I don't think so. When you get that 12' wire mesh dish installed that pipe will sway all over the place in the slightest breeze. You'll be able to move it with a touch of your finger. I thought you were using steel pipe. I'm sorry to say but you've wasted your time.
As expected by those of us with technical backgrounds. You have changed the mass of the pole and thus have changed its natural frequency of vibration. You have not changed the strength of the pole appreciably, but have substantially changed the force it takes to get it vibrate. Those are not the same thing.
Wow, I didn't read every word but the use of concrete/steel composite structural elements (usually as a pile or a column) has been pretty well documented for decades. Concrete filled pipe or tube is substantially stronger than when empty, you don't have to guess at it the research has been ongoing for quite some time. I'd guess that anyone with an internet connection and a few minutes could dredge up some numbers, if not, they could definitly find WHERE to get those numbers. I would give a couple of references, but that would be too easy. Structural engineers should know these things in my opinion.
JTMcC.
The whole subject has gotten out of hand. Concrete filled pipes can be a good idea when used in the proper location. But, there is a world of difference between a large diameter concrete filled pipe pile and a small diameter pipe post. Many posts under this subject have confused strength with stiffness, and strength with resistance to vibration. It is the resistance to vibration that was the subject of the original post. Filling a pipe with concrete will change the mass and will change the natural period of vibration. Buying a thicker walled pipe will do the same thing and be a lot easier that trying to pour concrete down a 3-inch pipe.
Some posters on this subject have said things like, "If I bang on a concrete pipe filled with concrete it won't dent, and thus must be stronger." Sure, it won't dent. But the bending stiffness when acting as a cantilever column of a small diameter pipe is not appreciably changed by the addition of the concrete. It will still vibrate, just not with as much magnitude because it takes a higher force to move the larger mass the same distance.
My point all along has been that in this instance buying a larger diameter or thicker walled pipe is more cost effective than trying to fill a small diameter pipe with concrete, I.e., if you value your time. Maybe for some it is a wonderful Zen exercise to put concrete in a small hole and tamp it down to the bottom. That's okay by me. Just don't expect miracles.
Generally, a steel pipe filled with concrete will have almost twice the bending strength as the same pipe with no concrete. If that is not enough increase in strength for your purposes then you must go with a larger pipe. Of course that pipe can then be filled with concrete to double ITS strength. Filling a pipe with concrete will always increase its strength but you have to match the pipe size to the application.
Yes, as I mentioned some time back, adding that much mass will make a lot of different in the vibration characteristics.
Matt
Yes, and the latter has the advantage of dramatically increasing stiffness and strength as well as changing the natural frequency.
Matt
Out of hand???? Interweb police have maybe shown up? From your posts here I have to think that you have no experience with concrete filled columns or piling, of any diameter, or you wouldn't of posted some of the comments you've made. The gains to be made by filling a tube or pipe are out there for most to view, including you. I'm not a SE but I have them on the payroll from time to time, and we deal with concrete (or grout) filled tubes and pipes from time to time and you are disregarding a substantial gain that this guy can attain with little time/money/effort. Do everyone a favor and do the research, I certainly have, and quit trying to defend a somewhat indefensible position.
JTMcC.
If you have done the research, post one source here that shows the stiffness gain from filling a tall, skinny pipe with concrete.
Matt
MY SENTIMENTS EXACTLY!
(and yes I meant to shout!)
Once again you have missed my point. Filling large diameter pipes can have some beneficial effects for the cost involved. The work required to fill a small diameter pipe (we are talking 3" diameter here) does not provide sufficient beneficial effect to warrant the extra work required.
And yes I have often dealt with large diameter pipe piles and have chosen not to fill them with concrete because the minor gain in stiffness did not warrant the extra cost. If your SE's are recommending concrete filled tubes then I suggest you have them demonstrate the cost benefits of doing so as compared to simply using a larger diameter or thicker wall.
Many of you seem to think I'm an idiot. That's okay. I know what I know and anything you may say can't change the physics. So, if you have a real argument that can be backed by real numbers then let me see it.
I will even propose a problem to be solved:
A 3-inch x 0.120" wall pipe. Pipe is 3" OD. Install a 24-inch diameter dish antenna at the top of 12 feet of pole. Apply a 10 psf wind load to the dish (you may ignore the wind pressure on the pole). Compute the deflection at the top of the pole with the pipe empty and with the pipe filled with concrete. Now increase the wall thickness to 0.250" and compute the deflection at the top of the pole. Tell me which pole deflects the least. For simplicity you may assume that the pole is fixed at the ground line (not really true, but for this exercise we will assume it to be so.)
Localized buckling of the pole need not be considered for this exercise although with a 0.120" wall and 12 feet of height this is certainly a consideration for the unfilled condition.
I have quite a bit to get done this week, I certainly don't have the time you do to spend chatting on usenet. So I don't intend to do your homework for you.
I'll leave these thoughts as my last comment on your little arguement.
I'm guessing those recomending heavy wall pipe as a solution have not tried buying pipe in todays marketplace, and probably haven't priced or checked availability, and certainly not in the incredibly small length this guy needs for his dish.
JTMcC
You're talking economics here.
Do a Google search and you will see that this is being done in bridge and other construction because it is CHEAPER. Concrete is cheaper than steel. If you chose not to increase the strength of your pilings then that was an economical decision - not a structural decision.
If many think you're an idiot then perhaps YOU should come up with the real numbers. You can do a simple Google search and discover that pipe filled with concrete nearly doubles its strength. The argument about the diameter or length of the pipe is ludicrous. Adding concrete only doubles the strength - it is not a substitute for using the correct diameter/length of pipe for the application.
Mike:
You are mixing apples and oranges. Filling large diameter pipes used in bridges and other construction is different than filling small diameter pipes used for a TV dish. On a large scale project with large diameter pipe, filling them with concrete can make sense depending on the application. However, all too often it is being done simply because, "We've always done it that way." And, not because someone has actually studies whether or not it makes economic and engineering sense to do so.
Try working the problem I posed. You will find that an unfilled 3-inch OD pipe with 0.25" wall is stiffer than a 3-inch OD pipe, 0.120" wall filled with concrete. It's that simple.
OK. If that is all you were trying to say then I agree with you. I was thinking that someone said that adding concrete does not increase the stiffness/strength of a pipe. It may not increase it enough for a particular application but it does increase it.
Exactly! That's all I've been trying to say.
You were?? Could have fooled me.
Isn't it time we shook hands and moved on? [g]
Okay by me.
I promise not to post any more on this subject.
The work required to
It probably does for this homeowner.
The poor guy only needed 10' of pipe. The price difference (for a walk in customer) between 3" sch 40 and 3" sch 80 is going to be right around $5.50/foot. So just in material cost he's saved aprox. $55. using sch 40. A couple of bags of concrete or what ever type of mix he used isn't going to be over 7 or 8 bucks.
You have to take into account that there aren't a lot places willing to cut off a 10' piece of pipe for a homeowner. They are out there, but you may have to drive a bit farthur and they will charge you for the cut and likely charge you more on the pipe for buying such a small quantity. It would be similar to going to the lumber yard and asking them to cut 3' off a 8' 2X4, they might do it but they might not.
And if you live in a small town the sch 80 will probably have to be ordered. Try special ordering 10' of pipe. And for the last several years the pipe mills have been working at a pace that means there are times thru the year when a size of pipe is sold out and you have to wait for them to roll that size again.
So I can easily see why a guy would spend the morning in his back yard with a garden hose and a wheelbarrow filling the pipe with (fill in the blank). It makes quite a bit of sense.
And the use of composite columns in small diameter, slender applications is just as well documented as it is in big bore cans.
JTMcC.
I wouldn't recommend a trip to Vegas as your bluffing technique needs some work.
Matt
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