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Re: Jib crane impact factor

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Drew,
I can't add much to what has already been said, except that I have been designing cranes and runways since 1967 and I and others whom I know have never used Limit States Design (your LRFD). There is no real savings in it except in building structures. Daryl is right about crane abuse. I would also recommend a Canadian publication-"Crane Supporting Steel Structures Design Guide" authored by R A MacCrimmon. It was published by the Canadian Institute of Steel Construction (2nd edition) and was available free on-line and a hard copy for a fee. Bob MacCrimmon used LSD as that is code in Canada. The design guide recommended by Bill is excellent.
Gary
On 2013/07/04 12:31 AM, h.d.richardson(--nospam--at)shaw.ca wrote:
Drew,

There is an association called Crane Manufacturers Association of America (CMAA), whose name I couldn't recall for my earlier posting that specifies impact factors based on lift rates and many other things. I don't have a recent edition of their publication but an earlier edition specifically forbade the use of design methods based on ultimate strength. Their reasoning would seem to be related to the fact that cranes often fail due to fatigue.

Given that 1.25*1.5 = 1.875, your use of Pu = 2.0 is not unrealistic. Never-the-less, I would be cautious about relying completely on the use of factored loading to assess cranes. That said, a few years ago (make that several years ago) I had in my possession a code for the design of mill service cranes; I've forgotten the name of that specification; but you can probably find an up-to-date version of it via the internet. Now mill cranes lift the rated load several times per hour day in and day out. That particular code specified that cranes for mill service be designed using the AASHO bridge code for permissible procedures and allowable stresses for steel design.

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