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Chris, 
Thanks for the reply.  You raised some of the same
questions I did plus a couple more good ones.  I find
sometimes when I ask these, that the problem gets
sorted out without coming back to me--here's hoping.
A little background: it is a 40tonne crane.  I designed
the trolley originally for another job, and my crane
customer then sold a second trolley to a customer who
had an existing 40 tonne dbl girder crane with which he
was dis-satisfied.  So they plunked the new trolley on
the old bridge.  That is the extent of my information,
other than it is yo-yoing.
Gary

On 15 Feb 2006 at 9:40, Christopher Wright wrote:

> 
> On Feb 15, 2006, at 6:39 AM, Gary Hodgson & Associates wrote:
> 
> > Just what I need--I got a call from a crane customer on
> > Monday whose customer is complaining about the crane
> > yo-yoing.  Does Timoshenko have anything on yo-yoing?
> My considerable experience with yo-yo's is that they have almost 
> nothing in common with cranes. Nor does Irvine mention it. So does the 
> hook load go to end-of-travel and then bounce back upward all on its 
> own? Or does the load just descend and stay there spinning until the 
> operator give the hoist a little tug? I bet Around the World or Walking 
> the dog is really quite something to see. (Sorry, couldn't resist. 
> Won't happen again);->
> 
> I'm assuming this is a bridge crane--is it? Sometime very early, you 
> should do a very careful inspection of the structure to make sure 
> nothing's broken. Structures tend to get bouncy when they're coming 
> apart or fracturing. If the motion has only recently become a problem, 
> the structure has changed, and loose bolts or broken welds could be 
> responsible. If the crane has been structurally soft since 
> installation, check it anyway because the continuous cycling tends to 
> loosen things. You might also check the rails to make sure they're 
> straight.
> 
> When you know that the structure isn't damaged, you want to try to see 
> if it's a control problem or a structural problem first. If it's a 
> bridge crane get an idea of the frequency and direction of motion and 
> any variation with load and trolley position. The softest element of 
> the load path is generally the bridge girders, so make yourself a quick 
> estimate of the corresponding frequencies, both vertical and horizontal 
> to see if there's a match. The frequency of motion will vary with 
> trolley location if the bridge girders are chiefly involved. Horizontal 
> (bridge travel direction) motion may involve either support deformation 
> or girder stiffness.
> 
> If you get lucky, you may find that the operation is at fault, either 
> because of a control malfunction that makes a drive stop suddenly or 
> operator technique. A structural problem may end up being a serious 
> nightmare, because it's not all that easy adding enough stiffness in 
> the right place to make a big difference. It also means bringing the 
> machine down and greatly affecting operation, which your customer won't 
> like.
> 
> Christopher Wright P.E. |"They couldn't hit an elephant at
> chrisw(--nospam--at)skypoint.com   | this distance" (last words of Gen.
> .......................................| John Sedgwick, Spotsylvania 
> 1864)
> http://www.skypoint.com/~chrisw/
> 
> 
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