"We can build homes to survive tornadoes like Kentucky suffered. We just haven’t."
- Thread starter Saul Trabal
- Start date
Andy Wehrle
EF5
I'm mistrustful of any journalism that references the ASCE ever since their publication that strongly suggested the Joplin tornado was no stronger than EF3 simply because the majority of destroyed houses could have failed in winds less than 165 MPH.
rdale
EF5
AS
The ASCE is overseeing the EF scale damage indicator revision process, including such "trustable" names
as Jim LaDue, Don Burgess, Chuck Doswell, Al Gerard, Tom Grazulis, Ernie Ostuno, and more...
The ASCE is overseeing the EF scale damage indicator revision process, including such "trustable" names
as Jim LaDue, Don Burgess, Chuck Doswell, Al Gerard, Tom Grazulis, Ernie Ostuno, and more...Mike Smith
EF5
This is an interesting point. The NWS had JLN as an EF-5. But, its sister agency, NIST, had it as a lower-end EF-4.
I visited JLN after the storm and I was struck by the lack of EF-5 damage. I just assumed I had missed it or didn't visit the right part of the damage path.
Here is the key point: If JLN wasn't a five, just imagine the death toll if a similar storm reached actual EF-5 intensity.
It is terribly concerning that the issues w/r/t to the NWS's tornado warning program, one of which manifested itself in Mayfield the afternoon of December 10th, continue with no evident plan to fix them.
I visited JLN after the storm and I was struck by the lack of EF-5 damage. I just assumed I had missed it or didn't visit the right part of the damage path.
Here is the key point: If JLN wasn't a five, just imagine the death toll if a similar storm reached actual EF-5 intensity.
It is terribly concerning that the issues w/r/t to the NWS's tornado warning program, one of which manifested itself in Mayfield the afternoon of December 10th, continue with no evident plan to fix them.
Hi y'all! First post here but something in my small bucket of knowledge. We're going to see few EF-5's even with complete destruction evident. Why? The answer has a few facets, one of which is that the engineer's concept of a "well-constructed home" is almost never built. Building codes do require the "hurricane clips" for rafter/truss attachment, bolting/anchoring of sill plates, proper nail spacing of plywood sheathing, etc, and those things have the be right to pass your framing inspection. So the home this article speaks of ARE being built, and have been for over a decade across most of the nation. But engineers want to see other things not required by code; one big one is toe-nailed wall studs. In my 45 years of construction I've toe-nailed studs just twice. It just takes too long and costs too much when end-nailing is permitted, acceptable, faster, and cheaper. But if you want an EF-5 rating the damage survey engineers want to see that. And if you missed the spacing on a few plywood nails by 1/4", the inspector won't care (long as it's not a habit) because he and I both know that it really doesn't matter, but the survey engineer now writes off the whole house as not being suitable to assess EF-5 damage.
The damage assessment system is broken, with more than one thing needing to be rectified, but wood frame houses built today do have good storm survivability and as we all know there is a point where no wood-framed house is likely to survive simply because you then reach the limits of the wood itself. We can build stronger wood-frame houses without adding too much more expense, but that's a topic unto itself.
Phil
The damage assessment system is broken, with more than one thing needing to be rectified, but wood frame houses built today do have good storm survivability and as we all know there is a point where no wood-framed house is likely to survive simply because you then reach the limits of the wood itself. We can build stronger wood-frame houses without adding too much more expense, but that's a topic unto itself.
Phil
Drew Terril
Staff member
Phil, welcome to Stormtrack! I would like to address a couple of points though. I see you are in South Carolina, and yes, hurricane straps are required in coastal states, and on the plains as well. However, to my knowledge they are still not required in states like Kentucky and Tennessee, and definitely were not required when I was working construction in those two states at various points from 2006 to 2011.
With that said, I think you know even better than I do that all the hurricane straps and toe nails in the world mean nothing if the foundation is not adequate. And frankly, there is no scenario where CMU foundations are adequate against even an EF4. While I was not present in the areas of Kentucky that were impacted on 12/10, I worked in the industry long enough in that part of the country to know that CMU foundations make up the vast majority. Even of the poured concrete foundations, many are not of an adequate thickness, or reinforced with rebar. Of the pictures that I saw from the area, there was a good deal of work that I would have been embarrassed had it been my own. Others I saw revealed where corners were simply cut. And considering the people who participated in the survey process, who have an even better eye than I do because it's what they do for a living, I am content to trust their judgement, as they would have noticed the same things.
I don't think the system is "broken," as some are asserting, but I do think that the large amount of subjectivity under the previous scale is playing an immense role in the current perception. Could it have possibly been over 200mph? Sure. But even from pictures, the number of significant build issues was sobering to say the least.
With that said, I think you know even better than I do that all the hurricane straps and toe nails in the world mean nothing if the foundation is not adequate. And frankly, there is no scenario where CMU foundations are adequate against even an EF4. While I was not present in the areas of Kentucky that were impacted on 12/10, I worked in the industry long enough in that part of the country to know that CMU foundations make up the vast majority. Even of the poured concrete foundations, many are not of an adequate thickness, or reinforced with rebar. Of the pictures that I saw from the area, there was a good deal of work that I would have been embarrassed had it been my own. Others I saw revealed where corners were simply cut. And considering the people who participated in the survey process, who have an even better eye than I do because it's what they do for a living, I am content to trust their judgement, as they would have noticed the same things.
I don't think the system is "broken," as some are asserting, but I do think that the large amount of subjectivity under the previous scale is playing an immense role in the current perception. Could it have possibly been over 200mph? Sure. But even from pictures, the number of significant build issues was sobering to say the least.
Yes, I'm in SC but I do have a fair amount of experience building elsewhere and not only doing residential work, but industrial and commercial work as well. The last few ICBO building code revisions require those clips, and most places in the US build to one of the later (or the latest) code. And I do have friends elsewhere whom I discuss construction with in some depth as it's more than just a job to me but also something of a passion too. And studying tornadoes is something of a passion to me too. You're on target with the CMU foundations; those could be rather easily improved and in the best homes are being eschewed in favor of concrete these days which is much better in every regard. On the concrete reinforcement, that too has seen recent improvement due to updated codes. But to someone like me who has seen (and done) this on industrial jobs where it is critical, what we get in residential construction is almost a joke, both in design and especially implementation. So we do agree on many points here.
Yet I still know the entire system is broken,and here's why:
1- Building codes are both inadequate for this purpose and are not universal in scope.
2- Adherence to codes in construction is almost always minimal with best practice not even on the radar.
3- Inspection for code compliance in residential construction is universally done to a very poor standard.
4- Residential building design marginalizes structural strength in deference to almost every other aspect.
5- In damage surveys there is apparently no allowance for any deviance from listed building techniques even when they might be equal in effectiveness.
6- We're not allowing for corroborating evidence or non-listed evidence to play the part it should in damage surveying.
7- There is a lack of thoroughness in assessing every damage site with too much simply being overlooked intentionally.
There is room for improvement in all these areas, sometimes a vast amount of room. I can offer ample evidence to back up and prove all of my listed points here. But as is usual, our real problem is in these things being driven almost completely by money and inter-personal politics- poor motivations giving the poor results we get. Knowing something (actually a fair amount) of the structural strengths of wood and it's usage in home construction I know we reach it's inherent limitations at some point, and there's only so much we can do to help it achieve that level of structural strength. Can we build wood-framed homes to mostly survive say a low-end EF-4? I think so as long as there aren't any other factors involved such as major impact damage, although that will require a lot of changes in our approach. It can easily be done to EF-3 level without too many changes or added costs. And this can be done without significantly reducing livability of the homes so I can see no reason to not do this.
But it's not happening, and this is why I assert that the whole system is broken. A better system or the needed improvements on what we have now is the correct solution and can both fix the current problems as well as preventing similar problems in the future.
Phil
Mike Smith
EF5
Phil and Drew, thank you for the conversation. I've learned a number of things.
Having watched a number of YouTube videos from this outbreak...it surprized me seeing all those houses with cinderblock foundations(didn't even look like any were re-inforced cinderblock walls). Though I also have no idea how old those demolished homes were?
Out here in CO, foundations on homes are all done with poured reinforced concrete and have been for a long time. And atleast from the mid 80's on (can't say on older homes), anchor bolts set in the concrete. I pretty much just assumed that was standard practice everywhere! (though that said, I believe its more about the bad soils here than just storm resistance).
With the various YouTube videos I watched, in the comments there were plenty of "thats EF-5" ... My thought (and I'm not an expert in any way) was no that's EF-3, or maybe EF-4 at most.
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They certainly could build a home to withstand an EF-5:
Just build the whole outer structure (including the roof!) out of poured reinforced concrete! Bullet-proof glass on the windows, thick steel doors for any outside exit, etc.
Would it be "pretty"? nope.
Would the cost of such a home be something anyone except the rich could afford? I'm guessing not.
But simple fact is in theory it could be done.
And even then there would be the issue of large and/or high-speed debris strikes that could compromise the structure, even if it would withstand a direct hit by the tornadic winds themselves.
Out here in CO, foundations on homes are all done with poured reinforced concrete and have been for a long time. And atleast from the mid 80's on (can't say on older homes), anchor bolts set in the concrete. I pretty much just assumed that was standard practice everywhere! (though that said, I believe its more about the bad soils here than just storm resistance).
With the various YouTube videos I watched, in the comments there were plenty of "thats EF-5" ... My thought (and I'm not an expert in any way) was no that's EF-3, or maybe EF-4 at most.
--------------
They certainly could build a home to withstand an EF-5:
Just build the whole outer structure (including the roof!) out of poured reinforced concrete! Bullet-proof glass on the windows, thick steel doors for any outside exit, etc.
Would it be "pretty"? nope.
Would the cost of such a home be something anyone except the rich could afford? I'm guessing not.
But simple fact is in theory it could be done.
And even then there would be the issue of large and/or high-speed debris strikes that could compromise the structure, even if it would withstand a direct hit by the tornadic winds themselves.
rdale
EF5
That's not what is being discussed here - this is more for the EF2/3 type events.
House foundations vary greatly. The one I live in was built in 1928 on 16" square brick piers spaced about 12ft apart with those piers each sitting on a their own individual concrete footing about 2ft square. In between each pier was bricked in to form a non-bearing wall, but many similar homes here don't have anything but the piers, some of which reach 12ft high. Spooky to think about when considering wind resistance but like some of those old-and-now-gone homes in KY such as this was the standard when they were built.
I did some finish work in a new home built near here 4 years ago; the CMU stem walls in back are 22ft high and hollow. It's strapped down in lieu of anchor bolts, the straps are set in concrete only to the depth of the top block which meets even the current building codes in use there. It's not a whole lot better than where I live and there's no good reason for that. In the metro area I now work in there are 7 different building code administrative areas, one of which still has no building code inspection or enforcement with the other 6 using 4 different years of the ICBO building codes and each area having some variations on certain non-structural specifics. In the wider range I used to work in you can double those numbers. None require concrete stem walls nor even concrete-filled cells in the CMU stem walls for residential work. I can call a shipping container sitting directly on the ground a home in one place while next door on the same road in another district it has to be wood framing bolted to a properly made slab or stem wall foundation.
This is one reason why I assert that the entire system is broken. Our building codes are inconsistent, outdated, and allow for less than best practices in almost all of the US. A few places like CA and FL which deal with specific hazards are more sensible but the rest can be improved, sometimes greatly.
Drew Terril
Staff member
Phil, your subsequent comments have made it fairly clear to me that we were meaning different things when we talked about the "system" being broken. I believe you mean the system of how we build things, and on that I'm in agreement. I saw too many corners cut during my time in the industry. While there are specific needs for each region (for example, the shallow roof pitches needed in FL would not work in the upper Midwest where a foot or more of snow isn't uncommon), foundations in particular really need a set standard. My disdain for CMU foundations knows no bounds.
The "system" I was referring to NOT being broken was the EF scale and how tornadoes are rated. I just don't believe that we should change our methodology in assessing damage and lower thresholds just because we're not getting the ratings that we "think" we should be getting. Simply put, particularly in areas like Mayfield where the bulk of the homes are decades old and constructed using obsolete practices, "I think it *could* have had winds of over 200mph" is not enough IMO to justify an EF5 rating. I will readily admit though that my time in automotive and oilfield manufacturing, where much greater precision was required than even in construction, probably skews my thinking into needing more certainty.
The "system" I was referring to NOT being broken was the EF scale and how tornadoes are rated. I just don't believe that we should change our methodology in assessing damage and lower thresholds just because we're not getting the ratings that we "think" we should be getting. Simply put, particularly in areas like Mayfield where the bulk of the homes are decades old and constructed using obsolete practices, "I think it *could* have had winds of over 200mph" is not enough IMO to justify an EF5 rating. I will readily admit though that my time in automotive and oilfield manufacturing, where much greater precision was required than even in construction, probably skews my thinking into needing more certainty.
I appreciate your insight and experience, but the damage assessment is also broken as well. What would you think a tornado would be rated at if it wiped clean two or three adjacent old and poorly built homes while along that part of the track it also scoured out the ground to say a depth of over a foot? We clearly know such 'trenching' doesn't happen with an EF-2 or at best EF-3 which the home destruction would rate. But since we don't have any exact standards for ground scouring it will be noted but ignored, thus leaving an erroneous conclusion instead of one with the accuracy sought after. Exclusionary assessments will necessarily under-rate every situation.
Grazulis went back and rated tornadoes posthumously sometimes based on scant evidence. For the most part his ratings are generally accepted within one rank on the scale. If that's permissible there then it should also be permissible to similarly infer damage today based on non-standard criteria as he did. One of the main problems with the rating system is that it is attempting to be an exact science in a world of innacuracies. The reason for this lies mainly in the approach taken by those who survey and rate- engineers- who as we all know esteem accuracy over nearly anything else.
Thus my belief that we need to reposition the engineering input to fix the system since we know they are not going to change their approach. It was/is good that the NWS folks realized that they weren't qualified to deal with the engineering side of this and reached out to those who they thought could do it better. But they stopped there and forgot to assess themselves to see if indeed that change brought the best possible results. Thus my contention that every part of all the systems involved here are broken or need revision for us to go forward into better things.
Grazulis went back and rated tornadoes posthumously sometimes based on scant evidence. For the most part his ratings are generally accepted within one rank on the scale. If that's permissible there then it should also be permissible to similarly infer damage today based on non-standard criteria as he did. One of the main problems with the rating system is that it is attempting to be an exact science in a world of innacuracies. The reason for this lies mainly in the approach taken by those who survey and rate- engineers- who as we all know esteem accuracy over nearly anything else.
Thus my belief that we need to reposition the engineering input to fix the system since we know they are not going to change their approach. It was/is good that the NWS folks realized that they weren't qualified to deal with the engineering side of this and reached out to those who they thought could do it better. But they stopped there and forgot to assess themselves to see if indeed that change brought the best possible results. Thus my contention that every part of all the systems involved here are broken or need revision for us to go forward into better things.
Um ok.rdale said:
When I read this, I was going to ask that an admin delete my posts here...but seeing that there have been other replies to it I'm just going to leave it.
Rather than quoting your whole post (since its above), I kept just one line since its the main part I'm replying too..Phil R said:
I think this is something you are going to run into everywhere!
Here in CO for example, every county/city/town sets its own rules, so here too you run into inconsistent codes by location. (That said, what I do not know is if there is any sort of "statewide minimum", and then the county/city/town can impose stricter codes ontop of that.)
I find your descriptions interesting (and some actually a bit surprizing).
I'm not sure how this 'broken/inconsistent' system could even be fixed? Having a federal codes mandate (ie: a "one size fits all") approach certainly wouldn't work since there is such a great variance in what's needed from one location to the next.
Possibly a federal 'highly reccomended' of "you should follow IBC of no more than X years old" would be a good idea? While still allowing locations to set their own own rules?
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I could see CMUs being a viable option in extreme weather locations...if its done as a reinforced wall, I don't remember the specifics on this, but out of curiosity back at some point I'd looked up something to the effect of "reinforced cinderblock wall"..
The basics of it were that every so many blocks you have one section filled with concrete with rebar running vertically the height of the wall. And in addition every so many rows in height you have what amounted to a metal grid running horizantal the length of the wall (that or blocks with a notch designed for horizontal rebar to fit in). Doubt I could find the original articles I read, but it was interesting none the less. A quick google'ing & you should be able to find plenty of similar if interested.
Drew Terril
Staff member
Ground scouring is in fact factored in. Its been mentioned on more surveys than I likely can recall. Same with debarking of trees. These are contextual clues that surveyors look for when rating a tornado. Scouring, debarking, granulation of debris are all things that are looked for when surveys are done. To say that they're not considered is misleading at best, and certainly untruthful. Where most of the debate comes in is with distinguishing EF4 from EF5 ratings. I've seen very little debate of EF3s or lower that people think should have been rated higher. I have, however, seen considerable debate over F5s from the early period of surveying that may in fact have been overrated. Xenia in 1974 is one that comes immediately to mind that I've heard debate on.
The only one in the nearly two decades that I've been chasing that truly comes to mind that was rated EF3 and was highly debated is El Reno 2013. And that debate comes solely based on the 290ish mph rating that a DOW picked up from a subvortex. There was none of the ground scouring that one associates with EF4+ tornadoes. You could see patterns imprinted in flattened crops, but no real topsoil removal. I come from a farming family, and I know full well that crops has been planted within the previous three weeks before that event. There'd also been a good deal of rain before that day, so the soil was still soft and the roots of the crops would not have been deep enough to give significant resistance. So to assume it was stronger than an EF3 without ground scouring would be akin to a tornado in Dixie that didn't debark any trees.
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