back up brick veneer. There have been many good papers on the topic.
Promulgated deflection limits include L/360 (steel stud mfgrs.), L/600
(BIA), and L/720 (Canadian Research).
Interestingly, the BIA guidance (TEK Note 28 B) limits the lateral
deflection of the stud to L/600 for "service" wind loads. Per BIA 28B,
"Therefore, to obtain sufficient backing stiffness, the allowable
out-of-plane deflection of the studs due to service level loads should be
restricted to L/600." But BIA does not define "service level loads".
For wind the IBC and ASCE 7 have us calculate the variable "p" that is
defined as the "design" wind pressure and is the 50 year Mean Recurrence
Interval (MRI). Serviceability is discussed in the ASCE 7 Section C6.5.5
and in the AISC Design Guide 3. The general consensus of the AISC is that
service level winds are 10 year MRI winds and are about 75% of the pressure
calculated from "design" 50 year MRI winds.
If the above logic is considered valid, the L/600 BIA limit at a "service"
10 year MRI wind would be about the same as a L/400 at a 50 year MRI
"design" wind load.
I know it is conservative to use the 50 year MRI for the L/600, but it also
increases the cost. I would welcome discussion and any performance studies
on systems constructed.
Building codes focus on life safety. This is a serviceability issue.
Regards,
Harold Sprague
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