[TowerTalk] Which Vertical is More Robust ?

[Gedas]

Makes perfect sense Rick. It has been far too many decades since I had 
to take all our ME classes (like Mechanics of Materials) even though we 
were all EE's. You have told me exactly what I needed to know. TU again 
es HNY. 73

Gedas, W8BYA

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On 1/1/2020 1:59 PM, Richard (Rick) Karlquist wrote:
> For thin wall tubing of a given wall thickness
> and material, it is approximately true that strength
> is proportional to the square of the outer diameter,
> and stiffness is proportional to the cube of the outer diameter.
> Meanwhile, weight is approximately proportional to outer
> diameter, and wind force (for a given MPH) is proportional
> to outer diameter.
>
> Thus, doubling the diameter (all other things being equal)
> doubles the survivable wind force per square foot,
> which increases the MPH wind survival by the square root
> of 2 = 1.414, since wind force is proportional to the square of MPH.
>
> In terms of erection, larger diameter is an even bigger win.
> OTOH, the amount of sag for a given diameter is the same
> no matter what the wall thickness.  The increased weight
> exactly cancels out the increased stiffness.
>
> BTW, you don't need software to figure the above.  Any
> mechanical engineering handbook has all these facts.
>
> If you do use the fence rail, realize that the zinc
> plating is too thin to keep RF from impinging on the
> steel, a magnetic material.  Hard to say how lossy
> it is at RF, except that the DC resistivity is 6X that
> of copper.
>
> The fence rail is likely even stronger relative to EMT
> than would be predicted by the diameter.  EMT is specifically
> designed to be bendable.  Not what you want.  OTOH, fence
> rail, or course, is designed NOT to bend.
>
> I hope that all makes sense.
>
> Rick N6RK
>
>
> On 1/1/2020 9:54 AM, Gedas wrote:
>> Hi Rick es HNY !
>>
>> But let me ask my question again, is it better to go with a larger 
>> dia pipe (even if it has a greater wind load) or better to go with a 
>> smaller dia tubing with less wind load? Assuming the wall thickness 
>> is the same for all the members.
>>
>> Gedas, W8BYA
>>