[Top] [All Lists]

Re: [TowerTalk] 2" OD pipe.. again

To: <>
Subject: Re: [TowerTalk] 2" OD pipe.. again
From: "Steve, W3AHL" <>
Reply-to: "Tower and HF antenna construction topics." <>
Date: Fri, 19 Mar 2010 20:52:43 -0400
List-post: <">>

Most of what you are asking is covered in a July/August 2001 QEX article by 
W9JCC and the accompanying spreadsheet:

Steve, W3AHL

Date: Fri, 19 Mar 2010 00:08:30 -0700
From: Kevin Normoyle <>
Subject: Re: [TowerTalk] 2" OD pipe.. again
To: "Tower and HF antenna construction topics."
Message-ID: <>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Question for the people who are sleeping at night:
If people create an antenna load that requires such a strong mast to 
resist bending, then that force is transferred to the top section of a 

How do people calculate the bending moment a top section can resist? 
It's difficult because most tower vendors spec a wind load close to the 
top of the tower right? And you don't know if the limit is because of a 
moment limit at the base, or a moment limit of the bottom of the top 
section. (unless you can analyze a lattice tower yourself).

If the moment limit is caused by the bottom of the top section 
(narrowest), then having 10' of mast past the top of the tower, can be 
be say a 50% increase in the moment the bottom of the top section has to 
deal with?

Or are people just worrying about cases with the tower cranked down. If 
so, isn't the wind going to be less then, since it's closer to the ground?

Is the real problem here ice loading? I'm wondering if people with 
anecdotal experience about mast failures are mostly in ice areas.

How do people calculate what a crankup tower, extended, can resist with 
10' of mast extending from the top, with ice loaded antennas?

If people are using spreadsheets, how come we don't have a spreadsheet 
that has "close enough" analysis for bending moments typical crankup 
tower sections can resist?

I have some big masts I've decided not to use, just because they're too 
damn heavy. Heavy on top is not a good thing. I've replaced rotor plates 
with 1/4" steel to boost vertical limits, but you hit the horizontal 
load limits of rotators etc.

Anyone have numbers/equations?


TowerTalk mailing list

<Prev in Thread] Current Thread [Next in Thread>