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Re: Camber

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Robert,
 
     <<   . . . spec'd 3/4" midspan camber in simple span channel to be reused in repeat bay forming system application.  >>
 
Assuming that this is a steel channel, you might want to consult the AISC manual as to camber and it's permanence.  Only about 75 percent of specified camber is likely to remain due to the release of stress due to the cambering operation.  As a steel fabricator of many years, I would not even begin to guarantee a specified ordinate of camber at mid span on an unsymmetrical section such as a channel.  As a practical matter, permanent camber is a pretty "iffy" thing at best depending upon the method of cambering and true yield tests from mill reports.
 
I note that that you base your assumptions purely upon wet concrete loading of 65 percent.  In the field it is not uncommon for there to be excessive point loadings due to pumping operations and additional loadings due to the workmen involved.  If the purlins are being handled with cranes, you might want to consider reverse shock loadings due to rough handling and stripping operations.
 
I would suggest that you examine the purlins upon delivery in a "as new" condition.  Specified camber on steel members less than 50 feet is subject to a tolerence of plus 1/2 inch and minus zero.  There is no real big problem with re-cambering a steel member with heat in the field.  I have done this many times.
 
J.M.2, Inc.
Jimmy  C.......(hisself)