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Re: Structural dynamics of overhead cranes

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>Can someone help me by providing some guidances or recommendations for
>considering dynamic requirements in safe design of overhead cranes?  I've
>seen that there is no much legislation or literature about it.
I've been in the biz for about 20 years, and I know of nothing. CMAA is 
out standard of choice. It has nothing about dynamics nor does the ASME 
nuclear standard for cranes. One thing I have found is that once you 
decide on the span of the machine, the natural frequency is pretty much 
fixed. It's very difficult to add stiffness without adding mass so that 
the frequency doesn't change much.

The frequency limit you collected from the Euronorm is about what I've 
found for all the machines I ever worked on. You should also remember 
that there is no such thing as 'the' frequency. The girder system alone 
has 3 or 4 important modes involving a lot of mass and significant 
displacements. The stiffest mode is usually vertical deflection, but 
lateral movement and rocking (trolley rocks about the girder spanwise 
axis are also biggies.

I did one machine where frequency was a big issue for controllability. We 
started out with a twin girder trolley arrangement and went to a single 
box beam with the trolley attached in a sort of 'side-saddle' 
arrangement, loading the box beam in torsion. We ended ended up making 
the machine lighter that way and lots stiffer compared with two I section 
girders. which had no lateral stiffness to speak of.

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

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