Stregth of pipe

screwbean

Hello the forum;
I am brand new here so I beg you indulgence.
How do I calculate the amout of weight a pipe will support if used in a cantilever cituation?

FredGarvin

You would calculate it the same way you would do any cantilever beam calculation. The shape will dictate the area moment of inertia.

You will need to define what you consider for failure criteria.

screwbean

Thank you Fred;
What I am trying to ditermine is will a certain size pipe be strong enough for a crane if the pipe is inserted into a hole in the slab and ground. I would dig a 12" hole 4' deep and use a pipe of 8 5/8" diameter with 1/2" wall thickness. The pipe is made of 60,000 psi material.
The pipe would extend above the floor 5'. The crane would be attached to the top of the pipe and act as a lever arm of 3' in length @90 degrees to the pipe, the load on the crane would be 3200#.

I don't want to pipe to deflect past it' elasticity point.
Please help
Thanks

Q_Goest

Hi screwbean. From your post, this doesn't sound like homework, so I'll just give you the answer. Yes.

ok, just kidding. Why a 12" hole for an 8" pipe? bearings? This is a jib crane, right?

A 3500 pound load hanging off a horizontal arm (perpendicular to your 8", verticle pipe) and positioned 36" from the pipe centerline gives you a moment of 36x3500 = 126,000 inch pounds. This will produce a stress in the pipe of 5,140 psi. There's an additional axial load which I'll neglect because it isn't much. Deflection is around 0.072". I think you can also neglect column buckling in this case, just not enough load.

If I've interpreted your crane correctly, then you're well within design limits. But what's with that big hole your shoving this in? (I hate giving advice on the net when there's very little description or explanation of what this is used for. Kinda hard to ensure nothing's being overlooked.)

Oh - couple more things. Do a proof load on it just to make sure. If the maximum working load is 3500 pounds, put 1.5 times that much on it and make sure it doesn't break.

And if this is a commercial application, just forget everything and get a proper crane manufacturer to sell you one. You don't want to take the liability if it's going to be used by employees.

FredGarvin

Gotcha. Q beat me to the post so I'll just say that from experience and gut feel (not to mention the numbers Q posted) that you'll be fine. I assumed you'll cut such a large hole because you're going to back fill with cement.

You're buckling load is very high so definitely no need to worry there.

Along the lines also of what Q mentioned, we have a lot of hoists and cranes in our facility. We assemble many of them. However, we get an outside company to come in and certify them. If this is for a commercial application, it would be definitely worth the money to do so as well.