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Re: Structural steel--isolated joints

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>I knew you'd have good information... and you didn't even say anything to
>offend me,
Call it a senior moment. ;-> 

>Are you saying in this case lateral softness is a bad thing?
Low frequency systems tend to deflect more and I think you want to avoid 

It's not entirely apparent what stiffens what. Hard to imagine that 64000 
lb machine including dynamic amplification wouldn't take a 6 in pipe 
anywhere it felt like. I'm guessing, not having seen the site, but I'd 
say that when that crane shakes the displacement is just about what it 
would be if the pipe weren't there. The loading on the pipe is probably 
limited by the crane displacement, which is the only reason the column 
didn't fracture years ago. 

If you're using the HSS section to stabilize the crane girder, it has to 
be able to carry the corresponding loads. If you attach the two members 
elastically to limit the loading you defeat the stabilization. You might 
want to get some notion about the loading and displacement that the crane 
imposes in the HSS section to see if it's really doing anything. Part of 
the reason the crane shakes might be that the column doesn't actually 
stiffen it, rather it just rides along. Check the relative stiffness 
while you're at it, to see what supports what. I think if this were my 
problem I'd take a good look at the rest of the structure, to see if the 
vibration might be affecting the other supports. The rail misalignment 
really beats the hell out of the machine. It'd be a good idea to remedy 
that while you're about it.

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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