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Severe WX April 29-May 2nd, 2022 Severe Weather Threat

NWS offices really seem to only give tree damage an EF4 rating if there is at least some EF4 structural damage along the path. Even the Smoky Mountains tornado wasn't given an EF4 rating solely based on tree damage, the EF4 damage was a collapsed transmission tower.
 
MNTornadoGuy said:
In some cases, they have been rated EF4 such as the 2010 Bowdle SD tornado. Usually, the transmission towers have intense contextual damage around them and are ripped from their concrete mountings and flattened to the ground.
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The transmission tower that collapsed from the Bowdle tornado didn’t seem to have a lot of contextual damage around it if I remember right.
 
Inconsistency proves inaccuracy. Different people will have different perspective, but unless there's factors we don't know about involved then this is the same DI meaning that one or the other is in error. People can make mistakes, and as long as they're fixed with no one coming to harm from any of it I'm good with that. I'm not good with known errors going unrectified.


And indeed I have made an error myself regards this:
eric11 said:
I was curious why they labeled the John's Animal Pet office as a MBS? I think it's more like a barn actually
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On looking into things deeper this WAS a metal building, just one unlike what I'm unfamiliar with. This was made of strips of curved corrugated metal, the left and right connecting at the top to form an arch. To gain length you add more strips. The end result is something like a unibody (monocoque) car frame where the shape is the strength. Being relatively thin and relative light compared to it's surface area it's no wonder that it was ripped from it's ground attachment and flung somewhere past the view of the pictures. Once the first strip began pulling loose it added to the windload of the next strip which then released and so on, till it was all gone. That same process also weakened it as it occurred. To explain what seems like roof truss parts is that they are truss-type construction but for end walls, not the roof. Most likely came with the building kit.

I think I was close to target on the failure steps I originally mentioned with end walls failing first, but TBH I don't know how the ground-level fastening is done with that or the metal panels. I do know that most strength would be lost once the shape was compromised. So I offer my humble apologies for my error and promise it won't happen again.

Phil
 
Sawmaster said:
Inconsistency proves inaccuracy. Different people will have different perspective, but unless there's factors we don't know about involved then this is the same DI meaning that one or the other is in error. People can make mistakes, and as long as they're fixed with no one coming to harm from any of it I'm good with that. I'm not good with known errors going unrectified.


And indeed I have made an error myself regards this:

On looking into things deeper this WAS a metal building, just one unlike what I'm unfamiliar with. This was made of strips of curved corrugated metal, the left and right connecting at the top to form an arch. To gain length you add more strips. The end result is something like a unibody (monocoque) car frame where the shape is the strength. Being relatively thin and relative light compared to it's surface area it's no wonder that it was ripped from it's ground attachment and flung somewhere past the view of the pictures. Once the first strip began pulling loose it added to the windload of the next strip which then released and so on, till it was all gone. That same process also weakened it as it occurred. To explain what seems like roof truss parts is that they are truss-type construction but for end walls, not the roof. Most likely came with the building kit.

I think I was close to target on the failure steps I originally mentioned with end walls failing first, but TBH I don't know how the ground-level fastening is done with that or the metal panels. I do know that most strength would be lost once the shape was compromised. So I offer my humble apologies for my error and promise it won't happen again.

Phil
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Phil, is it more impressive to bend or snap anchorage bolts on a weaker structure or a well-built structure?Snapping of anchor bolts has always seemed impressive to me but maybe it isn’t all that impressive.
 
MNTornadoGuy said:
NWS offices really seem to only give tree damage an EF4 rating if there is at least some EF4 structural damage along the path. Even the Smoky Mountains tornado wasn't given an EF4 rating solely based on tree damage, the EF4 damage was a collapsed transmission tower.
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I swear the summary for that one (NCDC or maybe elsewhere) mentioned that the tree damage was at least part of the basis for EF4.

Also NWS Wilmington actually deemed the structural damage at the Rivers Edge Apartments to be EF4, which has always struck me as a bit odd. The apartments were heavily damaged, but compared to other events, they didn’t sustain damage consistent with other apartment buildings that sustained EF4-rated damage. Personally, I don’t see it, but I’m not an engineer. From what I saw, it looked like the worst winds were in the woods behind the complex, along the river.

But yeah, it does usually seem like there needs to be structural damage within the vicinity for EF4 tree damage. With that said, that small patch of woods that sustained extreme debarking near Bassfield, MS wasn’t within the immediate vicinity of any major structures irrc, and they still gave the debarking an EF4 rating.
 
Shakespeare 2016 said:
Phil, is it more impressive to bend or snap anchorage bolts on a weaker structure or a well-built structure?Snapping of anchor bolts has always seemed impressive to me but maybe it isn’t all that impressive.
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Well here we have to begin considering the steel they're made out of, how threads are made, and any post-formative heat-treatment or annealing done.

There's actually standards for all this but my experience with them, especially in very recent times, leads me to suspect that the ones used in residential work are not all the same. My very unscientific "test" of laying them on concrete and giving them a whack from my hammer shown me some dent more easily than others, and personally I believe the issue comes from the fact that most hardware now comes from China where quality control may not be so good.

Think the failure process through. If a bolt, nut, and washer remain intact then the wood must have failed first. If the bolt broke, then it could have been the weak point and the plate might have stayed put with stronger hardware. For that to become known you'd have to test the remaining portion of the bolt to assess it meeting the standards. What I'd find most impressive would be to find the bolt intact, bent or not, but with the metal stretched and drawn thin which would mean the wood failed first but that it took a lot of pressure before failing.

tldr: intact bolts indicate adequate bolt strength, broken one's don't.

Phil
 
buckeye05 said:
But yeah, it does usually seem like there needs to be structural damage within the vicinity for EF4 tree damage. With that said, that small patch of woods that sustained extreme debarking near Bassfield, MS wasn’t within the immediate vicinity of any major structures irrc, and they still gave the debarking an EF4 rating.
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This shows my points. If tree debarking is a valid indicator then contextual damage needn't be considered. If contextual damage is deemed a necessary adjunct, then where are the specifications of what the extent of that context is? "Nearby" and "same area" are vague and subject to interpretation- exactly how far does that extend? Thus the context is imprecise and inherently inaccurate. That means they are actually subjective criteria, and if you're going to allow subjective criteria here, why not with other DI's and factors too?

Both methods have their drawbacks, easy to see that with being subjective where the drawbacks are obvious. In Mayfield (and probably true in Andover too as I haven't seen all the pics and details yet) we had properly bolted slabs swept clean with the plates pulling away with the wall, yet a higher rating was denied because the studs were end-nailed, yet if the plates pulled away with the wall that indicates there was adequate strength of that connection whether it was toe-nailed or not. Now we see the drawbacks of having a supposedly 'scientific' method of assessment leading to inaccuracy.

Not trying to argue with anyone but rather I'm trying to show that part of the problem of having best accuracy in damage surveys at least partially lies in the approach being taken to the whole matter, not just the details. The depth of thought needed isn't being applied correctly or perhaps isn't being used at all.

Phil
 
Sawmaster said:
This shows my points. If tree debarking is a valid indicator then contextual damage needn't be considered. If contextual damage is deemed a necessary adjunct, then where are the specifications of what the extent of that context is? "Nearby" and "same area" are vague and subject to interpretation- exactly how far does that extend? Thus the context is imprecise and inherently inaccurate. That means they are actually subjective criteria, and if you're going to allow subjective criteria here, why not with other DI's and factors too?

Both methods have their drawbacks, easy to see that with being subjective where the drawbacks are obvious. In Mayfield (and probably true in Andover too as I haven't seen all the pics and details yet) we had properly bolted slabs swept clean with the plates pulling away with the wall, yet a higher rating was denied because the studs were end-nailed, yet if the plates pulled away with the wall that indicates there was adequate strength of that connection whether it was toe-nailed or not. Now we see the drawbacks of having a supposedly 'scientific' method of assessment leading to inaccuracy.

Not trying to argue with anyone but rather I'm trying to show that part of the problem of having best accuracy in damage surveys at least partially lies in the approach being taken to the whole matter, not just the details. The depth of thought needed isn't being applied correctly or perhaps isn't being used at all.

Phil
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On the EF-kit there is this one apartment in Joplin from 2011 that was rated EF2 even though only parts of the roof were peeled or somewhat torn off. I rated it EF1 but maybe there was something I was missing.
 
Sawmaster said:
This shows my points. If tree debarking is a valid indicator then contextual damage needn't be considered. If contextual damage is deemed a necessary adjunct, then where are the specifications of what the extent of that context is? "Nearby" and "same area" are vague and subject to interpretation- exactly how far does that extend? Thus the context is imprecise and inherently inaccurate. That means they are actually subjective criteria, and if you're going to allow subjective criteria here, why not with other DI's and factors too?

Both methods have their drawbacks, easy to see that with being subjective where the drawbacks are obvious. In Mayfield (and probably true in Andover too as I haven't seen all the pics and details yet) we had properly bolted slabs swept clean with the plates pulling away with the wall, yet a higher rating was denied because the studs were end-nailed, yet if the plates pulled away with the wall that indicates there was adequate strength of that connection whether it was toe-nailed or not. Now we see the drawbacks of having a supposedly 'scientific' method of assessment leading to inaccuracy.

Not trying to argue with anyone but rather I'm trying to show that part of the problem of having best accuracy in damage surveys at least partially lies in the approach being taken to the whole matter, not just the details. The depth of thought needed isn't being applied correctly or perhaps isn't being used at all.

Phil
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I always have a feeling that all contextual should be counted just to improve the accuracy because no indicator is impeccable, including structures.
We now have known that most of houses in US can not sustain EF5 wind or even Mid range EF4 winds. And in many occasions, the complete construction details picture of the house was missed. Damage survey article of Moore 2013 claimed part of sill plates moved and bolts bent should be regarded as one of EF5 feature and we now tend to think this was not accurate as well.

Almost equally important, houses are too small for many tornados. Even If a tornado encountered a really well built house, we don't know If the strongest part of the vortex hit the house. It can even just jump through the house so we can find almost intact house in the core of EF5 tornado like Hackleburg.

In contrast occasion, the strongest part of vortex can hit the absolute weak point of the house and I think this's the reason overall contextual damage didn't match up with the construction damage in some cases like Newnan GA.
 
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