[TowerTalk] Square tubing

[Jim Thomson]

Date: Fri, 4 Aug 2017 10:27:54 -0400
From: Charles Morrison <junkcmp at gmail.com>
To: towertalk at contesting.com
Subject: [TowerTalk] Square tubing

<What changes or corrections are needed to Jim Lesson's formulas to
<calculate survival of square tubing booms ?

<-Charlie N1RR

##  good question. leeson used the old EIA-RS 222-C  spec.  A  4 inch OD
boom has a 12.56 inch circumference..and a  4 x .67 =  2.67 inch effective surface area.  

## A  3 inch square boom has a 12 inch circumference..and a 3 inch effective surface area. 

##  In both cases the  circumference is aprx the same...the 4 inch boom is slightly more... by 5%. 
The windload on the  3 in square boom will be more...by 12.4%....   3 / 2.67 = 5% more. 
The 3 inch square boom could be viewed as a pair of 3 inch x 1.5 inch channels back to back. 
Anybody who has used channel aluminum will attest that its stupid strong stuff.  
And with 2 of em to form a square tube, its really strong. 

## Drive over a piece of the  4 inch OD tube  vs the  3 inch square  tubing to see the effect..with both having the
same wall thickness....and yield strength.  Square remains intact.  The round gets crushed. 

##  I have the notes on square vs round for windload data..buried on the lap top.  I will see if I can dig em up. 
Lb for lb, the square tubing is stronger..and typ used for extreme windload applications for booms..provided
you can obtain square tubing that will slip fit and telescope into the next size up or down, to make a splice..and
also the same yield strength as round tubing.  Optibeam will use both square + round booms on their yagis. 

Jim   VE7RF.