Steel Stud vs. Wood Stud Brick Veneer Backup
Steel Stud vs. Wood Stud Brick Veneer Backup
(OP)
While researching options for a potential 16' brick veneer wall, we came across a deflection requirement in the Brick Institute Associations Tech Note 28 that only requires wood studs to be designed for L/240 for out-of-plane forces. This is significantly lower than the L/600 that we typically design for and in disagreement with their Tech Note 28B (Steel Studs) which requires L/600. I can't seem to find a reason for the difference other than wood design values are typically quite conservative. Has anyone run across this? Any ideas for the discrepancy? I have contacted BIA for their guidance in the matter and will follow up here if I hear back from them.
This project no longer has full height brick but it was a 16' tall building and was going to require a 2x10 wall (SPF No. 2) to meet the L/600 requirement that we normally follow.
Attached is Tech Note 28
This project no longer has full height brick but it was a 16' tall building and was going to require a 2x10 wall (SPF No. 2) to meet the L/600 requirement that we normally follow.
Attached is Tech Note 28






RE: Steel Stud vs. Wood Stud Brick Veneer Backup
RE: Steel Stud vs. Wood Stud Brick Veneer Backup
L/600 seems ridiculously ultra-conservative for out of plane.
The definition of a structural engineer: overdesign by a factor of 1.999, instead of the usual 2.
RE: Steel Stud vs. Wood Stud Brick Veneer Backup
A few things you can due to lessen the pain is to:
1) Take a 30% reduction in wind pressure for deflection
2) Use the tributary area of the stud as span^2/3
Both are permitted in ASCE-7
RE: Steel Stud vs. Wood Stud Brick Veneer Backup
I highlighted the important sections of the attachments that discuss the deflections. L/600 was given as the out-of-plane deflection of the steel backup studs.
RE: Steel Stud vs. Wood Stud Brick Veneer Backup
The fact you have drywall fastened on the inside obviously helps a lot, but I know of no method to calculate it.
The definition of a structural engineer: overdesign by a factor of 1.999, instead of the usual 2.
RE: Steel Stud vs. Wood Stud Brick Veneer Backup
A quote from the refrence --- "For comparison purposes, the crack width permitted for exterior exposure in reinforced concrete is given as 0.33 mm (CSA 2004e & CAC 2006). The previous issue of S304.1 (CSA 1994a) required a more stringent stud deflection limit of L/720 which resulted in average crack widths approximating those required for reinforced concrete. The current S304.1 (CSA 2004b) has liberalized the deflection limit to L/360 with the recognition that the wall as a system can accommodate any increase in water penetration that might result (CSSBI 2006b)"
I'm the same as Excel, I only design beyond the L/360 limit if required by the job specs.
Excel, point #2...should that be spacing^2/3?
http://www.cssbi.ca/Eng/_pdf/CSSBI-S19-08.pdf
RE: Steel Stud vs. Wood Stud Brick Veneer Backup
CANPRO
I think Excel was referring to the definition in ASCE 7-05 in which the tributary area for a single component (i.e. stud) "is the span length multiplied by an effective width that need not be less than one-third the span length" which equals L*L/3. For C & C loading, the actual wind pressure goes down as the area increases so it is a fairly helpful provision.
EXCEL
Thanks for the reminder. I had used those provisions to get down to a 2x8 but forgot to post that in the original post.
RE: Steel Stud vs. Wood Stud Brick Veneer Backup
I'm not trying to split hairs with the definition, but tributary and effective mean different things in this context.
RE: Steel Stud vs. Wood Stud Brick Veneer Backup
The definition of a structural engineer: overdesign by a factor of 1.999, instead of the usual 2.
RE: Steel Stud vs. Wood Stud Brick Veneer Backup
I am pretty sure it is (span^2)/3 for C&C members that have a long and narrow tributary area.