Aaron Rider
Member
I agree with this simply because I think most average people occasionally remain silent to hide incompetent acts. We all, or most of us, did that when we were kids.
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slenker
Member
That definitely would fit with reality - Greenfield absolutely launched debris in the air, and was a very skinny tornado. It also speaks volumes to wedges that managed to get debris nearly up to 40k ft even though they were very wide and likely had a much more horizontal component to the wind vectors over a wide area. It also may be an acceleration thing, too, where since the tornado is skinnier it manages to accelerate things from rest with much more force than a larger and slower moving tornado.
I am still wondering how that house that Freddy McKinney rescued the family from with the Hawley tornado didn't get an EF4 rating. Aftermath photos show it was least partly bolted to its foundation.
slenker
Member
I would imagine they looked at the linger time, plus the fact that there must’ve been something wrong with the construction in general. But I do mostly agree, seems quite strange. The motion on that tornado looked quite violent too.
I noticed a lot of talk about mobile radar measured windspeeds and I wanted to give some food for thought.
Like I pointed out in the 5/19-5/22 thread about the Greenfield tornado, wind turbines were completely collapsed but the surrounding damage, such as trees nearby, seemed completely untouched. I believe that the winds within a tornado sometimes (perhaps not always?) expand outwards drastically and/or attain significantly stronger intensity just a few meters above ground level, perhaps as little as about 5-10 meters AGL.
If my theory is accurate then this would make DOW measurements somewhat useless unless a consistent calculation/formula can be made to estimate the windspeeds at a specific height in the tornado, which is unlikely.
It's also possible that tornadic windspeeds are higher than expected, since hurricanes rarely do similar damage from windspeeds alone despite them sustaining well over EF3 intensity winds for several minutes at times, although it's possible that hurricanes work differently, and that the damage caused by tornadoes are at the very least aided by the extremely rapid decrease in atmospheric pressure within them.
Again, this is just food for thought, and it's possible what I'm saying is completely and utterly wrong.
Like I pointed out in the 5/19-5/22 thread about the Greenfield tornado, wind turbines were completely collapsed but the surrounding damage, such as trees nearby, seemed completely untouched. I believe that the winds within a tornado sometimes (perhaps not always?) expand outwards drastically and/or attain significantly stronger intensity just a few meters above ground level, perhaps as little as about 5-10 meters AGL.
If my theory is accurate then this would make DOW measurements somewhat useless unless a consistent calculation/formula can be made to estimate the windspeeds at a specific height in the tornado, which is unlikely.
It's also possible that tornadic windspeeds are higher than expected, since hurricanes rarely do similar damage from windspeeds alone despite them sustaining well over EF3 intensity winds for several minutes at times, although it's possible that hurricanes work differently, and that the damage caused by tornadoes are at the very least aided by the extremely rapid decrease in atmospheric pressure within them.
Again, this is just food for thought, and it's possible what I'm saying is completely and utterly wrong.
EF scale windspeeds are defined at a ten metre height, so you're going to have to take it up with the guys who designed scale to argue about their windspeed-height relationship.
There's a simpler reason for the wind turbines collapsing - they're very large (80 m hub height in this case), stiff structures. The turbines couldn't be yawed for the tornado so the wind resistance of the blades was much greater and exerted at an angle outside the design specs. Note the diagram on page 62 of this Master's thesis - it shows that bending moments are much higher when the axis is not aligned with the airflow. In comparison most of the trees shown in the video at a similar distance are small and would be more flexible.
I haven't heard of the idea that the winds "expand outwards drastically", unless a vortex breakdown 'bubble' is located near the surface. Vortex models incorporate an assumption of zero speed at zero height, but while older models of tornadoes assumed tornado winds behaved like straight line winds in height profile, more recent examinations conclude this probably isn't the case, with higher speeds at lower heights. Kosiba and Wurman (2013) apparently showed the strongest winds at five metres.
The extra damaging nature of tornado winds is their complex structure - aside from their tight radius, they can change abruptly from horizontal to vertical, which is known as 'corner flow'. This is why they loft heavy objects. It also means they exert more and more varied stress on a structure than horizontal tropical cyclone winds. Static pressure drop is pretty much disregarded these days - even if a house is well sealed, a tornado can easily break windows. Recent writings I've seen that bring up the old idea that 'pressure drop exploded houses' point to dynamic pressure from winds penetrating a structure as being the likely cause for the apparent phenomenon.
Aaron Rider
Member
New here and no expert but what gets me is how it would all be so much better if they wouldn't do weird, arbitrary, or even screwy things with the construction aspect of the scale itself. From what I've read here, Vilonia is an obvious and egregious example, and Rochelle-Fairdale, New Wren, and several others are also probably good examples. Sometimes they just do bad surveys, of course. It seems like nearly a half dozen "EF4" tornadoes since Moore were underrated just in this sense.
I'm probably beating a dead horse.
I'm probably beating a dead horse.
You probably are, yeah. The general sentiment here is that the NWS needs to be more consistent and reasonable with the EF scale.
I will say, however, that I believe that New Wren was rated only an EF3 just because they missed the main damage path, not because of dumb construction stuff.
joshoctober16
Member
i think one of the biggest flaws of the EF scale is it almost seems like they don't want to fix / change there past mistakes.
and before you say there are too much tornadoes to look back into..... that's like saying there's to much asteroids in the solar system to catalog so lets not fix some stats on them asteroids.
and to make things simpler , at least relook at all the EF3-EF5 , and tornadoes that have deaths.
i know for new wren there shouldnt be a reason to keep it a EF3 , theres no reason for not having a high end EF4.
and i know some one will bring up the whole (they never went close to the damage) , well here's the thing, that means you cant be sure if it was well built OR POORLY BUILT , so its best to pick the middle ground not the low ground.
since i have no clue if it had hurricane wind resistant construction features i think new wren having a 195-200 mph rating would be fine.
and before you say there are too much tornadoes to look back into..... that's like saying there's to much asteroids in the solar system to catalog so lets not fix some stats on them asteroids.
and to make things simpler , at least relook at all the EF3-EF5 , and tornadoes that have deaths.
i know for new wren there shouldnt be a reason to keep it a EF3 , theres no reason for not having a high end EF4.
and i know some one will bring up the whole (they never went close to the damage) , well here's the thing, that means you cant be sure if it was well built OR POORLY BUILT , so its best to pick the middle ground not the low ground.
since i have no clue if it had hurricane wind resistant construction features i think new wren having a 195-200 mph rating would be fine.
Forgive the intrusion of someone not at all qualified to say anything intelligent in this thread, but today's tweet from the Japanese Meteorological Society caught my eye, if anyone is interested (even though it is Japan specific).
Translated: "[Press Release] (June 11, 2014) We will publish the "Report of the Study Group on the Assessment of Tornado and Other Wind Gust Intensity," which summarizes the process of formulating and improving the "Japanese Improved Fujita Scale (JEF)" and its technical guidelines, the "Guidelines for the Japanese Improved Fujita Scale."
Translated: "[Press Release] (June 11, 2014) We will publish the "Report of the Study Group on the Assessment of Tornado and Other Wind Gust Intensity," which summarizes the process of formulating and improving the "Japanese Improved Fujita Scale (JEF)" and its technical guidelines, the "Guidelines for the Japanese Improved Fujita Scale."
Sawmaster
Member
I'm placing this post here in response to a post made by member "A Guy" in the Significant Tornado Events thread because it's dealing with what I feel are the failings of damage surveying as it is done now. Thus it would be inappropriate there, but for context please read the discussion on that forum starting HERE
I just took a look at this report, and my conclusions regards it differ from yours- indeed these were almost all not "well-built" homes, but homes built in the usual manner. The house in the Hackleburg tornado used hardware far in excess of the standards seen here which was properly installed. The first thing I took away here was that during the interim between building and destruction the ASCE method of determining wind resistance of hardware changed- sometimes substantially. Wind forces from hurricanes lack vertical components and have little to no rapid atmospheric pressure drop adding to the destructive effect, thus these structural failures should not have occurred as easily as they did, and the blame for this aspect lies at the feet of the ASCE who always knew of these differences but hadn't previously considered them when testing for reinforcement hardware strength limits. An example of the short-sighted "check off the boxes" approach they take.
Next I noted that the commonly used engineered material OSB sheathing lost much of it's resistance to removal because of over-driven nails. This is the result of the ubiquitous use of nailguns and their being set to sink the nails deeply enough to avoid loss of time and effort needed to drive high fasteners flush manually. Again I find some fault in the engineering of these materials not compensating for common practices as they should be. If you engineer a product which only performs to specs when installed perfectly you're ignoring or are ignorant of what really goes on in the world around you. In other words a lack of common sense. In my career I've learned to use what I call "stupid proof" methods which ensure things are right, because if there's the possibility of a screw-up it will happen otherwise simply because of human nature. Having seen how fragile OSB is where the edge fastenings are, how easily fastener pull-through occurs with it, and how it loses much of it's strength if it gets saturated with moisture I don't like it at all compared to plywood or denser materials made in the same way like "Advantek" floor sheathing. The use of OSB results in much weaker houses IRL but it's cheaper than plywood and according to engineers at least equal to plywood in this application. Plywood is more "stupid-proof" and better tolerates the kinds of improper fastenings you normally see. And on the fasteners, gun-driven nails are both shorter and of smaller diameter than common nails and cement-coated sinkers which were used before the advent of nailguns becoming a thing. Once again this is allowed because in the perfect world of engineering tests, the gun nails were shown to have at least equal holding strength when my RL experience tell me otherwise.
And to not totally blame the engineers I must note that many usual building practices result in weaker structures, yet these practices are not disallowed by code. The fastener pull-out causing the separation of the bottom plate from an anchored floor system is commonly seen in wind damage, as is the separation of the double-plate from the top plate which H2.5 'hurricane ties' fasten to, thus allowing whole roofs to be easily lifted off of the wall structure. Also the ever-present pulling away of studs which are only end-nailed to the plate, which can easily be mitigated by having the wall sheathing begin at foundation level thus tying everything together without the use of toe-nailed studs. This approach also sees the sheathing overlap the double-plate-to-top wall-plate connection increasing greatly it's pull-away strength' Even in the report mentioning this, the "check the boxes" approach of damage surveying doesn't consider this, nor do building codes require it, mainly because engineers who develop building codes don't call for it. So the RL world instead places the sheathing from the bottom plate up, leaving two weak points above and below the sheathing because it's easier and faster to do it that way. Whenever you allow stupid to happen it will happen. When you're overly tightly focused on details (as engineering commonly is) you lose sight of the big picture and those things which can easily improve that.
There's a huge amount more in this report which exposes fault from all sides. It is the job of engineers to design better structures, materials, and methods which take into full account the real-world way things are done faults and all. IMHO it's the lack of actual building experience in the real world which disqualifies engineers from having the last say in these matters, because they don't understand that their methods and practices simply cannot be put to practical use IRL, so limit an EF-5 rating to only these nearly non-existant perfectly made homes is ludicrous and is only more proof that engineers are out of touch with reality and thus need to be relegated to a level where more realistic people supervise them and can overrule them when that's clearly called for.
I must also point out their conclusion that the expected performance matching the actual performance was mixed, even when factoring in faults. It must be said that they are the ones who originally set the standards and parameters and said what performance could be expected. Didn't they properly test these things before recommending them and stating what level of performance we could expect from them? Apparently not, or at best not well enough. I can see nothing different in their approaches to the subject matter today so IMHO they are not to be trusted or relied upon for these things until their approaches and methods improve.
I just took a look at this report, and my conclusions regards it differ from yours- indeed these were almost all not "well-built" homes, but homes built in the usual manner. The house in the Hackleburg tornado used hardware far in excess of the standards seen here which was properly installed. The first thing I took away here was that during the interim between building and destruction the ASCE method of determining wind resistance of hardware changed- sometimes substantially. Wind forces from hurricanes lack vertical components and have little to no rapid atmospheric pressure drop adding to the destructive effect, thus these structural failures should not have occurred as easily as they did, and the blame for this aspect lies at the feet of the ASCE who always knew of these differences but hadn't previously considered them when testing for reinforcement hardware strength limits. An example of the short-sighted "check off the boxes" approach they take.
Next I noted that the commonly used engineered material OSB sheathing lost much of it's resistance to removal because of over-driven nails. This is the result of the ubiquitous use of nailguns and their being set to sink the nails deeply enough to avoid loss of time and effort needed to drive high fasteners flush manually. Again I find some fault in the engineering of these materials not compensating for common practices as they should be. If you engineer a product which only performs to specs when installed perfectly you're ignoring or are ignorant of what really goes on in the world around you. In other words a lack of common sense. In my career I've learned to use what I call "stupid proof" methods which ensure things are right, because if there's the possibility of a screw-up it will happen otherwise simply because of human nature. Having seen how fragile OSB is where the edge fastenings are, how easily fastener pull-through occurs with it, and how it loses much of it's strength if it gets saturated with moisture I don't like it at all compared to plywood or denser materials made in the same way like "Advantek" floor sheathing. The use of OSB results in much weaker houses IRL but it's cheaper than plywood and according to engineers at least equal to plywood in this application. Plywood is more "stupid-proof" and better tolerates the kinds of improper fastenings you normally see. And on the fasteners, gun-driven nails are both shorter and of smaller diameter than common nails and cement-coated sinkers which were used before the advent of nailguns becoming a thing. Once again this is allowed because in the perfect world of engineering tests, the gun nails were shown to have at least equal holding strength when my RL experience tell me otherwise.
And to not totally blame the engineers I must note that many usual building practices result in weaker structures, yet these practices are not disallowed by code. The fastener pull-out causing the separation of the bottom plate from an anchored floor system is commonly seen in wind damage, as is the separation of the double-plate from the top plate which H2.5 'hurricane ties' fasten to, thus allowing whole roofs to be easily lifted off of the wall structure. Also the ever-present pulling away of studs which are only end-nailed to the plate, which can easily be mitigated by having the wall sheathing begin at foundation level thus tying everything together without the use of toe-nailed studs. This approach also sees the sheathing overlap the double-plate-to-top wall-plate connection increasing greatly it's pull-away strength' Even in the report mentioning this, the "check the boxes" approach of damage surveying doesn't consider this, nor do building codes require it, mainly because engineers who develop building codes don't call for it. So the RL world instead places the sheathing from the bottom plate up, leaving two weak points above and below the sheathing because it's easier and faster to do it that way. Whenever you allow stupid to happen it will happen. When you're overly tightly focused on details (as engineering commonly is) you lose sight of the big picture and those things which can easily improve that.
There's a huge amount more in this report which exposes fault from all sides. It is the job of engineers to design better structures, materials, and methods which take into full account the real-world way things are done faults and all. IMHO it's the lack of actual building experience in the real world which disqualifies engineers from having the last say in these matters, because they don't understand that their methods and practices simply cannot be put to practical use IRL, so limit an EF-5 rating to only these nearly non-existant perfectly made homes is ludicrous and is only more proof that engineers are out of touch with reality and thus need to be relegated to a level where more realistic people supervise them and can overrule them when that's clearly called for.
I must also point out their conclusion that the expected performance matching the actual performance was mixed, even when factoring in faults. It must be said that they are the ones who originally set the standards and parameters and said what performance could be expected. Didn't they properly test these things before recommending them and stating what level of performance we could expect from them? Apparently not, or at best not well enough. I can see nothing different in their approaches to the subject matter today so IMHO they are not to be trusted or relied upon for these things until their approaches and methods improve.
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