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Re: l/600 or l/720 brick veneer light gage back-up

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Ken,
 
I can't find the article off hand, but I believe that I remember reading something to the effect that the deflection limits were stringent to mitigate the development of micro-cracks in the bed joints to eliminate water infiltration.  The NRC Canada comes to mind, but again, that's the best guess if I had to Google it again.  As far as the appropriate design wind load, I would only add that it seems excessive to design a servicibility criteria like this for the highest possible wind and the most stringent of deflections.  Perhaps the 0.7 in note f is established for this very reason.  I would like to see the commentary on this note, if there is any.
 
When I worked for one of your occasional light gage panel clients in Bethlehem, we always used L/600 for C&C loads.  That was as much to err on the side of caution, as it was because we were certain it was the right thing to do.  But I must admit, doing so cost the company a lot of money and a lot of arguments because 12ga studs and gage tube steel aren't cheap, especially when they can't even get a common tech screw to penetrate.
 
If you find anything more, please let me know.  And I also notice that 1604.3.4 states that masonry deflection shall not exceed that permitted by ACI 530.
 
Jim Wilson
Stroudsburg, PA

Ken Peoples <kspeoples(--nospam--at)lvta.net> wrote:
I know that BIA recommends l/600 to l/720 for a brick veneer back-up deflection limitation.  They say "for service loads".  What I am not sure about is what the design wind pressure for this condition should be.  Should this just be based on the same component and cladding design load used for the strength design of the studs or can it be a reduced wind load.  Table 1604.3 of IBC 2003 indicates that the deflection limit for exterior walls with brittle finishes should be l/240 and footnote f indicates that the load may be 0.7 times the design component and cladding loads.  This seems to be quite different form BIA's recommendation of l/600.  Perhaps a brick veneer is not considered a brittle finish?
 
Is the l/600 or l/720 specifically required somewhere else in the IBC?
 
Thanks for your help.
 
Best regards,
 
 
Ken
 
Kenneth S. Peoples, P. E.
LVTA
Lehigh Valley Technical Associates, Inc.
1584 Weaversville Road
Northampton, PA 18067
 
Phone: 610-262-6345
Fax:610-262-8188
Email: kpeoples(--nospam--at)lvta.net


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