Lightly Loaded Jib Crane Deflection

Structural Engineering general discussion
#1

I have a lightly loaded jib crane that has a boom of about 12’ and the deflection at the end is about 2" under full load. This is about L/100.

Does anyone know of any regulations that put limits on the deflection. The mast or stanchion is a W section so depending on the orientation of the load the deflection is reduced to about 1-1/2".

There is no issue of the load trying to find the lowest point for safety reasons.

Dik

#2

Don’t know of any rule, but 2" at the end of a 12’ jib seems perfectly acceptable to me when it’s carrying the full rated load. Strength is the main criterion here; there is no gyproc to crack as a result of large deflection.

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#3

Thanks… I was thinking the same… CISC recommends L/150, but in a pinch as long as the strength is there and there are no secondary stablilty effects, I’m OK with it. I just don’t know if there are other authorities out there that have other guidelines.

Again, thanks,

Dik

#4

Well, if you want to be on the safe side, I’m guessing it would make very little difference in cost to satisfy the CISC recommendation, but I can’t see a good reason for it.

#5

It’s already built and is being used. It needs certification.

Dik

#6

Dik & BA:
The primary issues in that design are column and boom strength and stability. If it is working satisfactorily for them and your strength and stability calcs. check out it should be o.k. You could put a tension tie from the top of the boom back to the col. to improve stresses and deflections if needs be. One of the primary deflection issues is that they may be pushing the trolly up hill, fully loaded, from the tip of the boom, when they move a load.

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#7

Thanks… it’s already fabricated and in use. Unless I added to the jib, it is not possible to add a diagonal brace. In addition to ‘pushing the load uphill’, the vertical support has different stiffnesses for x and y axis so the load will want move downhill. could be a safety issue.

Dik

#8

Beefing up the column gives the biggest bang for the buck because the moment has maximum value for its full height.

#9

I’ll run with it as it is… I’ll do up a couple of qualifications and do up a PSR… and, I’m happy.

Dik