Big, heavy mast

[sawyers]

(begin freebie plug)

I have just finished a paper about mast loading and mast strength for the 
Central States VHF/UHF meeting in Minneapolis around the end of July. I 
won't be able to present it due to a previous committment, but it will be 
in the Proceedings which you may be able to order. The Proceedings help pay 
for the meeting and I don't get a cent so please contact them. I did this 
as a service. I also get into rotor side load calculation and calculating 
the bending on a Rohn 25G hower that is house bracketed, so hopefully 
people will find it useful for preliminary analysis. 

(end of freebie plug)

While water pipe is not the preferred material for masts (it is soft) I 
know people are going to do it, so I included a table of allowed maximum 
bending moments based on an assumed 36,000 PSI yield bending stress. I am 
basing the assumed yield stress on a comparison of chemical composition of 
the ASTM standard for galvanized pipe and other similar steel compositions 
in the American Society for Metals Handbooks.

The governing equations for calculating have been published in several 
books and reviewed here in the last month.

Anyway the short answer to your question for 2 1/2" SCH 40 is 3192 ft.lbs. 
of bending load, assuming you know the pedigree on the steel meets ASTM 
standards. If you don't know, then use 27,000 psi and 3/4 of the 3192, or 
2400 ft.lbs.

BTW a 1 1/2" SCH 40 mast (1.900" OD) comes out with 979 ft.lbs. assuming 
36,000PSI yield, or 734 ft.lbs if you go with 27,000 PSI yield strength. So 
in this case bigger is better.

I don't know your location or tower height or anticipated antennas so can't 
make any other comments, other than to make sure you put a drain hole in 
the bottom of the mast when you put in the insert, and probably a cap on 
top to keep birdy do-do from plugging the drain hole. (Actually saw a 
freeze break in a tower leg because of that stuff!)

Good luck, and have a local engineer check out your material and 
installation details.

de n0yvy Steven H. Sawyers PE - ARRL Volunteer Consulting Engineer

disclaimer: I and my company agree on at least one thing: My opinions are 
my own.


______________________________ Reply Separator _________________________________
Subject: Big, heavy mast
Author:  K7LXC@aol.com at ccmgw1
Date:    6/19/96 12:07 AM


In a message dated 96-06-18 21:08:57 EDT, you write:

<< Forwarded Message:
Subj: Big, heavy mast
Date: 96-06-18 11:19:13 EDT
From: sbookout@mail1.mnsinc.com (Steve Bookout) 
To: k7lxc@contesting.com

Hi Steve. 
Could you please send this out over the tower reflector.  My mail handler 
can not, for some reason, cope with the reflectors.  Keeps sending them back 
to me as undeliverable.  I would appreciate it.  73 Steve, NJ4F

               *************************************************************
*************

Howdy all.

How strong is strong? 

I have had a 2 1/2" schedule 80, 21 foot long piece of pipe stored for years 
hoping someday to use it for a mast.  I measures just under 3" OD and weighs 
166 lbs.  Just standard schedule 80 galvanized pipe.  A real beast.  I 
figured on machining down a piece of stock to fit in the end and to fit in 
the tailtwister.  Figured I would pin it in place to hold it all together. 
That is, pin it in the pipe not the rotator.  I have a pair of the tb-4's 
and planned on using both in this application like I do the tb-3 with 
smaller stuff.  Makes it real handy when working on rotator.  I usually keep 
about 6-7 feet of the mast in the tower. 
 Although I have hefted long masts over the top of a tower in the past, I
think I  will "build" this one into the tower from the beginning. Put two 
sections together with the pipe inside and do the 'ol Iwo Jima trick. 
Unless, of course, there is a better way to get it done with the Rohn 45.

For clarity, I'm really not a blivet when it comes to this stuff. I hve a 
ton of practical applications experience with this kind of stuff and tend to 
be conservative in my approach to things.  I just thougt this would be a 
good follow-on to the thread that is currently being 'spun'.

Any comments on suitability as a mast, loading, installing, etc.

73, Steve, NJ4F
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