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Pipe Deflection During Lifting 3

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Annette3

Annette3

Mechanical
Jul 26, 2007
2
Hello,

I was asked to figure out the amount of deflection in a pipe for two different lift contact points - with the majority of the load lift from the center and then with the load lifted from one end.

Originally I thought this would be a quick calculation where I could pull the equations off beam deflection tables, however when I did so the deflections I got were somewhat higher than I expected.

My parameters are: 50' length (yes, quite the long length!), 8" sched 40 steel pipe. It will either be lifted from one edge, or the middle (another strange thing, since I'm sure it would be too cumbersome to actually lift a 50' long pipe from only the middle).

From my understanding, the beam tables show either cantilevered beams or fixed-fixed beams. So is it possible to correlate these criteria to the fact that the beam is technically not fixed at any point?

Thanks!

Annette

 
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You should be lifting pipe with straps placed at both ends. The deflection will be wl^3/384EI, and yes it will be rather large.

<BTW I think lifting pipe from the middle or one end is an excellent way to get somebody hurt.>

 
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Lifting one end, the worst case has to be as it lifts and is supported only at the ends ... After that the higher the lift point gets, the smaller the deflection.

Assuming rho = 7850kg.m^3 and E = 192363 MPa ....

d = 5wl^4/(384EI) so d is approx 50mm at midspan

Lifted at the centre it's the same as two simple catilevers back to back since rotation at the centre will be zero.

d = wl^4/(8EI) and end deflections will be approx 30mm

Beware of local stresses particularly in the second case ... buckling may occur at the lift point.
 
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Biginch,

You got your post in whilst I was writing mine.
The equation you quoted is for a fixed end UDL beam, which this is not. Pinned ends would be more appropriate without moment restraint, so (5x) the deflection. Note that my 'w' is unit weight so l^4 is needed.
 
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Thanks C2it and BigInch!

C2it, I did the same thing as your first formula before and it did give me a more reasonable number. So I will stick with that! Thanks! :)
 
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You also want to consider inertia loads due to the lift.

This is realistic and will increase your deflection and stresses.

NozzleTwister
Houston, Texas
 
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For lifting from the center, assume pinned ends and superimpose a point load at the center (upwards) and a uniform load equal to the weight.

For lifting from the ends, assume pinned ends with uniform load. You'd also have some compression, which probably wouldn't drastically affect deflection in this case.

8" steel pipe doesn't normally suffer from local buckling, so it can have a fair bit of deflection and still be okay.
 
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Lifting from the centre: assume a cantilever fixed at the centre (or center if you are in the US)

 
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If you assumed pinned ends as I described, the end forces will cancel out, giving you "free" end conditions, which is what you'd need (and which is not normally tabulated in beam loading charts). The cantilever mentioned above would be simpler and give identical results, but I didn't think of it quick enough.
 
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