At 12:29 PM 3/3/2006, VAN FAIR wrote:
>I am currently using 3"OD steel pipe for my above ground guys for a Rohn
>25 tower. The post are 9 feet with 5 feet above hard ground set in
>concrete. I want to fill the post with concrete and one long rebar to
>strengthen them against bending. Would concrete with gravel or just cement
>with sand be better inside the pipes? I do not live in a high wind area.
>Thanks for your help. Van
Rebar does almost nothing for bending stiffness (it bends pretty easily).
I'd hate to try and figure out what effect a 2" column of concrete inside a
tube might have on the strength and/or stiffness. Certainly isn't going to
make it a heck of a lot stronger, in a outright failure sense.
That's a pretty skinny pipe, with a lot of load concentrated at the point
where it leaves the ground, so it's gonna bend without much load. It
probably won't actually fail in tension, but bend over, almost
certainly. (60 inch lever arm, 3" base, 240:1 mechanical advantage.. 100
lbs at the end of the pipe is 24000 pounds at the wall of the pipe at the
In fact, stiffening it with concrete might make the entire system weaker,
because it might reduce some of the "springy" ness of the original (empty
pipe) scheme, so more of the load is concentrated at the ground level. it
might also make it stronger... hard to tell.
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