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Re: Contact loads from moving loads

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Joseph,

The problem is easy, but not really.  <grin>

If you know how quickly the log stops from 200 ft/s to zero and over what
distance, then the problem is relatively simple.  You would be able to
determine the decleration and multiply that by the mass of the log to get
your force.

But, the problem is that determining how quickly it stops and over what
distance is not easy.  Thus, the problem becomes difficult.  As Michael
pointed out, it will be come a function of the stiffness of the stop (i.e.
is it really stiff such that it does not compress much and stops the log
rather quickly or somewhat soft so that the log takes a little longer to
stop over a longer distance).

Beyond the above, I am not much help.  I could only suggest that you take
a "reasonable" guess.  If you take a guess as to the distance that it
takes to stop (i.e. how much the stop compresses), you should be able to
get an approximate decleration value.  But, to really be accurate, you are
talking about dealing with the mechanics and dynamics of non-rigid
bodies...stuff that make my head hurt (and not because my non-rigid head
would rather be bounced on the more rigid desk than think of such things).

HTH,

Scott
Ypsilanti, MI


On Tue, 7 Oct 2003, Joseph Grill wrote:

> Gentlemen and ladies of this fine list,
>
>
> I know I am taking you California engineers away from the election this evening, but I need to ask a question that I am not too familiar with.  I have a situation where a 6200# log is moving along a support driven by chains.  The log will contact a stop mechanism which is supposed to stop the log.  The log will be moving at 200 ft/min.  I need to calculate the force on the stop.  Can you give me any help or send me to a reference that I hope I have that may explain what I need to do.  I have been looking at a 25 year old dynamics book from college, but to be honest it isn't helping me very much.  It is a little late this evening, but I need to get going on it in the morning.  I can scratch out some numbers which I think will be pretty conservative, but would like some other input if I can get it.  The stop mechanism needs to be designed after the force is determined.
>
> Thanks,
> Joseph R. Grill



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