What the fuck is going on in Montreal?
First an overpass collapses (in Laval). Then they shut down multiple lanes of the Ville Marie because of cracks in support pillars, but insist the rest of the structure is perfectly safe. The more bridges and overpasses they inspect, the more they close for emergency repairs.
Now we’ve got an underground mall closed in the downtown core because a massive slab underneath a road dropped 2 cm yesterday. They shut down a dozen blocks to pedestrians, let alone cars, and shut down a super-busy stretch of the green line metro.
This is ridiculous. Absolutely fucking pathetic.
And it seems like one thing is to blame.
All of this craptastic construction was done in the 60s. What the fuck were people doing, putting weed in with the concrete? Dropping acid and then trying to lay steel bars in a straight line?
Unbeknownest to most people, including voters who refuse year after year to support bond measures or increase revenue funds for infrastructure maintenance and improvements, large structures like overpasses, highways, and bridges (especially bridges) aren’t just built and last forever without a thought; they require regular inspection and maintenance; as they age, the strength and resistance of concrete changes, joints fatigue and corrode, and the cummulative damage of ever increasing amounts of traffic take their toll. These things just don’t last forever, or even for more than a couple of decades without repair. When you neglect to fund the repairs, you end up with stuff that breaks.
I’m between amused and exasperated with the mass of people expressing their shock and surprise that the failure of the 10W bridge in Minnesota and that it could happen “even in 2007!!!” If you owned a house and never sprayed for termites, patched or replaced the roofing, and shored up the foundation where it starts sinking for fifty years, you’d have a house that is falling apart. Why do people expect a bridge–one that sees the weight of an increasing volvme of commercial heavy haulers–to last forever without maintenance?
Much of the infrastructure was built in spurts during economic booms (ie right after WWII) so it’s very likely that you could see several failures in a concentrated area. Also, there may be some knee-jerk reactions to up the rate of inspections since the Minnesota fiasco.
Sorry, after 40 years, I’m not buying the ‘craptastic’ construction arguement.
I’d look to other factors than original construction, myself: salt is wonderfully evil stuff for most of the things we use for construction materials. It corrodes metals, and salt water weakens and erodes concrete. I’m not sure, but I believe that if the water gets to the right concentration of salts it will actually dissolve concrete, as well as eroding it.
But, whatever long-term problems salt on the road ways brings, it doesn’t change that it saves lives during winter by reducing or eliminating ice formation.
No quick answer, just more support for Stranger’s point: inspections and maintenance are really important.
<“sea story” hijack>
While I was working as a boiler water chemical treatment company I saw one of the most annoying consequences of what I’d call “minimum necessary” budgeting.
Treating boiler water is a very good idea - it can extend your boiler’s service life by 100%, or more, depending on how closely you monitor the chemicals, and keep them within the ideal postion on the Whirl-Purcell* curve. They also help prevent scale formation, making for a more efficient boiler, too.
But, schools and towns often get maintenance emergencies. And something has to come out of the budget to pay for the emergency fix needed for the roof, or the pool, or some other important piece of capital equipment. Very often, when that happens, the maintenance people are asked, “Okay, we’re screwed. We need to make up X dollars from the budget right the fuck now. What can we cut with minimal effects?”
Very often the maintenance people would suggest that boiler water treatment was one of those things that they could do without for the rest of the year, saving some money for the emergency. After all, while there would be some scale formation, just skipping one year of treatment in a low-pressure boiler wouldn’t do irreperable harm. And the maintenance people would make it clear that they’re suggesting this as a one time thing for the budget emergency. And the bean counters would say, “Yup. Just this one year.”
And inevitably, come budget time, the next year, the bean counters would say, “Hey, I see that we had no adverse effects from discontinuing boiler water treatment last year, so we don’t need it this year, either.” The maintenance people would wave their hands and get excited, and the bean counters would ask, “Will the sky fall if we skip this year, too?” And after some hemming and hawwing, the maintenance people would admit that, no, in all likelihood, the sky wouldn’t fall, this year, but it would be reducing the service life of the boiler.
Repeat about five years… then come November when the boilers are lit off for the test firing after being laid up all summer, after seven years without boiler water treatment, and there’s a leak in the fireplate, or the tubes crack under pressure… and now the latest budget emergency is that they need to replace a boiler in an emergency situation - with all the penalties for costs that such a rush job entails.
And invariably we got called back in, after the boiler manufacturers point out that the warranty was good only so long as the school district maintained a proper chemical treatment program. And we’re told that it will never, ever, ever happen again.
Then three years down the road, a new bean counter comes in, and the roof, which had had its own routine maintenance postponed to pay for the emergency boiler replacement is now leaking like a sieve - so they rob Peter to pay Paul again, and discontinue the boiler water treatments once more.
ETA: I may have the name of the Whirl-Purcell curve butchered. If so, my apologies. It shows corrosion rates as a function of pH, and Phosphate concentrations in boiler water.
True, but your point can remain valid and still allow for shoddy initial construction.
We have rail bridges here built in the 1870s for diminutive 200 ton steam trains that are now taking 6000 ton coal trains (often two passing one another). If a freeway carrying 1 to 20 ton vehicles can’t last forty years (even with shoddy maintenance), there is something wrong.
Things in the past (and the 60’s are important here so wait a minute) were often heavily overbuilt. I mean heavily. When TheLoadedDog says
there’s no joke. In the 1870’s, people overbuilt their stuff. They made it tougher and more reliable. It wasn’t as functional or complicated, but it was reliable as all get out. Certainly noteverything survived, but more often than we might have thought. (And this, by-by-by is soething which burns me about modern stuff. It’s just plain hard to find good-quality items which last, even if you are willing to pay more.) Before, say 1950 or so, engineers hadn’t really known exactly what forces things could take. So they just plain guessed. Thy knew from experience, rules of thumb, and some testing what metal could take, for instance. They took the high range and then, say, doubled it. And built for that capacity. It was more expensive but very, very safe.
Fast forward. By the 60’s, people were a lot more confidant of their ability to make structures,and I wouldn’t doubt that given the 60’s zeitgeist, they wanted to push the limits and be “daring” as well. At the time, people didn’t always leave nearly enough excess capacity - extra supports, or concrete, or whatever. After all, they knew what limtis they were designing for, why go beyond that? By the 70’s, they’d started realizing that they really, Really, REALLY neeeded more capacity in their designs. But people didn’t go out and tear down stuff fromthe 60’s.
Now, speaking as to the tax situation. I’m pretty darn sure that money is and has alays been there. The problem is that no one wants to budget properly. Why spend money on boiler maintenance when you can get new office furniture? Why spend money on bvruidge repair when you can earmark it for pedestrian walkways and bike trials? (Which will give you PR opportunities and have a shiny plaque with your name on it.) And yes, that’s exactly what happened in the Twin Cities Bridge disaster.
I’m building off your comment, smiling bandit, but this is more directed towards TheLoadedDog’s post.
But an inevitable consequence of that is that in the 1870’s they were spending far more than they needed to on construction. And probably with the commensurate increase in lives lost during construction.
If you ask most engineers if the 1870’s bridges were well designed for the job they were supposed to, I believe most will say, “No!” The fact that they’re apparantly taking 30 times their original design load without any concerns about overstressing the structure is an indication that the original builder took on a huge expense that shouldn’t have been there, in the first place.
AIUI, the majority of modern structures are designed with a 100-200% safety factor. That is, the structure should be able to withstand two or three times the normal, expected maximum stress. Which is usually figured along the lines, for a bridge, of having max traffic, of current road limited legal traffic, during an additional stress, like a 100 year storm, or such. If the engineers are trying to be particularly forward looking, they’ll suggest a 400-500% fudge factor, to allow them to expect that their structure will be able to withstand the stresses from increased loads as traffic goes up. But that’s pretty rare, AIUI.
But expecting a 4500% safety margin (the minimum I’d expect if they’re letting 30 times heavier loads go over the bridges mentioned - it’s only a 50% margin for the load that has been claimed for the bridge in question.) from a structure is incredibly expensive and, likely, insanely over building. Just for one example, while population in general, in the US, is going up, there are a number of metropolitan areas that are leaking people. Here in Rochester, Kodak and Xerox are both moving a lot of their operations out of the city, with a predictable result for population numbers. Unless, and until, things change for the demographics here, it’s asinine to talk about building for a 4500% safety margin.
And I agree with this. Heck, I’ve sat in little pubs built in the 1860s with beams holding up one floor that are so massive they could hold up thirty. Sure, those old things were over-engineered. But I’d wager that a freeway that collapses under normal use after a mere forty years was under-engineered. I’d also suggest that any civil engineer worth his salt would ask himself, “Am I building a structure for a strapped-for-cash municipal authority that will, frankly, probably skimp on periodic inspections and maintenance, or am I building a private bordello for Donald Trump?” and if the former, then build something that can be mildly neglected and still hold up for, say, a century. A 1000% safety margin might be a big ask, but a more reasonable one… well, why not?
The problem with the I30W bridge collapse, for talking about what safety margins should be incorporated, is that so far I’ve yet to notice any figures that show how the current load on those roads compare to the load that the roads were designed for. (That information may well be out there, I just haven’t looked, myself.) AIUI Minneapolis has experienced a huge increase in population in the past two decades. It wouldn’t surprise me to hear that the original design allowed for a 500% safety margin, while the actual use at the time of the collapse had only a 50-100% safety margin. Which makes a huge difference in how vital frequent inspections are.
Without that information, though, it’s my belief that we can’t say how well, or poorly constructed a structure might have been, even though it has failed. It may have been under-engineered, but I’m not about to assume it was.
And, again, given the way that corrosions like Stress Corrosion Cracking can quickly degrade metal components, I’m not going to give any kind of bye for skipping regular inspections, because the engineers should have designed something that would be maintenance free. We just don’t have that technology.
Actually, that may not be true. Remember that construction techniques then were a little lacking. They probably had very little more they could do toher than pile stuff up, and if there was an earthquake, flood, or storm, it prolly was gonna need one heck of a base. It was pretty common back then to massively overbuild rail bridges. Too new and too unknown. In any event, I suspect it was reinforced later on, although the original design was probably quite sturdy and efficient over time.
It’s not just construction techniques that were lacking - they didn’t have the knowledge we do about failure analysis to allow them to build more closely within tolerances.
For that matter, steel contruction of railroad bridges has a much poorer history if one goes back another 40 years to the 1840s. Those structures that are so over-engineered by modern standards are a response to some of the spectacular steel structure failures that happened when the Bessemer process started making steel competetive with other construction materials.
I’m not trying to fault their construction for being over-engineered. Consider the Brooklyn Bridge - because it was such a new technology, we now know that it’s incredibly over-engineered. (Though it was designed to be such. Just not quite to the extent that it has been proven to be, AIUI.) After the spectacular railroad bridge failures in the earlier part of the nineteenth century, engineers of the 1880s were trained to be very conservative. And even more so when dealing with new techniques.
We know more about how to analyze the stresses and strengths that new techniques may face, but we still have problems sometimes with going from prototypes to full-sized construction all the same. When I’m criticizing those older structures for being over-engineered, I am well aware I’m doing it with over a hundred years of advances in structural testing, materials science, and experience.
My criticisms about the designs being bad designs because they’re so over-engineered were meant to be taken within the context of current knowledge of the state of the art. At the time that they were built - I’m not prepared to say that the designers were incorrect in their decisions, based on what they knew then.
But I think it’s fair to say that comparing successful constructs from that era with those built with more thorough knowledge of materials and stresses isn’t a valid comparison. And a call to go back to those kind of margins isn’t sensible.
Though, like TheLoadedDog said - while 1000% safety factors might be excessive, a more hefty safety factor than the leanest allowed by code seems quite reasonable.