List: 2 iitems in one post
90mph Wind Load:
Is this fastest mile? or 3-sec gust?
But I digress, National Building Codes have been around since the early 50's if
not before. There were 3 that were adopted by jurisdictions in the US, the UBC,
the SBC and BOCA. Actually there were a few more that were locally developed
but in general these were the codes. In the late 90's it was deemed a good idea
to put together these three and have one code for the US. It is called the IBC
(international building code, go figure) and it was first published in 2000 and
has been revised in 2003 and most recently 2006. These codes are
administratively adopted by individual jurisdictions, state, county, city as
the "life-safety" building code governing the design and construction of
structures in that jurisdiction. This has been the fact for over 60 years.
How does one get to the finding that it is a recent strategy by local
jurisdictions to regulate any specific users?
Back to the 90mph question; in the years since the 50's wind research and
design knowledge has increased many-fold and in an effort to provide
"life-safety" designs with efficient use of materials, the body of knowledge
concerning wind loading and wind effects has been evolving. The old codes
(UBC,SBC,BOCA), and I will talk UBC because I am still very familiar with that
old code, used a wind velocity (speed) measure as the "fastest mile" wind
velocity. The newer code (IBC) uses in its wind pressure determination a wind
velocity measure as 3-sec Gust. The old Vfm equates to a larger V3sec.
70mph(fm)=85mph(3sec); 75mph(fm)=90mph(3sec); 80 mph(fm)=100mph(3sec) and so on.
If the adopted code is IBC; then if the design wind is 90mph; then that is the
3-sec velocity, which would be 75mph in the older codes.
By the way, the TIA/EIA 222-F uses Vfm, the G revision uses V3sec.
This being said; I don't see any indication of some subversive activity by the
building officials. They are just asking that the structure be design based on
latest information utilizing the best available knowledge and techniques.
I have a vested interest in this.
I am a licensed civil engineer and licensed structural engineer in several
States and Canadian Provences. In every case the licensure laws have a
stipulation concerning stamping of work not done under the licensee's
responsible charge. This is wet stamping of drawings and calculations not
actually done under your direct supervision or hand. In order to stamp this
type of work the licensee must analyze the structure to sufficent detail to
assess that the design under question does indeed meet the required code
conditions. This is to be an independent proceedure from the original work. The
penalty for not following this prescription is forefiture of license.
Since my licenses are necessary for my livelyhood I would not place them in
As to the cost of this service, it depends on the complexity, detail, and
documentation required by the jurisdiction. I do this type of project for the
amateur community in the jurisdictions I am licensed in as a service at a
reduced rate, and they have run from $400 to $1500 in fee. I am not getting
wealthy with this type of work, I make many multiples of that with my
commercial client base and I have the same liability exposure.
Thanks for the soapbox and 73
Lonberg Design Group, Ltd.
H.S. Lonberg, P.E., S.E. / KR7X
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