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Deflection Limits for Studs Backing Brick Veneer

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There has been some good discussion on the maximum deflections of studs that 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.

Harold Sprague

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