Fill tall pole with concrete - cure?

[Matt Whiting]

The rebar on the pipe centerline was just wasted metal.

Matt

[Nehmo Sergheyev]

They are not "completely different concepts"; they are related concepts, particularly with the issue at hand. Now, what I said was this:

"A pipe filled with concrete, a 3" pipe for this example, is much stronger (and stiffer, if that's the term we want to use)."

*I* specifically differentiated between the two terms, and I parenthetically offered the term "stiffer" because that's the one he used. I used "stronger" because that's easier to understand and I believe that's what he meant anyway. But either term doesn't work. A concrete-filled steel pipe is stronger and stiffer than one that is empty.

It's absurd to argue otherwise.

I'm beginning to conclude you two have never been out in the field. I've got a pipe filled with concrete two blocks from here. It's stronger AND stiffer than the same pipe would be if it were empty.

Let's say it is used as a beam supported at both ends. A given amount of weight in the center will make it deflect less than that same weight on an empty pipe. Do you think otherwise?

The difference is so much, if I didn't know you both were humorless, I would think you were joking.

++++++++++++++

"Concrete-Filled Steel Tube (CFT) Structural System is a completely new system based on filling steel tubes with high-strength concrete. The CFT Structural System promises excellent structural characteristics; including rigidity, strength, deformation capacity," Steel Pole Goes Up in Southern Florida of the main advantages is the interaction between the steel tube and concrete: local buckling of the steel tube is delayed by the restraint of the concrete, and the strength of concrete is increased by the confining effect of the steel tube. There's more in this search: ,

-- (||) Nehmo (||)

----------------------------------------

[Tom Cular]

Snip:

The concrete fill of a thin wall tube, i.e.: a pipe pile or lally column increases resistance to buckling in compression and bending failure in the case of piles exposed to lateral loads, other than that, it just adds mass.

Tom

[Matt Whiting]

No, they are completely different. Stiffness is related to the slope of the stress/strain relationship (elastic modulus) in its linear range. Strength is how high the curve goes before failure. Not the same at all. A material can be very stiff (glass), yet not strong (glass with a small surface crack). A material can be very strong (spring steel), yet not very stiff (spring steel).

Let's say you support the empty pipe as you say above (as a simply supported beam) and measure its deflection in the center. Now stand the pipe up, fill it with concrete and let it cure and then support it the same way again and measure the deflection in the center. Which case do you think will have greater deflection? And now explain why your stiffer pipe has more deflection than the less stiff pipe that has no concrete.

Matt

[Matt Whiting]

And it really only helps in bending failure when buckling is the failure mode.

Matt

[Mike Hammer]

I WAS having problems with the pole regarding buckling and bending failure until I gave it some Viagra. Now it is stiff, straight, and hard.

Hey! Who painted the smiley face on the backboard? (-;

[Glenn]

Ahhh, that explains a lot. Book learnt but no experience. For your information, a hole in the ground is where you can pour a foundation, your butt is just above your legs. You will have to know the difference when you get out into the real world.

[Nehmo Sergheyev]

I'll go along with that experiment. But you can't make the conclusions, let alone explain them, before you conduct the experiment.

The pipe is a beam, 8 feet from support to support. The exterior diameter is 3 inches. The wall thickness is the same in both. We'll use schedule 40 because that's the example I think I can get.

One pipe is empty and is referred to as "empty"; the other pipe is filled with cured concrete and is called "filled".

The deflection in either case is hard to measure when we are only using the weight of the pipe itself to cause the deflection. However, I can stand on the center of the pipe. I weigh 211 pounds. (If the experiment is conducted without me, someone else can substitute.)

In the filled pipe, there will be small deflection. It would even be hard to measure with regular rulers.

In the empty pipe, there will be considerable, easily noticeable and measurable deflection.

There will be more deflection in the empty pipe than in the filled pipe.

You disagree with my last 3 paragraphs. Correct? Now, all we have to do is find an acceptable way to do this experiment. We need someone impartial to judge, and perhaps you want to put some money on this?

Well, I don't want to be rude. If you don't want to bet, that's okay. But the loser should have to do something.

-- (||) Nehmo (||)

[Michael Bulatovich]

That was rude, and unnecessary.

[Nehmo Sergheyev]

It's not something I would have wrote, but it's not that horrible. If that's the level you plonk at, you're going to be doing a lot of plonking. Glenn didn't name call, threaten, or even swear. Indeed, he was trying to avoid directly saying Matt doesn't know his ass from a hole in the ground.

And if you'll notice, Matt, in different ways, is rude a lot himself. For example, he's paraphrasing me incorrectly in this very thread. He's pretending there's some third party reading his post by itself. I suppose If they were to do that, they might be inclined to side with him. It's vary irritating, and he knows it. When you respond to Matt, the first thing you have to do, time and time again, is attempt to correct what he claims you said.

Now, that's enough of that. The issue is simply whether a concrete- filled steel pipe is stiffer than one that is empty. I say it is. Matt and Bob, amazingly, disagree with me.

Glenn was trying to explain how Matt could possibly be thinking this way. I've been wondering myself. Anybody who's had any real-world experience with a concrete-filled tube knows it's stiff. Thus, Matt must not have any experience of this nature.

-- (||) Nehmo (||)

[Matt Whiting]

The scenario is the self-weight only, no applied load.

Matt

[Matt Whiting]

From the mouths of babes...

[Matt Whiting]

Michael, don't sweat it. People of his IQ say dumb things all the time.

Matt

[Michael Bulatovich]

I can and I do, as you say. Newsgroups are like the first hockey tryout with

50 skaters on the ice. You don't (can't) pick out the good ones, it takes too much time. The cuts are quicker and easier to see and make. When the crowd is gone you can focus on qualities of individuals.

[Matt Whiting]

Show one place where I paraphrased you incorrectly. Just one example.

Let me see ... Bob is a PE and SE with many years of experience. I'm a PE and nearly complete with a graduate degree in SE (need to complete the final capstone project). And your credentials are???

Amazing that you can make this claim when you don't even know the difference between strength and stiffness.

Matt

[Michael Bulatovich]

Plonking requires no sweat, and this is not a question about IQ. It's about EQ.

[Matt Whiting]

:-), yes, very true!

[Nehmo Sergheyev]

Why would you be afraid of a little weight? Weight is the force that is going to make the pipe deflect. Besides, as I said, the deflection of filled pipe is going to be hard to measure if we only use the weight of the beam. We have to measure relative stiffness, you know.

-- (||) Nehmo (||)

[Nehmo Sergheyev]

The phrase, "pearls of wisdom can come from the mouths of babes, fools, and drunks", which is often used elliptically as you did, means that something said my someone uncorrupted or uninhibited is true. Thus, in the context you used it, you are saying what Glenn said is true. In other words, you are agreeing you don't know your ass from a hole in the ground.

-- (||) Nehmo (||)

[Bill]

The results are in!

I filled my 10 ft. high 3 inch schedule 80 pipe with concrete (3 ft. is underground, total pipe length 13 ft.).

Scientific results:

Before filled with concrete: I would tap on the top of the pipe with my hand and the pipe would "wiggle". And it would continue to "wiggle" back and forth for 10 seconds or more.

After filled with concrete: I tap on the top of the pipe with my hand and the pipe "moves" just a little and stops moving after about a second.

So this is very good for my motorized 12 ft. wire mesh satellite dish antenna. These things point at satellites 25,000 miles up in the sky. Needless to say, they need to be aimed extremely accurately. 1/8 inch in aiming can make the difference in being able to lock in a satellite or not (with some of the weaker satellites). And prior to concrete filling, I would guess the pipe was wiggling 1/2 inch to 3/4 inch back and forth.

So having the wind blow on the dish and making it "wiggle" constantly would not be a good thing.

As to the size of the pipe, my dish has a mounting collar for this size pipe.

I left a 10 ft. length of 1/2" rebar in the concrete in the pole. I basically used this along with hammering the side of the pole to get the concrete to "settle" while pouring. I would slide the rebar up and down inside the pole. And hammer on the sides of the pole with a hammer.

Then I just left the rebar inside the pole when I was done with this. I don't think there is any need for the rebar in the concrete??? But I would have had no other use for it, so might as well leave it in the pole...

Anyway "wiggle" problem solved.

And I love the internet! Ask a question and get all sorts of technical discussion. Another interesting thing for you engineering types would be a "tuned mass damper" for my satellite pole! Info on tuned mass dampers...