[TowerTalk] Tower Wind Calcs

[Jim Lux]

At 02:43 PM 12/11/2003 -0800, Alan C. Zack wrote:
>I wonder if anyone would be kind enough to please point me in the
>right direction to find the method of obtaining a Wind CALC
>(calculation) for a tower project to satisfy my Building Department
>I am ready to purchase a U.S. Tower's MA-40/MAF-40/MAB-40 combination
>crank-up, fold over tubular tower.  I downloaded the Pier Footing
>(base) installation drawing for this tower from the U.S. Tower's web
>site and took it to my Henderson, NV, Building Department.  The
>Building Dept approved my tower and said the drawing was fine, EXCEPT,
>I needed a Nevada P.E. wet stamp on it (it has a CA PE stamp) and I
>also need a 90 MPH Wind CALC.

And a darn good thing, too... There's a reason why states require P.E.s 
licensed in that state... the rules are different in every state, and there 
is a certain amount of local knowledge involved in some areas (foundations, 
etc.)  For instance, I wouldn't necessarily expect a PE in South Dakota to 
know all about seismic loads and the geotechnical stuff peculiar to 
California. Likewise, I'd expect the So.Dak. P.E. to know all about ice and 
snow loads, whereas, I doubt the local folks over the counter in Thousand 
Oaks, CA, would care much about whether my tower would stand up to icing.


>First, I went to the ARRL web site looking for a ARRL volunteer P.E.
>but there are none shown for the state of Nevada.  Next, I contacted
>U.S. Towers and asked them for it.  I reasoned that since this is a
>considerable sale for them they would provide the wind calc at a
>nominal fee.  I was thinking this was something a computer generated
>program could spit out in a minute or so, or that there was some sort
>of table was available.

Yes and no... it's like the story about the plumber, the hammer, and the 
$1000 boiler repair.. The hammering costs a dollar, knowing where to hammer 
costs $999.


>  I was somewhat shocked when I was told the
>charge would be $250.00. When I asked why so high I was told no one
>on their staff could do it and they had to sublet it out to an outside
>P.E.

And, in the context of what most P.E.s do for a living, $250 IS a nominal 
fee.  That's probably 2-4 hours work, which, by the time the engineer works 
out the contract for the work with you (in California, you'd have to have a 
written contract in place before the engineering work can be done), 
understands what the pile of paper you've given him is, worked through the 
analysis and verified that it's correct, written his report, talked to you 
about it for a half hour or an hour, etc.. It all adds up.  Furthermore, 
you're probably running into a "minimum charge" issue here.  It's not cost 
effective for a professional to do lots of little $50 jobs. The "per job" 
overhead is significant (gotta run that office, pay for the lights, etc.).


>  I am surprised that they have engineers who design and test
>these towers but are unable to compute a 90 MPH wind calculation.

There's a big practical difference between designing and testing, and 
putting your signature and wet stamp on the drawing.  A failure on the 
former means you might get fired. A failure on the latter means you might 
go to jail.


>   The sales rep I spoke to was kind enough to email me the tower material,
>bolts, etc stress analysis and other specs along with the same drawing
>I had downloaded from the internet.  But the Building Dept still wants
>the 90 MPH wind CALCS.
>Is there someplace I can download the method of doing this.  I am
>hoping I may be able to do the calculation myself and find a P.E. who
>will recheck my figures and sign off on it for less than U.S. Towers
>wants to charge me.  I have an EE (1965) and a IE (manf) (1989) and
>think I would be able to do the numbers if shown how to do so.

Yep.. that would be a decent strategy.. Nevada is probably like most 
states, and has an online directory of licensed P.E.s with names, 
addresses, etc.  Search and find some candidates and call them up.  But, 
bear in mind the "minimum charge" phenomonon.

Analysis methodology is fairly straightforward, and covered in the TIA 
specs, at least partially, and you should be able to get that from the library.

>   I have
>even considered testing for my own NV PE stamp which may be cheaper
>than the $250.00 fee U.S. Tower wants but doubt if I could sign off my
>own project.

In California, at least, it would be cheaper to pay the $250.  The test 
alone is $175, and there's a significant amount of other stuff and time 
involved (if only because you apply some months before taking the test, and 
then wait some more months to hear if you passed).  If you're currently 
licensed in another state, you can apply for a license by comity, but I 
don't recall all the rules on that off-hand.  It's probably still as 
expensive, but it might be faster (if you don't have to take the test.. but 
then, every state potentially has different testing requirements).  License 
fees are a matter of revenue enhancement, as well.


>I would appreciate any help someone would be able to provide.  If it
>means finding a comparable tower from a different supplier who is more
>buyer friendly I am open to that also.
>TIA for any assistance.