ornado impact force

huangyhg

tornado impact force
we've been looking at a few structural projects that involve building design for tornados.  i've done this in the past on a project using a report from texas tech university as a guide (much like using a geotechnical report on a project).  
we've also got the fema document 361, "design and construction guidance for community shelters". also have fema publication "national performance criteria for tornado shelters".  
the fema documents, and our local city code, all require a certain wind speed design (no problem); but go on and require a resistance to projectile forces such as a 2x4 wood projectile, 12 feet long, speeding into your walls or roof at some designated speed.  they never give criteria in terms of force of impact.
is there any similar resource out there that provides a force for this kind of impact.  fema 361 gives rough wall thicknesses, etc., but i would like to see some force guidance.
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you might check out the corps of engineers technical manuals at
thank you.