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Re: Crane Girder Fatigue

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>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.
You'll want to check the structure against CMAA-70, which is the design 
standard for overhead cranes. This is one of those instances where 
service loads govern; LRFD is not what you want to use where you have 
ongoing fatigue requirements. Look real carefully for signs of abuse and 
signs of home-grown quick fixes. Bolts shouldn't be 'working loose' 
unless the thing was put up improperly or the original bolts broke and 
were replaced by lower grade fasteners or improperly torqued. 

If it were me I'd replace all the bolts and mag particle check the 
welds--at least the major connections. Presumably you're going to blast 
clean it and repaint, so you can do the welds and connections when it's 
all clean. You might also want to check the rail alignment.  The 
supporting structure may have used up a a lot of its fatigue life, and 
welds start to go after a while.

I'd also prepare myself with a regime of fasting and prayer. You can 
never tell what sorts of things actually happened during the previous 
service, and primary metals producers are characteristically hard on 
equipment. Just 'worked loose' may actually cover anything from 'It 
collapsed one day when the operators got stoned and started playing 
chicken,' to 'Scheduled maintenance is for candy-asses who don't have 
production quotas.' It's also a good idea to scrap all their old rigging 
or at least have it gone over by someone outside the firm with experience 
in such matters. 

Christopher Wright P.E.    |"They couldn't hit an elephant from
chrisw(--nospam--at)skypoint.com        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw