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Re: FOS for von-Mises stress criteria

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On Jan 14, 2006, at 6:01 AM, Gary Hodgson & Associates wrote:

I have been called to look at UR
runways where the bottom flange was drooping down, curled down to use
a less technical term.  Checking them against the CMAA
formulas showed they were inadequately sized.
Or maybe were overloaded. It's been known to happen in crane support design. Easy to justify by a 3 step process:.

1. Shop foreman isn't getting the production rate, asks plant engineer how to increase crane capacity. 2. Plant engineer figures there's a 1.6 safety factor on the rails and opines that foreman can increase the load by 1.6 for a little while. 3. Little while becomes daily; 1.6 becomes 2; plant engineer retires and foreman gets a new job. The loading increase becomes 'perfectly OK, we do it all the time with no problems' until the trolley slips off the rails because the flanges are bent too far under the overload.

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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