On Mon, 2011-10-31 at 19:34 -0700, 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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