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Re: Allowable Out-of-Plane Lateral Deflections of Masonry Veneers

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There is a difference. In the vertical case, it is purely a servicability concern since the metal studs provide the strength (the masonry is simply a veneer). The ACI 530 vertical deflection limit only applies to unreinforced masonry or masonry designed empirically. Therefore, the cracking is a strength issue since there is no reinforcement to carry the tensile stresses.
In fact, a speaker at an ACI seminar that I attended stated that if horizontal joint reinforcing is included in the masonry, the wall can be considered reinforced and the deflection limitations may be ignored.  I disagree with that statement since I do not include the effects of such joint reinforcing when designing a reinforced masonry wall.

I personally use an l/360 deflection limit for metal studs supporting brick veneer. Remember that brick veneer is a not a water barrier and must be backed up with a proper water-proofing system. If so, then any water that infiltrates through the cracks should be stopped by the water-proofing.
Adam Vakiener
Austell, GA

From: Scott Maxwell <smaxwell(--nospam--at)engin.umich.edu>
To: seaint(--nospam--at)seaint.org
Subject: Re: Allowable Out-of-Plane Lateral Deflections of Masonry Veneers

Matthew,

My best guess is that the lateral deflection of the veneer is considered a
servicability issues and not a life safety issue and as such the code does
not address it.  This does not completely make sense to me because in
reality the vertical deflection limit of L/600 or .3" is basically also a
servicability issue with little impact on life safety (not to mention that
there are other areas in general were the codes have gone beyond life
safety).

I will see if someone I know has a better answer for you.

Regards,

Scott
Adrian, MI


On Wed, 28 Feb 2007, Stuart, Matthew wrote:


> Back in the early 1980's I believe, when Architect's started to go with
> gage metal stud back up walls in lieu of CMU, the resulting flexibility
> of the metal studs resulted in a number of problems with masonry veneers
> primarily as a result of water infiltration through the mortar joints as
> the brick flexed to a point in which there was actual separation between
> the brick and the mortar at the joint interface. The metal stud industry
> and brick industry began pointing fingers at one another with the BIA
> responding with an H/600 criterion. Most design engineers at the time
> had trouble accepting this criterion because after all L/360 had worked
> for stucco finishes for some time. Never the less the H/600 got codified
> into ACI 530 which adopted the criteria for vertical deflection only.
>
>
>
> Does anyone have any insight into the current lack of connection between
> ACI 530 vertical deflection limitations and the current BIA
> recommendations for H/600 out-of-plane lateral deflection limitations?
> This is an issue because the ACI is a Code and the BIA provides
> recommendations only.
>
>
>
> D. Matthew Stuart, P.E., S.E., F.ASCE, SECB

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