[TowerTalk] FW: Mast Wall Thickness

[Joe Subich, W4TV]

 > Another way to express this is the increase in strength = 1 / the
 > percentage stress reduction.

Increasing the wall size does not "increase the strength" of the
material - it reduces the stress on the mast for a given load.
Put another way it increases the load handling capacity of the mast.

In any case, it is far better to increase the diameter of the mast -
the stress in a 2.5" OD 1/4" wall mast will be only about half that
in a 2" OD, 1/4" wall mast for the same applied load.  It's a shame
that the makers of antenna rotators simply don't understand that and
continue to insist on 2" mast only.

73,

    ... Joe, W4TV


On 2/26/2014 2:09 AM, Matt wrote:
> For a 2" OD tube mast with 1/8" wall thickness, increasing wall thickness
> will decrease stress for any given bending load as follows:
>
> 1/4" wall:  61% of 1/8" wall stress
> 3/8" wall:  49% of 1/8" wall stress
> 1/2" wall:  44% of 1/8" wall stress
> 2" solid rod: 41% of 1/8" watt stress
>
> Another way to express this is the increase in strength = 1 / the
> percentage stress reduction.
>
> Hope this helps.
>
> Matt
> KM5VI
>
>
>
>
>
>
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Jim
> Lux
> Sent: Tuesday, February 25, 2014 7:47 AM
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] Mast Wall Thickness
>
> On 2/24/14 9:39 AM, Chris Pinholster wrote:
>> I have been researching tower mast material. Both aluminum and steel.
>>
>> If aluminum 60601 tubing with 2"OD and .125 wall fails at 35000 ps,
>> what happens when you increase wall thickness?
>
> Not much it might seem, as it happens.  The outer part of the wall carries
> the peak stress and fails first (think about holding a bunch of spaghetti
> in your hand and bending it.. which strands break first?)
>
> This kind of thing goes as the 4th power of the radius.
>
> To the first order, you could estimate it as
>
> 1^4 - 0.875^4  =0.414 -> 1/8" wall
>
> 1^4 - 0.75^4   =0.684 -> 1/4" wall
>
> about 60% more strength for about twice as much metal.
>
>>
>> If you increase the thickness of the mast wall, wouldn't that increase
>> make a difference in the bend or failure rating? The charts at the
>> metal company I visited seemed to indicate that would be true.
>> (I was looking at aluminum 2"OD and 1.5"ID)
>>
>> Also I ran across a chart that showed that using a 14 ft mast, with 4
>> ft inside the tower and 10 ft above was stronger than an 11 ft mast
>> with only 1ft inside the tower and 10 ft above.
>>
>> Any opinion or science from this learned group?
>>
>>
>>
>> CHRIS PINHOLSTER k4win at mac.com
>>
>>
>>
>> _______________________________________________
>>
>>
>>
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