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

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Daryl and all:

The last version of CSA S304.1-04 states that L/360 is sufficient for backing systems for brick veneer. They do go on to say that if the brick is used as part of the moisture management system, tighter deflection limits can be specified. I like this ideology better than saying L/720 for everything because we always use other elements to handle the moisture. This has made the difference between 10" block and 12" block in many cases of tall block walls. I have used the L/720 value since I started working with steel studs, however. I would be concerned with getting too "loose" with the steel stud backup because there are so many other factors allowing deflection with that type of wall, ie. bend of track at the base and at deflection track support details at the tops of walls.

regards,
David Handy, P.Eng.


----- Original Message ----- From: "Daryl Richardson" <h.d.richardson(--nospam--at)shaw.ca>
To: <seaint(--nospam--at)seaint.org>
Sent: Thursday, March 01, 2007 1:34 PM
Subject: Re: Allowable Out-of-Plane Lateral Deflections of Masonry Veneers


Adam, and others,

L/360 is not an adequate limit on brick veneer walls! L/600 would seem tolerable; L/720 is probably preferred.

Following is a Canadian history lesson to back up the above statement. Those not interested should go on to the next posting.

A good many years ago Canadian engineers and architects were using metal stud and brick veneer exterior walls extensively due to their cost advantage. However, there came to be a lot of insurance claims; as a result ENCON (the insurance underwriter for most engineers and architects in Canada) wrote to all of their policy holders (myself included) strongly recommending that the system no longer be used. CSSBI ( Canadian Sheet Steel Building Institute) took exception to this for obvious reasons and countered with a proposal to use L/720 as the standard AND to have all metal stud wall system installations subjected to structural engineering supervision, including stamped shop drawings and stamped engineering inspection reports. As a result, L/720 has become the standard for most engineers I know. Stamped shop drawings and inspection reports are generally provided by an engineer retained by the contractor rather than the EOR, a practice I am not in complete agreement with, however, that is the subject of another posting.

Regards,

H. Daryl Richardson

----- Original Message ----- From: "Adam Vakiener" <avakiener(--nospam--at)southernae.com>
To: "SEAINT" <seaint(--nospam--at)seaint.org>
Sent: Thursday, March 01, 2007 5:43 AM
Subject: Re: Allowable Out-of-Plane Lateral Deflections of Masonry Veneers


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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