explains that they drive heavier and heavier trucks over the bridge until it collapses, then they rebuild the bridge.
    For some reason, in the last panel Calvin’s Mom says, ” Dear, if you don’t know, just say so.”

  12. Salt. Water.
    That bridge was so rusted nobody could have calculated the safe load. That’s why it was being replaced.

    1. That was something that occurred to me as well. A few questions need to be asked in that regard, such as how badly corroded was the structure and was it noted during the last inspection?

      Here’s a famous example of a bridge failure in which corrosion was a major factor:

      https://corrosion-doctors.org/Bridges/Silver-Bridge.htm

      Based on that video, I’m wondering if the failure was caused by a critical component on that bridge which might have been sufficiently weakened by corrosion and weathering.

      1. I worked in the pipeline industry for years. We had some of the best Metallurgical Engineers on the planet working on corrosion protection for pipelines (by the way, one of the worst things for pipelines is wind turbines being constructed nearby because with the underground cables they induce a current that is strong enough to induce corrosion). One of these engineers in Calgary went down to see the construction of the “Peace Bridge”…..and when she came back, she said “that bridge will keep the Engineering Faculty at U of C busy for the rest of their lives”.

        2. On the other hand, an example of robust and sturdy design is the High Level Bridge that crosses the North Saskatchewan River here in Edmonton. It’s been there for more than 100 years. Then again, one could probably remove about a third of the structural members and it’ll still stay in place.

  14. that was out right STUPIDITY on the part of the the truck driver , and the guy guiding him. As the weight of the rig was more than the new structure was designed for. Only cause was stupidity, nothing more!!

    1. Also, if they had spent time planning the move, whomever approved the route over that bridge should be part of that discussion.

  15. That’s the crawler and house for a conventional crane, the ones with the lattice booms.

  17. I was thinking of this when I woke this a.m.
    Yes, good old salt water corrosion, a couple of you beat me to the suggestion. When one lives in the Maritimes, as I did for almost 20 years, it’s a smell you never forget. On a rainy day, especially, one can typically smell the fish-scent in the air.

    1. The oil company I worked for right after I got my B. Sc. had a set of design standards which included pipelines. Apparently, the firm was concerned about locating them within 250 km of a coastline, so any line inside that limit had to have things like cathodic protection.

      On the other hand, that same outfit, while claiming it was exacting and precise in its design codes thought nothing of buying or renting a piece of machinery, doing next to no maintenance on it, running it flat out until it fell apart, and then suing the vendor, or even the manufacturer, claiming that it received a piece of junk.

        1. It’s been said that aircraft design standards are often written in blood, as, I suppose, are those for buildings and bridges.

          Those standards take into account the best knowledge and experience, but, sometimes, there are situations, or even failures, which those standards don’t cover. Those could be situations that nobody ever thought would occur or one couldn’t foresee or test for. (One example of that were the crashes of the de Havilland Comet. There’s a reason why passenger windows have rounded corners.)

          Then, of course, there are things like acts of malice which lead to failures. Leslie Robertson’s design for the World Trade Centre allowed for planes crashing into the towers accidentally but not deliberately. Half a century ago, nobody would have thought that someone would do something like flying a plane into the side of a building on purpose.

          1. Just remember B A, there is no cure for stupid. this applies to so many things it gets tiresome.

  18. Why didn’t they unload the tractor, drive the truck across and then drive the tractor across? Wouldn’t it be obvious that a flimsy bridge about to be replaced might collapse under such a load? Maybe that’s one of those new truck drivers trained virtually.

    1. Ya know, Justin … for all dat fancy book learning and whatnot … sometimes simple common sense (like drive the equipment across on its own – to lighten the load) is far more important than engineering calculations. Brilliant!

      OTOH … I suspect the Heavy Equipment Operators UNION only allows their operators to drive the equipment once delivered to the site. The Heavy Equipment Transport UNION is responsible for all equipment moving.

    2. We have mining shovels that are moved from one pit to another like that.
      When they get to the bridge they are unloaded and walked across.

      And speaking of cool machines for moving mining shovels and excavators:

      https://www.sleipner.fi

      They work quite well once you get the hang of it.

      A slightly more conventional truck and trailer method.
      They can ditch the trailer and hook onto a mining truck and move them as well:
      https://towhaul.com/en

  19. All I got to say: Did the load get weighed before heading for the bridge? Can the driver read? Who cares if the P. Eng. said OK, if he/she/it was even involved.

    1. Where was the driver born and raised? Never used to have to ask that question, but today, hey who knows?

    2. There is a guy in our gun club that is an inspector for that sort of thing, truck weight. He has some good horror stories.

  20. The truck may very well have met the weight load restrictions (although I have my doubts) but could’ve been the proverbial straw that broke the camel’s back.
    Bridges undergo tremendous amounts of stress over their lifetime and sometimes will energetically disassemble to let you know it’s had enough.

    Then there’s this – https://www.youtube.com/watch?v=c-4SaX9TZ4I

    1. Don’t buses that size weigh about 13 Tons? Empty? Couldn’t find a reference for them, just dredging my memory.

    2. That’s a good example of some of the concepts I used to teach in my strength of materials course.

  21. I’m thinking the collapse was due to cheap (ie. crappy), Chinese steel and an engineering firm from Quebec.

    1. The source and quality of the structural steel as well as who designed the bridge will be taken into consideration during the investigation.

      1. And I’d be willing to bet the bridge was at least 70 years old, riveted together, and the steel made in Sydney. Those days are long gone…

        And you’re half-right, B A – all that will be carefully taken into account. Unless the move was pre-approved by the Nova Scotia government – in which case nothing more will be heard of it. Sorta’ like the RCMP never, ever, telling anybody what guns the Nova Scotia shooter used…

  22. If the bridge was already in trouble what kind of thought process would conclude it was safe to drive a heavy truck and equipment over it? Not a lesson in how to dismantle an old iron bridge 101.

  23. Why did the crane have to be on the island side of the bridge and not the mainland side?

  24. Couple of months ago there was a fully loaded grain truck – at least forty tons gross – tried crossing a bridge in North Dakota rated for ten tons. Needless to say the bridge collapsed and the registry of historic bridges got a tad shorter. We drivers aren’t the sharpest pens in the drawer, that’s why we drive.

    1. Scooter, most professional drivers that I knew were some of the sharpest pencils in the box. I still know a few that are far more intelligent than most of the so called intellectual elite in this country. One imported driver caused a great deal of pain out west, you know that to which I refer. Diversity is not always a good thing.

  25. This bridge is on a NS government five year plan list of “priority replacement projects” for 2015-16. It appears every year since. But contract only let in 2020. This bridge is quite old and was clearly at end-of-life. Someone didn’t do their due diligence on the condition/capacity of the bridge before trying to move that gear.

    http://www.nsrba.ca/files/Nova%20Scotia%205%20year%20plan.pdf

    1. Alternately, that bridge might have been a mishap waiting to happen.

  26. Remember the I 35W bridge over the Mississippi in Minnesota that went down in 2007. It was only 40yo.

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