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Crane Girder Fatigue

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I'm looking at a 20 year old foundry bridge crane runway -- 'Not a huge
capacity -- 10T main, 5T auxiliary, but fairly severe service.  I make it
what used to be called "Class D, HEAVY DUTY SERVICE", from an old Whiting
Crane Handbook.

I've visited the site.  The owner has replaced many of the structural
bolts, because they'd "worked loose".  The steel (crane girder & columns)
does not show any immediately obvious distress -- cracked welds;  cracking
in the top flange cap channel...  The crane itself is being replaced,
because rehab will cost nearly as much as replacement.

I'll be analyzing the crane girder, the attachments, the supports and the
overall stability of the structure.

Using Appendix K, AISC, ASD, 9th Edition, TAbel A-K4.1, I place this crane
in Loading Condition 4. 

Seismic is not likely a factor, since it's Zone 1.

Are there any traps I should look out for?

Thanks,

Fountain E. Conner, P.E.
Gulf Breeze, Fl. 32561