[TowerTalk] Stub mast strengthening

[n8de at thepoint.net]

After reading the original post and all the replies, I'm still  
wondering WHERE the 'junction' of the internal 'strengthening' and the  
out mast will be in relation to the tower top/bearing.

If there is to be some huge antennna at the top end of this mast, NO  
internal strengthening will decrease the 'failure mode' for the mast  
at the tower top IF the point I mentioned above is INSIDE the tower.

If it is NOT inside the tower ... that point will be the 'failure'  
point for the system when a huge wind strikes the top antenna.

Hope I made myself clear.

73
Don
N8DE


Quoting K8RI <K8RI-on-TowerTalk at tm.net>:

> On 4/16/2013 9:04 AM, Bob K6UJ wrote:
>> Steve,
>>
>> The sleeve would definitely add strength.  The lateral force from   
>> the wind load on an antenna mounted on the mast puts the most stress
>> at the bottom of the mast, think of a 16 foot lever arm.   I would   
>> find out the yield strength of your aluminum mast and do a
>> check of the maximum antenna load you should use.  Aluminum has a   
>> much lower yield strength than a steel mast so you need to be   
>> careful.
>> There are calculator programs available to help you figure out the   
>> load rating of various mast materials.
>
> There are many alloys of widely varying strength from both a
> flexibility ans yield strength.  The most common, 6061T6 is neither the
> strongest, nor cheapest.
>
> I use a lot of the 6061T6, but not in antennas. A 2" diameter piece
> with 0.25" wall, 24' long is heavy and when used as a gin pole displays
> a surprising amount of flexibility.
>
> 73
>
> Roger
>>
>>
>> Bob
>> K6UJ
>>
>> On Apr 16, 2013, at 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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