[TowerTalk] PIPE ANCHORS

[Randy]

I don't think you could find any competent engineer that would say "fill 
it with concrete to make it stronger", and be willing to sign off on 
it...he or she would specify something that wouldn't fail without doing 
that.  I do have it, from somebody I respect, that dropping PVC pipe 
inside of the top section of TV-type "push-up poles" will contribute 
towards keeping the thing from collapsing. I'd be interested to know 
that, if you could magically seal both ends of a tube, having already 
packed it with magic dry sand, whether it wouldn't increase the 
strength, as far as kinking in a bending moment goes. I'd guess that it 
would help, and if that's true, then concrete's compressive strength 
wouldn't matter, even if it fractured so badly that it turned to dust. 
Concrete is caustic; I don't know how that relates to steel, but as far 
as water pipes, it *will* eventually corroded a hole in it, X decades 
later. Maybe it's more complicated than mere pH.. I dunno.

73
Randy
KZ4RV

On 10/31/2011 10:34 PM, Jim Lux wrote:
> On 10/31/11 2:02 PM, Dorn Hetzel wrote:
>> But of course, filling the pipe or square tube with concrete probably
>> does help since bending would have to compress the concrete
>> fill and concrete *seriously* resists compression.  Especially if the
>> interior of the tube is rough enough for the concrete to bond
>> to it well (or some bolts are run through or such).
>>
>
> I'm not sure about that.  I looked through a bunch of references, and
> nobody seems to have measured the strength with/without concrete.
>
> Yes, concrete is strong in compression, but think about a pipe full of
> concrete and bending.  It stretches on the far side, and the concrete
> just cracks.  Concrete isn't very strong in bending.
>
> Overall, I don't think concrete fill buys you a lot, structurally,
> unless you're doing something like a prestressed concrete beam, so the
> side away from the load doesn't ever get into tension.
>
> Even in the compression side, the steel probably is stronger than the
> concrete in compression.  Concrete's big advantage is that it's cheap
> compared to steel.
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