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RE: Tornado Alley construction

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If you are NOT in a hurricane region or serious seismic region (i.e. West Coast), it is NOT basic stuff...not matter how much you or I think that maybe it should be.  Granted, anchor bolts (code minimum, which is something like 5/8" diameter at 4 or 6 ft on center) is basic stuff to some degree.  But, "hurricane" straps and hold-downs for shearwalls are DEFINITELY not in most of the country.  You would be suprised at some of the nasty looks you can get when you start including hold-downs because you had the NERVE to do a lateral analysis which then showed overturning on shearwalls.  Keep in mind that in many parts of the country, the only way an engineer might get any where close to a resisdential home being built is he/she is drunk from tasting some fine beers at the local pub on a Friday afternoon after a hard day of dealing with contractors <grin> and had his/her keys taken away and managed to stumble to that home on the way back to his/her home in a drunken stuper only to pass out in the front yard of that home being built...that or they just happen to drive past the home on the way home if they are like me and don't drink! <grin>
 
Regards,
 
Scott
Adrian, MI
-----Original Message-----
From: David Topete [mailto:d.topete73(--nospam--at)gmail.com]
Sent: Friday, June 06, 2008 5:15 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Tornado Alley construction

i don't disagree with you, Scott.  i think the shocking part of the article is that there are some builders that are including straps and J-bolts (embedded 6"-8") into footings, which is not necessarily mandated by the local bldg. code...  That stuff seems so basic...  Cro-Magnon even knew that(!)....

On Fri, Jun 6, 2008 at 2:06 PM, Scott Maxwell <smaxwell(--nospam--at)umich.edu> wrote:
That article kind of glances over the fact that it was an F1 tornado (a baby tornado on the Fujita Scale)...talking wind speeds that are 73 to 112 mph.  Now, I am not saying that I would want to be sitting there gawking at it as it headed for me, but in the grand scheme of things it ain't bad at all.  Add to that the fact that according to the article it never got closer than 3/4 of mile to "well built houses".  Thus, while the straps and anchor bolts (assuming installed properly and such) are a very good thing and I am certainly not suggesting that they are a bad I did, I would argue in the case outlined in the article it is a rather decent stretch to believe that they were the reason why there was no damage...the more likely reason was at the location of those homes, the winds speeds likely did not even get past the standard wind design speed for most of the country (90 mph) as dictated by code.
 
What the article neglects to mention is that _IF_ you are in the path of a serious tornado (say F3 or higher), there is likely not much one can do to prevent your home from being majorly trashed without doing MAJOR overdesign (i.e. forget wood...we are talking CMU or R/C with a significant amount of reinforcing...and even then there are situations where projectiles in very substantial tornados can still penetrate unreinforced CMU or concrete sections...take a look at the description of an F5 on this page: http://www.tornadoproject.com/fscale/fscale.htm ...note the part that says: "steel reinforced concrete structures badly damaged.") relative to current codes.  The current codes in the US don't come any where near designing homes to with stand direct hits of a tornado...and it is not just because tornado alley jurisdictions may not require straps or such.  The reality is that if an F3 or greater directly hits your home, all the straps in the world will likely not save it...they might mitigate the damage...it is debateable if they will mitigate the damage enough that the home would be savagable...but then strictly speaking, traditionally codes are not about the financial health or repairability of the structure but rather does the structure survive long enough and well enough so that your tushie is largely unharmed in any significant way.
 
I will say it again...I am not saying that straps and such are NOT a good idea...they are.  But, they should not give someone the false sense of security that if an F3 or greater tornado (maybe even a F2) that directly hits their house that their house will be unscathed or even minimally damaged...if you have a direct hit of an F3 or greater, your house is most likely toast, with or without straps.
 
Regards,
 
Scott
Adrian, MI
-----Original Message-----
From: David Topete [mailto:d.topete73(--nospam--at)gmail.com]
Sent: Friday, June 06, 2008 3:00 PM
To: SEAINT
Subject: Tornado Alley construction

 
It's amazing what uplift straps and sill bolts can do to prevent a house from flying away...  Granted, I'm out here in eqk country so tornadoes (or hurricanes) are not readily designed for.  But, with all the damage from tornadoes each year, especially through "Tornado Alley," wouldn't most building departments want to scrap the IRC and its prescriptive methods (if that is the code in effect) in favor of anchor bolts and roof straps??? 

--
David Topete, SE



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David Topete, SE