Collapse of the Fern Hollow Bridge(ntsb.gov)
ntsb.gov
Collapse of the Fern Hollow Bridge
https://www.ntsb.gov:443/investigations/Pages/HWY22MH003.aspx
115 comments
NTSB usually puts those videos in it's final reports, or as side footage on youtube if nothing is obviously graphic
Research Pennsylvania's Right-to-Know Law. There may be an avenue that would let you request copies of the video.
Very interested to hear the outcome of this investigation. As a Pittsburgh resident, it's pretty common knowledge that our ~450 bridges are not in great condition, and this just confirms it. The last inspection on this bridge was done in September of 2021 - Although it was determined to be in "poor" condition, it wasn't deemed unsafe. Less than 6 months later it collapses. How many more of our bridges are this close to collapse?
If I remember things correctly about 45,000 bridges across the US are in poor condition and the original Infrastructure Bill targeted 10,000 of them.
The Bill got watered down further.
There is simply too much infrastructure to maintain, and more and more stuff is being built every day with no realistic plan for long-term maintenance. It's a losing battle.
There is simply too much infrastructure to maintain, and more and more stuff is being built every day with no realistic plan for long-term maintenance. It's a losing battle.
Strong Towns makes the case that there is just too much infrastructure in the US and the level of sprawl that we are built at is economically unsustainable in the long run.
Except for a very generous interpretation of "the long run", I don't buy this. We pay more than enough money in taxes to maintain our infrastructure. The problem is governments misallocating and wasting funds.
Mostly to corporate subsidies labeled "defense" spending.
The world Strong Towns wants is emotionally unsustainable. Maybe there are people who can handle it, but I would go insane in the dense cities it suggests.
Let the people who like dense towns live there, and stop trying to tell the rest of the people how to live.
Strong Towns also tries to creates cities where no one from the outside ever comes in, since there's no way of getting there (no parking, not enough roads).
People in large cities also like to "get away" during the summer - but there will be nowhere to go in his world.
Let the people who like dense towns live there, and stop trying to tell the rest of the people how to live.
Strong Towns also tries to creates cities where no one from the outside ever comes in, since there's no way of getting there (no parking, not enough roads).
People in large cities also like to "get away" during the summer - but there will be nowhere to go in his world.
Nobody’s telling you can’t live in a rural area. Just don’t ask me to pay for a road and a water main out to reach you from the city. Get a Jeep and dig a well and move if the water dries up.
Why was it possible to build it, but now it is impossible to maintain it?
Maintaining things is not necessarily less costly or even viable, compared to building things.
Also, labor costs have gone up dramatically due to a variety of factors. Increased safety standards, less supply of labor relative to demand, increased liabilities due to tort laws, etc.
Also, borrowing from the future to build today is easy when population is exploding and you know everyone is having 3+ kids which will expand the tax base. That has not been true for quite a few decades now, with tax bases declining in many areas and political appetite for subsidizing those areas is waning, in my opinion.
Less future growth means more restrained borrowing today. There is also a significant and increasing amount of the country’s resources being spent on keeping old people alive that was not the case when all the old infrastructure was built.
Also, labor costs have gone up dramatically due to a variety of factors. Increased safety standards, less supply of labor relative to demand, increased liabilities due to tort laws, etc.
Also, borrowing from the future to build today is easy when population is exploding and you know everyone is having 3+ kids which will expand the tax base. That has not been true for quite a few decades now, with tax bases declining in many areas and political appetite for subsidizing those areas is waning, in my opinion.
Less future growth means more restrained borrowing today. There is also a significant and increasing amount of the country’s resources being spent on keeping old people alive that was not the case when all the old infrastructure was built.
Have there been no improvements to bridge building technology, that would make it cheaper today?
I assume there have been, but based on all the reported costs of building infrastructure, I concluded that any reductions in costs must have been greatly offset by increases in costs.
This one was especially bad -- I can't find the twitter post, but someone had snapped a picture in 2018 where a structural member had rusted completely through. The bridge should have been immediately shut down but was not.
To read more in general check out https://infrastructurereportcard.org/infrastructure-categori.... Bridges with rust is normal, but there is a replacement schedule.
To read more in general check out https://infrastructurereportcard.org/infrastructure-categori.... Bridges with rust is normal, but there is a replacement schedule.
That’s the one where it was unclear whether it was a concern because there was a bunch of more recent cabling around, and the agency responded with some sort of ticket number, yeah?
One problem is steel reinforced concrete is nearly impossible to detect rusting until it makes its way to the outside of a member. The ends of the bridge were reinforced concrete, so it's possible they just couldn't detect the problem and so didn't deem it unsafe.
IIRC some one traveled under this bridge last year and took photographs of several of the metal supports which were entirely rusted through and not connected to anything.
I saw those photos as well, and the presence of steel cables with turnbuckles to reinforce the structure lead me to believe that the damage was known and someone decided that the minimal reinforcement was adequate.
I suspect that if that was the primary cause of the collapse, the NTSB would have mentioned it directly already.
Either way, we'll know eventually.
I suspect that if that was the primary cause of the collapse, the NTSB would have mentioned it directly already.
Either way, we'll know eventually.
Which may have been fine if other supports were taking the load. Visibly rusted parts are easy to diagnose, thus if that particular part was unsafe it would have been quickly deemed as such. It could be that it contributed to the collapse, but that it alone wasn't enough to justify it as unsafe.
The most surprising the thing from the article is the posted weight limit of 26 tons. I'm no structural engineer but that seems very low to me for the size and length of the bridge? From the looks of the picture, shouldn't that bridge support like 5x to 10x that weight? A quick google shows that the average car weight is 4156 lbs [1]. So the bridge can only support roughly 5.5 cars before its over limit? And that is not considering common heavy vehicles likes semis, buses, etc.
And with auto industry going to toward EVs, vehicles are only going to get heavier, not lighter. The upcoming Hummer EV will be 9000 lbs [2] for example. This bridge seems awfully under-spec'd for its purpose. Someone please tell me that I am interpreting this number wrong.
[1]: https://www.bankrate.com/insurance/car/average-car-weight/ [2]: https://www.google.com/search?q=hummer+ev+weight
And with auto industry going to toward EVs, vehicles are only going to get heavier, not lighter. The upcoming Hummer EV will be 9000 lbs [2] for example. This bridge seems awfully under-spec'd for its purpose. Someone please tell me that I am interpreting this number wrong.
[1]: https://www.bankrate.com/insurance/car/average-car-weight/ [2]: https://www.google.com/search?q=hummer+ev+weight
I think the posted limit is supposed to be per vehicle.
As a side note, a 9000 lbs consumer grade vehicle is insanity.
I don’t inherently disagree agree with you but 9k lbs isn’t too far out of the range of normal passenger vehicle weight. But I would agree that many vehicles in the US and North America are probably oversized.
How do you define "Normal passenger vehicle"?
An Audi A6 weights 4500 lbs, Tesla Model S LongRange is 4800 lbs, Honda CRV is 3500 lbs, Honda Odyssey Minivan is 4600 lbs, Ford Explorer is 5000 lbs, even a Ford Expedition is "only" 5600 lbs.
What passenger vehicles are in the range of 9000 lbs?
An Audi A6 weights 4500 lbs, Tesla Model S LongRange is 4800 lbs, Honda CRV is 3500 lbs, Honda Odyssey Minivan is 4600 lbs, Ford Explorer is 5000 lbs, even a Ford Expedition is "only" 5600 lbs.
What passenger vehicles are in the range of 9000 lbs?
A full size pickup with passengers and cargo. IIRC my dodge 2500 is ~6000#, plus 2500# of cargo, your pretty much there.
A 2018 Ford F350 Super Duty dually is about 8000#, add at least 3000# of cargo, your already at 11k#.
A 2018 Ford F350 Super Duty dually is about 8000#, add at least 3000# of cargo, your already at 11k#.
That's not really a passenger vehicle though, it's a truck (it's right there in the name "pick up truck"). Just having more seats doesn't make a truck into a "passenger vehicle", my brother used to drive a 40,000 lb heavy truck that had a crew cab that seats 6, but no one would classify that as a "passenger vehicle".
It was so heavy that when he took it home, he couldn't drive it all the way home, he had to park it a half mile away and walk because there was a bridge with a 10 ton weight limit that he couldn't cross.
It was so heavy that when he took it home, he couldn't drive it all the way home, he had to park it a half mile away and walk because there was a bridge with a 10 ton weight limit that he couldn't cross.
I'd say most Americans see a pickup as a "passenger vehicle".
They're certainly licensed the same in my state.
They're certainly licensed the same in my state.
You don't actually need such a vehicle though. In EU you don't see trucks or many heavy vehicles like that at all.
Listen, I can haul sheet goods on the roof of any car all day long and he happy doing it.
But the problem is that YouPeople(TM) (as opposed to you personally) won't be happy about it. Instead of screeching about the environment you'd be screeching about safety. But it's not really about the environment or safety, it's about class. The fact of the matter is that moving any sizeable amount of goods (like some plywood for a garden shed, or a new stove, or similarly mundane things) with a car or crossover just doesn't pass for acceptable behavior for the slice of society that we're talking about here. People need more vehicle than they "need" for the same reason a 30yo finance professional "needs" a couple sets of nice clothes. It's what his peers expect from him. The quirky college professor can haul a sailboat on the roof of his prius and the tweaker won't be bothered for running scrap with a minivan but outside of that it's just not what "nice people" do (not that either of them care about the opinions of the kind of people who deride them). Meanwhile white collar people with three kids won't even shove them in a crossover once a week if they can avoid it. They'll commute in a 3-row SUV that costs twice as much to operate instead.
People buy crew cab trucks and 3-row SUVs because YouPeople(TM) expect them to "act their income" and they "need" the capability of these vehicles often enough to justify it.
But the problem is that YouPeople(TM) (as opposed to you personally) won't be happy about it. Instead of screeching about the environment you'd be screeching about safety. But it's not really about the environment or safety, it's about class. The fact of the matter is that moving any sizeable amount of goods (like some plywood for a garden shed, or a new stove, or similarly mundane things) with a car or crossover just doesn't pass for acceptable behavior for the slice of society that we're talking about here. People need more vehicle than they "need" for the same reason a 30yo finance professional "needs" a couple sets of nice clothes. It's what his peers expect from him. The quirky college professor can haul a sailboat on the roof of his prius and the tweaker won't be bothered for running scrap with a minivan but outside of that it's just not what "nice people" do (not that either of them care about the opinions of the kind of people who deride them). Meanwhile white collar people with three kids won't even shove them in a crossover once a week if they can avoid it. They'll commute in a 3-row SUV that costs twice as much to operate instead.
People buy crew cab trucks and 3-row SUVs because YouPeople(TM) expect them to "act their income" and they "need" the capability of these vehicles often enough to justify it.
> People need more vehicle than they "need" for the same reason a 30yo finance professional "needs" a couple sets of nice clothes. It's what his peers expect from him.
I'm afraid you're projecting your own issues on others...
I'm afraid you're projecting your own issues on others...
Wow.. toxic.. You people? My words and thoughts are my own. Never said you should haul sheets on your roof. That's your words. Have a nice day.
While I didn't reply with the same degree of hostility as the GP, I had the same emotional reaction to your comment. My immediate thought was "who are you to say what I 'need'?"
I'm self-aware enough to realize that this is because of a larger cultural struggle in the US between "rural" and "urban". It's not quite that simple, but that's a close enough approximation for the conversation at hand.
The rural people on the US feel like we are constantly fighting a system in which we have no voice. We're subject to regulations that we feel to be frankly ridiculous; regulations that get in our way, make our lives more difficult and expensive, and most of all... don't even serve the purpose for which they were ostensibly designed.
In that context, the GP's response to your comment is understandable.
I'm self-aware enough to realize that this is because of a larger cultural struggle in the US between "rural" and "urban". It's not quite that simple, but that's a close enough approximation for the conversation at hand.
The rural people on the US feel like we are constantly fighting a system in which we have no voice. We're subject to regulations that we feel to be frankly ridiculous; regulations that get in our way, make our lives more difficult and expensive, and most of all... don't even serve the purpose for which they were ostensibly designed.
In that context, the GP's response to your comment is understandable.
This is a common sentiment but it always makes me chuckle. People living in rural areas quite literally have more of a voice (as much as that counts for anything with political corruption) than people living in urban areas due to the Senate and gerrymandered congressional districts.
It was tongue in cheek/sarcasm. Point is people with the money to buy new buy more vehicle than they "need" because it is what society expects of them so in some sense they "need" it to meet the expectations of those around them.
> Point is people with the money to buy new buy more vehicle than they "need" because it is what society expects of them so in some sense they "need" it to meet the expectations of those around them.
I'm afraid that you are guilty of what psychology would call "projection". Unless you can back your views with hard facts. I have yet to meet anyone just blowing away $100k on a truck that don't NEED.
I'm afraid that you are guilty of what psychology would call "projection". Unless you can back your views with hard facts. I have yet to meet anyone just blowing away $100k on a truck that don't NEED.
> In EU you don't see trucks or many heavy vehicles like that at all.
It’s a side-issue, but I see this type of statement all the time about “Europe” and have to say, in Sweden - and even on the suburban streets of Stockholm - these enormous American pickups and SUVs are amazingly common (although most of them don’t go over the 3500kilo limit).
It’s a side-issue, but I see this type of statement all the time about “Europe” and have to say, in Sweden - and even on the suburban streets of Stockholm - these enormous American pickups and SUVs are amazingly common (although most of them don’t go over the 3500kilo limit).
They are not as common as in the US. And crucially, they are not (yet) a status symbol. Someone who can afford a vehicle like that as a daily driver (not a contractor) will get a huge-ass Merc or Audi instead.
Work vehicles in Stockholm are mostly small vans.
Work vehicles in Stockholm are mostly small vans.
> They are not as common as in the US
I'm not sure we're living in the same US ...
I'm not sure we're living in the same US ...
Top selling vehicles 2021 USA (https://www.caranddriver.com/news/g36005989/best-selling-car...)
1. Ford F-series
2. Ram pickup
3. Chevrolet Silverado
1. Volvo S/V60
2. Volvo XC40
3. Volvo XC60
> although most of them don’t go over the 3500kilo limit
I bet most not even go over 2000kg. My SUV is 1900kg (4k lbs) and is hybrid so has extra weight due to batteries. I think it's a very heavy car and considering downgrading again.
Cars over 4000 kg is straight insanity
I bet most not even go over 2000kg. My SUV is 1900kg (4k lbs) and is hybrid so has extra weight due to batteries. I think it's a very heavy car and considering downgrading again.
Cars over 4000 kg is straight insanity
Respectfully, you're wrong.
Sure, there are a lot of people who own trucks that don't use them as trucks on a regular basis - but there are a lot of people who do.
Sure, there are a lot of people who own trucks that don't use them as trucks on a regular basis - but there are a lot of people who do.
But what happens in the EU is not really relevant at all in this conversation, no?
It works as an example that you don't actually need them.
Please do not imply were dumb. We're not spending 100,000$ just to show off. We do need them, because we need to haul 2000-4000lb at a time over hundreds of miles and tow 5,000lb to 30,000lb on a regular basis. My biggest haul personally was about 20,000lb (of actual payload) over 500mi, and I regularly max out my 2,500lb capacity dodge 2500.
You ain't gonna move that shit with a Citroen C2.
Also, it's not just a matter of payload. The bigger wheelbase and larger tires make them much more drive able in snow or mud or ice which is common weather around. Small cars are a safety issue on black ice.
Btw, I'm a small player.
You ain't gonna move that shit with a Citroen C2.
Also, it's not just a matter of payload. The bigger wheelbase and larger tires make them much more drive able in snow or mud or ice which is common weather around. Small cars are a safety issue on black ice.
Btw, I'm a small player.
I don't think anyone has a problem with professionals using tools fit to task. (I certainly don't.) I just personally don't want to have to walk or bike on streets where trucks are moving a combined weight of 5 or 6 tons at high speeds. I think this could be solved with smarter street/highway design, which would also help drivers get from A to B more efficiently.
And FWIW, I grew up in rural Indiana (USA), soybean and corn country. It's definitely not just professionals driving these vehicles. Actually I'd say most trucks on the streets growing up were NOT used by professionals, the real farm trucks were often barely street legal and could never seem to get past 30-40 mph with a load (or without heh).
And FWIW, I grew up in rural Indiana (USA), soybean and corn country. It's definitely not just professionals driving these vehicles. Actually I'd say most trucks on the streets growing up were NOT used by professionals, the real farm trucks were often barely street legal and could never seem to get past 30-40 mph with a load (or without heh).
If you're using a truck to work and it fits the purpose then there is no need to feel it's been directed towards you.
It works as an example that _people in the EU_ don't seem to need them.
Only urbanites don't need them... until they do. Plenty of people in Europe need pickups.
I'm not an urbanite, but on the rare occasion I need a pickup truck, I rent one. I don't like owning things I only need occasionally, I use our communities tool lending library too when I need a tool for a project.
Just as if you could plan which tool you'd need for a job... You'd be surprised how quick you can go from using a ratchet, to an impact, to an air driven 3/4" impact, to requiring an oxy-acetylene torch for a given job...
How about we agree that we just don't have the same lifestyle ?
How about we agree that we just don't have the same lifestyle ?
Only when you're living a EU urbanites lifestyle. And who the fuck are you to speak in term of "need" ?
You don't need an iphone when a 10 that's old piece of crap hardware does the same job (albeit much less efficiently).
You don't need an iphone when a 10 that's old piece of crap hardware does the same job (albeit much less efficiently).
What do the people who currently have the trucks use them for?
A lot of them just use them for driving to places that they could do in a car. How many truck you see driving which are completely empty? Or how many you see who are transporting stuff that could easily have been done in a van?
That's complete bs, see my comment above. Pickups are much more flexible than vans.
The problem is the insurance model which insure the vehicle rather than the driver. Thus why some people daily drive their pickup because maintaining another beater is too much cost.
The problem is the insurance model which insure the vehicle rather than the driver. Thus why some people daily drive their pickup because maintaining another beater is too much cost.
Hauling / towing heavy / bulky shit.
Every now and then their 5' 100lb wife will use that truck to go for groceries and then you'll see them there, because you have no life in the real world, and you'll judge them based on that single interaction alone.
Meanwhile, the next day, her hubby and the family will tow an 8000lb boat to enjoy the lake, and heck they can even stop at the hardware store pick up a couple 1000lb of concrete / 2x4 for their home improvement projects.
I've personally saved a few grands this year in various fees alone by being able to haul shit and do DIY home improvements.
But sure, that's only for social grand-standing...
Every now and then their 5' 100lb wife will use that truck to go for groceries and then you'll see them there, because you have no life in the real world, and you'll judge them based on that single interaction alone.
Meanwhile, the next day, her hubby and the family will tow an 8000lb boat to enjoy the lake, and heck they can even stop at the hardware store pick up a couple 1000lb of concrete / 2x4 for their home improvement projects.
I've personally saved a few grands this year in various fees alone by being able to haul shit and do DIY home improvements.
But sure, that's only for social grand-standing...
In the EU you need a goods vehicle (truck) license to drive a vehicle + contents weighing more than 3,500kg (7,700lbs). Even most RVs here come well under that limit so you don't need a special license.
Yes, it is. I drive a 1988 Suburban 4x4 with a solid front axle, leaf springs, and all the old school heavier construction. With my fat lard butt in it, it's just under 6000lbs.
9000 lbs vehicles require a special licence to drive in the EU.
Accident safety ratings are going to have to be reinvented if heavy SUV EVs continue down this path. A Honda civic weighs 1/3 of this!
Weight limits are per-vehicle.
Imagine having to size up the other vehicles before crossing a bridge instead of just worrying about yourself.
Like playing the "guess your weight" game with everyone else piling into an elevator
[deleted]
Btw, 1 ton = 2000 lbs, not 1000.
As other people mentioned, it's per vehicle, so they multiply the maximum number of vehicles the bridge can hold at once.
Likely derated with time; a lot of bridges are given lower capacity as they wear out
Animation of the collapse and causative factors:
https://www.youtube.com/watch?v=zKfmEBcxs8A
https://www.youtube.com/watch?v=zKfmEBcxs8A
This video doesn’t start with “hello I am grady and this is practical engineering”, it’s unwatchable (also the sad / doomy music is distasteful, and so is claiming knowledge of causative factors when the incident is under active investigation).
> 447-foot-long bridge
> The posted weight limit on the bridge was 26 tons.
Is it just me or does this weight to length limit seem incredibly low? That articulated bus empty likely weighs 20 tons. An artic bus plus a few cars is already well over the 26 ton limit. I'm sure this bridge has also seen a fair share of truck abuse as the abysmal weight limit combined with the likelihood that truckers only see the weight limit once they're at the bridge with no way to turn around and no easy bypass route so they say screw this and drive their >26 ton rig right over it.
> The posted weight limit on the bridge was 26 tons.
Is it just me or does this weight to length limit seem incredibly low? That articulated bus empty likely weighs 20 tons. An artic bus plus a few cars is already well over the 26 ton limit. I'm sure this bridge has also seen a fair share of truck abuse as the abysmal weight limit combined with the likelihood that truckers only see the weight limit once they're at the bridge with no way to turn around and no easy bypass route so they say screw this and drive their >26 ton rig right over it.
Complete speculation based on reading the linked report:
The bridge suffered a fatal compromise but stood with light traffic. Until some combination of speed and weight of the bus pushed it over the edge. Something happened in the minutes or hours before the collapse and it was doomed to fall.
The bridge suffered a fatal compromise but stood with light traffic. Until some combination of speed and weight of the bus pushed it over the edge. Something happened in the minutes or hours before the collapse and it was doomed to fall.
The weird thing about it all is that this bridge is very heavily trafficked during rush hour. Occasionally, traffic even backs up to the bridge.
I'm really curious what could have happened to cause it to collapse so catastrophically when it withstood far more traffic just ~12 hours earlier.
I'm really curious what could have happened to cause it to collapse so catastrophically when it withstood far more traffic just ~12 hours earlier.
Perhaps it had been in a slow collapse for awhile and the 'point load' of the heavy bus in that moment caught it just right. There are pictures from several years ago of major structural crossmembers completely rusted through to the point they weren't even attached;
https://twitter.com/gpk320/status/1078885655634157569
https://twitter.com/gpk320/status/1078885655634157569
Just from that picture alone, the bridge should have been condemned long ago.
The odd thing to me is that a bus route is regular. I would bet that a bus this size runs on that bridge fairly regularly throughout the day; a bendy-bus is never used on a route that doesn’t need it, it’s harder to drive and uses more fuel.
I could imagine that having periodically changing loads like rush hour traffic could cause a critical failure state. The slow flexing between day and night eventually causing something to deform/crack/shift to the point that the next big traffic load causes a collapse.
If prior NTSB reports are any predictor, we'll eventually learn all about the confluence of things that led to the collapse.
If prior NTSB reports are any predictor, we'll eventually learn all about the confluence of things that led to the collapse.
It was a nasty night, weather wise, if I recall.
Perhaps a freeze thaw cycle that split one to many bolts?
Perhaps a freeze thaw cycle that split one to many bolts?
Time, weather and lack of maintenance.
From the article, the posted weight limit was 26 tons. A quick google search ("bus weight") shows that buses can easily exceed that limit and the bus on the bridge was a "double" bus.
Maybe the bus wasn't supposed to cross that bridge?
Maybe the bus wasn't supposed to cross that bridge?
I seem to remember that bridge weight limits aren’t as clear as just a number like that. I’d have to look at the DOT site, and I’m on my phone and too lazy right now. But I’d be willing to bet that a limit is per axle with other factors multiplied in for how close tandem axles are. It’s more about weight distribution than total weight. The posted signs are meant to be read by truckers who know the formulae.
A couple days before the collapse, there was a heavy snowfall. Deep heavy snow. I calculate that the weight of the snow was about 200 tons.
How did you calculate that? I don't know how much snow there was, but 10 inches of snow has around 1 inch (2.5cm) of water.
The bridge was 136m long, by about 13m wide and assuming 2.5cm of water content:
136m * 13m * .025m = 44 m^3 of water, or 44,000 kg, roughly 50 US tons.
A newspaper report said there was a light snow with 1 or 2 inches accumulated since 2am the morning of the collapse. Photos of the scene showed grass and small rocks on the ground visible through the snow, so it doesn't seem like there was a lot of snow on the ground. Even if there was heavy snow a couple days before the collapse, most of it would have been plowed off, I don't see big berms of snow on pictures of the collapse.
So if there was just a couple inches of snow, then it was probably closer to 10 tons worth of snow.
https://www.cnn.com/2022/01/28/us/pittsburgh-bridge-collapse...
The bridge was 136m long, by about 13m wide and assuming 2.5cm of water content:
136m * 13m * .025m = 44 m^3 of water, or 44,000 kg, roughly 50 US tons.
A newspaper report said there was a light snow with 1 or 2 inches accumulated since 2am the morning of the collapse. Photos of the scene showed grass and small rocks on the ground visible through the snow, so it doesn't seem like there was a lot of snow on the ground. Even if there was heavy snow a couple days before the collapse, most of it would have been plowed off, I don't see big berms of snow on pictures of the collapse.
So if there was just a couple inches of snow, then it was probably closer to 10 tons worth of snow.
https://www.cnn.com/2022/01/28/us/pittsburgh-bridge-collapse...
We had almost 8 inches of heavy snow. But Still my math must have been off (did in my head). Doing again I get
10 lb/ft * 450ft * 45ft / 2000 = ~100 tons
10 lb/ft * 450ft * 45ft / 2000 = ~100 tons
This is a failure mode already accounted for in determining the posted weight limits.
Looks like the bus named in the NTSB report is 39000-45500 lb, so under the bridge's weight limit: https://en.wikipedia.org/wiki/New_Flyer_Xcelsior
Your speculation is that the bridge suffered a failure prior to the failure of the bridge? Thanks for the insight I guess.
I think you are right, something happened.
It was probably me. I really need to get back on my diet tbh
I'm assuming Corten steel would never be used structurally nowadays?
I know it's sometimes used as a fancy cladding material, but I'm assuming thats all?
I know it's sometimes used as a fancy cladding material, but I'm assuming thats all?
Poor maintenance, bad decisions to remove part of the bridge support instead add another strip or just weld it again and ... salt in the roads that maybe end in the water or drip from the road above. Corten steel is very durable, add salt and this is a different question.
Corten steel is often used structurally, even in recent structures, because the idea is that the rust forms a protective layer. As long as water is not allowed to pool, it shouldn't rust through.
Some pictures of Corten steel structures:
https://www.corten.com/what-is-corten-steel.html
I'm familiar with the structures shown in that link. The U.S. Steel Tower seemed to be holding up well when I worked there, although looking out some windows you could see slightly worrying depressions in the steel beams where water had pooled over the years, and the steel had rusted away a bit (leading to more pooling). The Delaware footbridge was constructed much more recently and still looks new - no signs of wear that I've noticed walking across it.
If Corten steel is not durable enough for structural use, we're in trouble. It's used quite a bit, at least in the northeast.
Some pictures of Corten steel structures:
https://www.corten.com/what-is-corten-steel.html
I'm familiar with the structures shown in that link. The U.S. Steel Tower seemed to be holding up well when I worked there, although looking out some windows you could see slightly worrying depressions in the steel beams where water had pooled over the years, and the steel had rusted away a bit (leading to more pooling). The Delaware footbridge was constructed much more recently and still looks new - no signs of wear that I've noticed walking across it.
If Corten steel is not durable enough for structural use, we're in trouble. It's used quite a bit, at least in the northeast.
before picture of bridge from below on googlemaps
https://maps.app.goo.gl/prRF494MztYAhXoW6
https://maps.app.goo.gl/prRF494MztYAhXoW6
TLDR is that there is no obvious cause yet. The report says that there were no failures in the fracture critical components.
There is no information: on state, maintenance, geologic activity, or initial failure point.
While interesting any claim of cause is at absolute best an “educated guess”.
There is no information: on state, maintenance, geologic activity, or initial failure point.
While interesting any claim of cause is at absolute best an “educated guess”.
The NTSB (almost?) never determines a cause in the preliminary report, even when the cause is obvious. Example: https://www.ntsb.gov/investigations/Pages/HWY22FH001.aspx
my comment was mostly because there was already one thread with people making statements about cause of the failure based on this report :D
Interesting. I guess that spar wasn't critical https://www.post-gazette.com/local/city/2022/01/28/pittsburg...
My vague recollection from my first year engineering course, that I dropped before failing, almost 20 years ago (caveat train! Choo choo!) is a failure critical component is a component that if failing would trigger a complete structure failure.
There are parts of bridges where any failure would be expected to cause complete collapse, like the cracked beam on the Hernando de Soto bridge (happily that span turned out to not actually be critical). But as the Hernando de Soto bridge showed you can have a complete failure of a major structural element without a collapse (in this case we’re lucky that accidentally happened).
So if the report says that none of the instant fail section were responsible I’m going to trust that.
There are parts of bridges where any failure would be expected to cause complete collapse, like the cracked beam on the Hernando de Soto bridge (happily that span turned out to not actually be critical). But as the Hernando de Soto bridge showed you can have a complete failure of a major structural element without a collapse (in this case we’re lucky that accidentally happened).
So if the report says that none of the instant fail section were responsible I’m going to trust that.
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I wonder if maintenance schedule and state information should be gathered in a public database. I know US has thousands of entities of infrastructure but some manpower and some tablets is all you would need.
You mean like the National Bridge Inventory (https://www.fhwa.dot.gov/bridge/nbi.cfm)?
Money is the limiting factor. Tax dollars are already stretched thin. In many areas of the country infrastructure maintenance is at unsustainable levels with no easy solution.
You cant squeeze blood from a stone.
You cant squeeze blood from a stone.
Except the stone in this case is absolutely dripping with blood being slurped up by fat scavengers and building aircraft carriers (because we NEED 12 of them of course) while some asshole wags their finger at us and tells us this pinch of sand is all we can afford.
I take your point in good spirit, but there may be an argument to be made that military power is a net asset. But it's beside the point of my original comment. Local infrastructure budgets are not equipped to keep up with the demands.
It will be interesting if the result of this study is that the NTSB has to update their concept of fracture-critical components.
A "fracture critical" component is by definition a component that will cause a structure to collapse should it fail :D
We know what that "fracture critical" components of a structure through analysis of the design. So what the NTSB is saying here is that none of the components of this bridge that were identified as being fracture critical are the cause of failure.
Of course that doesn't mean there wasn't a single component failure, it is possible that there was an error in the analysis and a fracture critical component was not identified. Alternatively an error in construction could result in weaknesses in the structure leading to more fracture critical components.
It's also possible there were existing failures in non-fracture critical components that had not been detected, in which case you are getting closer and closer to every component being critical.
We know what that "fracture critical" components of a structure through analysis of the design. So what the NTSB is saying here is that none of the components of this bridge that were identified as being fracture critical are the cause of failure.
Of course that doesn't mean there wasn't a single component failure, it is possible that there was an error in the analysis and a fracture critical component was not identified. Alternatively an error in construction could result in weaknesses in the structure leading to more fracture critical components.
It's also possible there were existing failures in non-fracture critical components that had not been detected, in which case you are getting closer and closer to every component being critical.
Yes, it's too early to tell.
> The bridge was an uncoated weathering steel, three-span...
The somewhat larger New River Gorge bridge is also made from that type of steel.[1]
[1] https://en.wikipedia.org/wiki/New_River_Gorge_Bridge
The somewhat larger New River Gorge bridge is also made from that type of steel.[1]
[1] https://en.wikipedia.org/wiki/New_River_Gorge_Bridge
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I hadn't thought about bus cameras capturing the collapse -- wonder if this'll ever be released (or leaked)?