[Towertalk] Antenna Wind Loading Calculations

[Frank C Travanty]

Dave,
Near as I can tell, the 70 MPH number for UST is the only one that has
the PE's name behind it, and thats for the antenna at one foot above the
tower top, with the tower at full height. I suspect it stops here because
it would be difficult to cover a large variety of antenna configurations
above the mast. If you have the UST Engineering specs, and antenna
loading you have the information needed to calculate the wind load at any
wind speed and tower height, with any antenna arrangement. I ran into the
same dilema a couple of years ago, and decided to write my own program
(in Excel) for the Tower bending Moment and the Mast loading for the
general case of up to six tower sections. The program is valid for self
supporting towers that have their worst case bending moment at the base.
You can find the spreadsheet on the ARRL QEX web site. Article was in
July/August 2001 QEX, or both can be found in the 2001 ARRL Periodicals.
Also, can do it manually by using the ARRL Antenna Book section on Towers
and windloading. This may not be adequate if you need a sign off from a
PE, but it should get you darn close before you need to spend any money.

73,
Frank W9JCC

On Sat, 22 Jun 2002 19:32:19 -0400 "David" <k4zzr@bellsouth.net> writes:
> I've run into the same question myself and am really surprised that 
> tower
> manufacturing companies don't give more structural info with their 
> products.
> For instance, US Towers gives windloads for 50mph and 70mph, and if 
> I need
> to know what the rating is at 105mph to meet building codes here in
> Florida - I have to hire an engineer.   I know that Florida isn't 
> the only
> state that requires >70mph documentation that building inspectors 
> need
> before issuing permits.   My hat is off to the tower manufacturers 
> who *do*
> list wind ratings of +100mph.   Why a tower manufacture would 
> require their
> customers to pay an engineer to rate their products is beyond me.   
> If a
> tower company sells towers to hams who live in states with >70mph 
> building
> codes, they should provide the necessary structural info required 
> by
> building departments.  Of course, that's just my opinion.  :-)
> 
> David, K4ZZR
> 
> ----- Original Message -----
> From: <BobK8IA@aol.com>
> To: <thoele@txcyber.com>; <towertalk@contesting.com>
> Sent: Saturday, June 22, 2002 5:30 PM
> Subject: Re: [Towertalk] Antenna Wind Loading Calculations
> 
> 
> > In a message dated 6/22/2002 3:52:16 PM Eastern Daylight Time,
> > thoele@txcyber.com writes:
> >
> >
> > > Howdy again -
> > >
> > > I found a couple of towers, but now I need to figure out how to
> calculate
> > > wind loading.  There seems to be so many variables, and Rohn's
> information
> > > seems very vague.
> > >
> > > Any help would be appreciated.
> > >
> > > Troy
> > >
> >
> > Hi Troy;
> >
> > If the towers can be identified as to mfr and model, the mfr can 
> certainly
> > supply you with the structural info you may need. If not, please 
> bite the
> > bullet and hire yourself a structural PE. Several hours of his/her 
> time is
> > worth every penny! Only then  can you be sure you will be loading 
> them
> > safely. Good luck.
> >
> >
> >
> > 73,Bob K8IA
> > Michigan USA
> >
> >
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> 
> 
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