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Re: Jib crane impact factor

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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.

       I hope this discussion is useful to you.

Regards,

Daryl

----- Original Message ----- From: "Drew Morris" <dmorris(--nospam--at)bbfm.com>
To: <seaint-seaosc(--nospam--at)mail-list.com>
Sent: Wednesday, July 03, 2013 12:59 PM
Subject: Re: [SEAINT-SEAOSC] Jib crane impact factor

Daryl, thank you for the information. I saw the impact loads in ASCE 7, but wasn't sure where my crane fit in. I have a question when using LRFD design with these factors. Is the factored live load Pu =

crane impact load factor * crane capacity

or 1.6 * crane impact load factor * crane capacity?

I have been using the latter formula, but with an impact factor 0f 2.0.

On 7/3/2013 10:40 AM, h.d.richardson(--nospam--at)shaw.ca wrote:
Drew,

I have two sources for you: ASCE-7; and the Canadian National Building Code. These are in partial agreement. Both specify 1.25 for cab or radio controlled cranes and 1.1 for pendent operated electric cranes. ASCE-7 specifies 1.0 for hand geared hand operated cranes; CNBC includes them with pendent operated cranes.

I have designed, checked out, or load rated several hundred cranes in

Truncated 657 characters in the previous message to save energy.

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