Matt Whiting wrote:

Pete C. wrote:
Matt Whiting wrote:
Pete C. wrote:
Matt Whiting wrote:
Pete C. wrote:
"Thomas G. Marshall" wrote:
There was a person I was speaking to recently who was proud of what he
considered to be a very bright move on his part.

He had noticed that the lolly-columns in his basement had been filled with
cement prior to being used. He assumed that the strength of the support was
in the cement, and therefore concluded it was a good idea to try filling PVC
tubes and using those as posts (note-not as sonno-tubes, but as fully
structural support posts).

I pointed out that I thought that the strength of a lolly was in the steel,
and that the cement was there merely to ensure that it was never dented,
causing it to fold like an aluminum can. I was concerned that the first
major frost heave under his deck that is able to stress the ledger enough to
pull outward a small amount would cause his pvc+cement "posts" to break.

Was I right?
There are code approved PVC pipe based deck support columns available.
The compressive strength of PVC pipe is tremendous as long as you keep
it from buckling. I once tested a 1' length of 4" sch40 PVC pipe in a
hydraulic press and it too over 30 tons of force before it started to
fail (Enerpac press with pressure gauge). The compressive strength of
concrete is also very high. Combined strength is more than adequate and
PVC handles cold pretty well also.
I'd hardly call it tremendous. 8300 psi exceed most standard concrete,
although high strength concrete is available now that substantially
exceeds this value. And this falls FAR short of even standard A36 steel.

http://www.harvel.com/piping-clear-pvc.asp
8300 psi? I come up with more like 37,500 psi since this was 4" dia sch
40 PVC pipe with no filling i.e. 60,000# load on something like 1.6
square inches of PVC total.
Material properties don't depend on the size of the pipe. Did you even
open the reference I provided? Do you understand MATERIAL properties?

Matt

Do you understand that under testing in my 50T press, it took a load of
~37,500 PSI on the 1' length of 4" sch 40 PVC pipe before it failed?
Material properties are irrelevant, that was the actual result of the
test I noted.

37,500 psi is a pressure, not a load.

It is both.

Material properties are not only
relevant, they are essential to almost all structural engineering
calculations (I know as I have a masters in civil/structural).

And what I presented was not a structural engineering calculation it was
simply the results of a real world test that point out that sch 40 PVC
pipe is a lot stronger than most people think.

And the
behavior of a short column is MUCH different than a long column. Ever
heard of Euler?

No kidding, and again, I didn't present any structural engineering info,
simply actual results of a real world test showing the surprising
strength of PVC pipe.


A nearly pure compression test (which is what a 1' long 4" pipe
comprises) has almost no relevance to the case of a column that has a
substantially different slenderness ratio and thus subject to a buckling
failure mode as well as possible bending moments due to eccentric loading.

Right, but again, I didn't present anything to the contrary. I indicated
that code approved PVC pipe based deck supports were available, which
they are, and an example showing that PVC pipe is stronger than people
think.


I didn't see a column length in the OP, but when "basement" is the
description rather than "crawl space" it is likely that the length is at
least 6' and possibly 8' or even more. This is far from being a 1'
column. Concrete filled PVC could work if sized properly, but using the
same size as the existing steel column is a fool's errand. Again, the
OP didn't mention the size of either the steel or the PVC, but I'll bet
there were likely nearly the same size. If that is the case, then the
PVC is almost certainly inadequate, unless the steel column was grossly
oversized for the required load.

Probably, and I didn't suggest the OP's scenario was proper or safe. I
simply noted that "Using PVC for deck supports" as in the subject line
is possible and code approved if done properly, and not a "Disaster
waiting to happen" as was also in the subject line. Can't seem to find a
link to the product at the moment. Believe I read about it in Fine
Homebuilding or perhaps JLC.