Disaster waiting to happen? Using PVC for deck supports???

[salty]

Yes, buckling that would be caused by the heat of a FIRE.

[Lou]

Check the temp that would cause steel to buckle. Now see what happens to concrete at that temp. Lou

[RicodJour]

In a wood framed building? I guess if the fire started at the base of the column that might be a good argument, but in any real situation the house would be engulfed in flames long before the plastic temperature of the steel was reached.

The concrete fill is to prevent buckling, partially from being dented, but also to prevent localized failure which can occur at lower loads than the straight compressive strength of the material(s) would indicate.

R

[Stormin Mormon]

When I was in college, so many years ago. We learned that cement is strong for compressive loads (such as columns in the cellar). Steel is good for stretching loads (hanging a bridge from a frame).

If your friend's use of concrete is to support weight, it may work very well. Concrete often has reinforcing bar, or rebar. This steel helps to combine the compression strength of concrete with the stretching strength of steel.

[Stormin Mormon]

Steel softens about 800F, if memory serves. Interior building fires can get over 1300F at ceiling level. Twenty year old information, I'm likely wrong. But the asbestos or cement around the steel helps in case of fire.

[PeterD]

Perhaps four years of engineering school? Or even two semesters of structural member strength?

[Glenn]

Cute. When you have 1300 degrees on the wood it's supporting, the column is the last thing I will be concerned with. In a total of some 45 years of construction, I have never seen this in my neck of the woods. Perhaps some are over educated?

[Thomas G. Marshall]

This makes sense to me, though I'm hardly as versed in structural analysis as the other denisins of this ng. Fire seems a concern, though secondary, only because the plasticity of steel could never be reached in a basement without the rest of the house already having been reduced to dust. Or so it seems to me. {shrug}

[mkirsch1]

Good thing the clown was dumb as a the post he broke his arm on because if he'd had a lick of smarts at all he would've sued you for the injuries he sustained trying to bash in your mailbox... and he would've won. You're lucky.

A friend of mine put boulders in his front yard because drunk drivers had missed the corner and ended up in his front yard on several occasions, and had hit both his house and his travel trailer at least once. The insurance company gave him 48 hours to have the boulders removed or they'd drop his policy. Long and short of it was, the boulders were a willful admission of wrongdoing/negligence in a lawsuit because they were put there to protect the house from drunk drivers. He could say they were decorative all he wanted, all they had to do in court was point out that the boulders were placed there AFTER the drunk hit his trailer, and he'd lose.

[Lou]

Well I'm no attorney but, that doesn't sound right. A drunk driver doesn't premeditate getting drunk and running into a house so therefore creates an accident. An idiot smashing mailboxes does premeditate the conditions, planning and carrying out the plan to destroy private property. He could have sued but my bet is that it would have backfired. Lou

[Matt Whiting]

It also adds tremendously to normal buckling resistance, not just buckling resistance due to fire reducing the capacity of the material.

[Matt Whiting]

No, buckling caused by heavy load as well. A column doesn't need fire to buckle.

Matt

[Matt Whiting]

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

[Edward Hennessey]

M:

Although no one addressed the question, the geophysical stability of the location would be of some measured consideration. Performance of the columns on soil subject to liquefaction in a seismic event merits concern in the right circumstances. A first-hand look at the density of steel used in the recent rebuilds of L.A. freeway overpass supports is amazing.

Whether the OP or owner has further interest in possible remedies for any shortcomings in this case is a another question.

Regards,

Edward Hennessey

[Pete C.]

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.

[Tom Cular]

Fire protection of structural steel is placed on the exterior of the members, not within a pipe or tube.

To make it simple, take a look at a typical pipe pile, driven empty, then filled with concrete, with a circular cage reinforcing only in the upper section (top 20-30'), a vertical bar or two near the center does nothing.

As Matt and Rico have stated the concrete fill is to resist buckling.

Tom

[Matt Whiting]

37,500 psi is a pressure, not a load. 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 the behavior of a short column is MUCH different than a long column. Ever heard of Euler?

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.

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.

Matt

[trader4]

And I would submit that it does a lot more than just provide the buckling resistance. Concrete is widely used to form structural support to hold up buildings, bridges, etc. Even in this deck example, what are the footers made of? They are essentially cylindrical concrete pillars. So, while the concrete does keep the steel pipes in a lolly column from buckling, which is clearly important, the concrete also carries some of the weight directly. If instead of concrete, you had some other means to keep the column from buckling, say an internal criss cross web of little rods, I would say the concrete filled lolly would carry substantially more weight.

[Pete C.]

It is both.

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.

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.

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.

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.

[CWatters]

PVC burns doesn't it?