[TowerTalk] MASTS

[Jim Thomson]

Date: Tue, 15 Mar 2016 21:03:45 -0500
From: "Jeff AC0C" <keepwalking188 at ac0c.com>
To: <TexasRF at aol.com>, <towertalk at contesting.com>, "Grant Saviers"
<grants2 at pacbell.net>
Subject: Re: [TowerTalk] [Bulk] Re:  MASTS

What is possible in the worst case and what is likely seem two different 
things.  I've not seen EMT do anything other than just bend (which it does 
pretty easily) and buckle (if you really really abuse it).

So while I can imagine a scenario where the beam is bent back and forth by 
alternativing massive blasts of wind resulting in a buckle being introduced 
on both sides of the mast - eventually causing it to break and the thing 
flying off, that seems pretty bizarre.  The more likely case is that it will 
just bend - and a guy will look out his window and wonder why his beam has a 
big tilt that was not there before last night's storm.

73/jeff/ac0c

##  Rigid  EMT, whether  steel or  AL, is designed to be bent, in a bender ! 
The smaller diameter  EMT is bent using a hand bender, which is just a
3-4 ft long steel tube  with a radius arc  trough welded to the end of it.

##  On the bigger  OD  EMT tubing,  like the  2-3-4-5 inch OD  stuff,  we used 
hydraulic benders.   Even the bigger  OD  EMT is  thin wall material.   Its  thin,
so its  easily bent into a 45 to 90 deg angle. 

##  I would  not be using   EMT for  either a mast nor a gin pole.   Its  paper
thin wall, and low ksi  to begin with.   Galvanized  sched  40 or sched  80
35 ksi water pipe is a helluva lot  stronger...and heavier.   

##  You can ‘test’  the pipe  by strapping it to your deck, with a mile of it
hanging off the deck, then  applying  more and more weight to the far end.

##  UST uses  sched  80, 46-48 ksi pipe  for their tower legs.   However,
on mine, they also inserted a 7 ft, 2 inch long machined piece of steel  tube into
the bottom of each section leg, to increase wall thickness. 

##  Use the correct material for the job, whether  gin pole or mast.   If the yagi is 
only  within 3 ft of the top of the tower,  you can use almost anything.   The mast calculator
will tell you at a glance, if you have it correct. 

##  Local tower  installer uses a 2.375 OD,  sched  80  Al   pipe, for his gin pole, its 
20 ft long.   Aprx .202 thick. 

Jim   VE7RF