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Re: Crane Girder Fatigue

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'Appreciate your insight.  I have a copy of CMAA-70. 

The replaced bolts don't look like structural bolts, but more like
something you'd get at the local hardware store.  I won't say where this
crane is, but it is in an area where the "War of Northern Agression" is
still discussed.  "Those Yankees came in and burned all the buildings on
the waterfront.  Women were faintin', babies were cryin', it was *just*
awful."

I hadn't given much thought about "cowboys" operating this rig, but it's
possible.  The man in the cab operating a magnet doesn't have too much
"adult supervision"; all he has to do is get the scrap from point "A" to
point "B".  And I'm sure there's always the temptation to see how close you
can get to someone with a watch or a credit card.

Fortunately, the crane itself is being completely replaced.  The question
is whether to replace or re-use the existing crane support structure.  I
haven't crunched the numbers yet on the girder or the supports to see how
"tight" the original design was.

'Reminds me of the "Hagar, the Horrible" cartoon.  Lucky Eddie says, "Well,
we just finished another day of getting beat-up and shot-at."  Hagar
replies, "Yep, it really makes me feel sorry for those people with boring
desk jobs." -- Apologies to those who are deprived of Hagar ;-)

Fountain

----------
> From: Christopher Wright <chrisw(--nospam--at)skypoint.com>
> To: ? <seaint(--nospam--at)seaint.org>
> Subject: Re: Crane Girder Fatigue
> Date: Saturday, January 22, 2000 12:36 PM
> 
> >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)