Free Standing Jib Crane bolted to floor
Free Standing Jib Crane bolted to floor
(OP)
I am reviewing a jib crane right now where the manufacturer is claiming that it can be just bolted to the floor (slab on grade) as long as the slab is of a certain thickness and a certain width with no cracks or joints within that area. The problem I see is that they are using a factor of safety of overturning of about 1.2 versus 2.0. They seem to be out there telling clients that no foundation is required.
Thoughts?
Thoughts?






RE: Free Standing Jib Crane bolted to floor
RE: Free Standing Jib Crane bolted to floor
RE: Free Standing Jib Crane bolted to floor
RE: Free Standing Jib Crane bolted to floor
What is the crane capacity?
Is this a single leg crane or multiple leg?
How thick is the slab?
Mike McCann
McCann Engineering
RE: Free Standing Jib Crane bolted to floor
Are they basing the FS on already highly factored loads in an LSD or similar scenario?
In some cases I've seen low factors of safety on overturning are acceptable, but the loads have already been factored well above anything reasonably expected.
RE: Free Standing Jib Crane bolted to floor
It's very cheap to saw cut out the slab on grade, dig down and install a proper size and depth cast in place concrete footing with anchor bolts. For the amount of money it would cost, especially compared to the jib crane, I'd strongly recommend it.
RE: Free Standing Jib Crane bolted to floor
Now that those F.S. have been removed from the codes and replaced with load combinations, there is not a load combination for uplift or overturning caused by gravity loads (unless you want to use 0.6 + W), so I just revert back to what we have used for many years, FS = 2.0.
RE: Free Standing Jib Crane bolted to floor
RE: Free Standing Jib Crane bolted to floor
I see nothing wrong with applying the old 2.0 safety factor for overturning, based on specified loads where dead loads govern. However, in a crane design the main overturning loads are live loads, so it is possible a FS of 1.2 is based on 0.8 or 0.85 time the dead loads resisting overturning and 1.5 or 1.7 times the live loads causing overturning. 1.2*1.5/0.85 = 2.1, so if based on factored loads the 1.2 may well be acceptable.