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RE: tornado alley

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It is difficult to directly assign a performance level objective to the current codes because they are not performance-based.  However, take a look at ASCE 7, Section 1.4 (“General Structural Integrity”), where it states that the intent of this loading standard is to provide sufficient continuity, redundancy, and ductility to “resist loads without collapse.”  Additionally, the commentary section of SEAOC’s “Blue Book” states that structures designed and built according to the requirements and prescriptions of the code should be able to “resist collapse” when subjected to a major earthquake (from the 1999 edition).  “Collapse Prevention” is commonly identified as the lowest acceptable level of performance for any structure, and since the current codes specify minimum regulations only, then this must be the target level of performance.  I believe, however, that in reality we are closer to a “Life Safety” level of performance … IMHO.


Dave K. Adams, S.E., P.Eng.

Lane Engineers, Inc.

Tulare, CA






From: Scott Maxwell [mailto:smaxwell(--nospam--at)]
Sent: Monday, June 09, 2008 10:26 AM
To: seaint(--nospam--at)
Subject: RE: tornado alley


Keep in mind that the code is NOT intended to prevent EVERY natural event from destroying a house.  The code is meant as a life safety level for protections from is deemed by society as some "acceptable" level of effort.  In more technical terms, all the natural event loading covered by the codes have some assumed average return period.  For wind, if I recall properly, that is a 50 year return period.  That means that on average, every 50 years there should be a wind event that exceeds the code level wind event.  Thus, if you take your example of Oregon, if those are the only two events have happened in the past 50 or so years, then the code level of 90 mph seems to be right on target.


The point is that there is a difference between the code level intent and what I might deem to be a good idea.  Code is to protect life.  To me, the lack of straps in for the vast majority of the country still can achieve that goal.  And unless your uncle was in the shed at some point during that severe storm, straps were not needed for life safety on that shed.  Of course, there is NOTHING that says one cannot go beyond the code.  The reality is that no too many people want to go beyond the code and spend money on stuff that they don't see and don't understand (at least until they house is in ruins around them).  It is an unfortunately part of human nature.





Adrian, MI

-----Original Message-----
From: Andrew Kester, PE [mailto:akester(--nospam--at)]
Sent: Monday, June 09, 2008 11:07 AM
To: seaint(--nospam--at)
Subject: re: tornado alley

I agree with Scott, in that you cannot do much in terms of the higher level tornadoes. Head underground and pray to your god... However, there are close calls with tornadoes that produce high winds, as well as other weather phenomena like downbursts and mircrobursts, freak thunderstorms (my term), nor'easterlies, etc. that produce hurricane equivalent winds in non-hurricane regions of the country.


I was watching Axe Men, one of my new favorite shows, and they were covering that horrible storm that hit the Pacific NW last year. They had +90-100mph winds. They also talked about a storm in 1962 that was an "extratropical" cyclone Freda that hit Oregon and Washington and had sustained wind speeds up to 130mph!! Now I believe IBC has most or all of Oregon as 90mph. We can make all the codes we want, Nature does not play by our rule books!!



My point is I agree with the assertion straps and ABs should be standard everywhere. Such a tiny part of overall construction cost. Why people care so much about the flooring and cabinets of their house, and not about the structure is beyond me. They will gladly pay a realtor 6-7% but not 1% to the person responsible for the structural integrity of the house... Would you buy a fancy, gorgeous sports car with a crappy suspension, undersized engine, and lightweight easily crushed body just because it had leather seats and nice paint??


I was visiting my uncle in Oregon a couple of years ago, a Geotech/Civil Engineer. We went out to his mountain cabin where he had built a really niced 2x framed shed. I complained about no uplift straps and he started busting my Florida SE chops. So I talked him into going to Home Depot and I personally installed uplift straps myself to all of the rafters, top plate to studs, and studs to base plates.... He told me it did fine in that storm, maybe because of the straps, maybe because of the trees and mountain shielding. But for $50 and a couple of my hours I am sure I greatly increased the structural resistance of his shed...


Andrew Kester, P.E.
Principal/Project Manager
ADK Structural Engineering, PLLC
1510 E. Colonial Drive, Suite 301
Orlando, FL 32803