[TowerTalk] Stub mast strengthening

[Grant Saviers]

I managed to find the answer to a question that has bothered me re 
reinforcing with internal sleeves - do the ends of an internal sleeve 
need to be pinned to the outside sleeve to act as a single structural 
element?  Dave Leeson, W6NL in "Physical Design of Yagi Antennas" 
analyzed this and round tubes are a special case - they will act as a 
single member without pinning.  (page 4-20).  This is obviously not the 
case for sheet structures - it is easy to bend a paperback book or 
phonebook, even 1000 pages do not act as a single structure with one 
edge bound.

So this makes it easy to use internal sleeves to strengthen or increase 
the bending moment of tubular masts, Yagi elements or whatever.  
Internal sleeves just need enough fasteners or welding to stay in place.

Grant KZ1W


On 4/16/2013 11:49 AM, Chris wrote:
> Don't forget that strengthening the mast so it won't bend means that force is now presented elsewhere, i.e., on the tower itself.  Make sure the tower can handle it.
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> Chris
> KF7P
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> On Apr 16, 2013, at 12:44 PM, Grant Saviers wrote:
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>> Sleeving works, UST sells 20' x 2" x 1/8 wall steel masts with the lower 10' sleeved to 1/4".  With a 2.5" od (what is "thick wall" and what is the alloy and temper?) you potentially have a very strong mast.   What is the load?  Try one of the mast calculators before sleeving.  (ARRL, K7LXC)  or free by WD6P
>> http://www.math.niu.edu/KARC/mast/
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>> Grant KZ1W
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>> On 4/16/2013 8:31 AM, GW4BLE wrote:
>>> I have a question concerning 'sleeving' (can't think of a better way to describe it) -  I have a 16' x 2.5" OD thick-wall aluminium tube that will be used as a stub mast, would inserting 6' x 2" OD thick-wall aluminium  tube into the bottom of the tube add to its' 'strength' in any way or would it just add unnecessary weight?
>>> Sliding it in makes quite a snug fit, but not exactly 'tight'
>>>
>>> Steve
>>> GW4BLE
>>>
>>> Sent from my iPhone 4S
>>>
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