to the stud deflection made little difference in the quantity of the
moisture that penetrated past the masonry. The important part for moisture
ingress of the wall as a system is the moisture barrier on the side opposite
the masonry in the air gap. Again, the L/720, L/1200, etc. made no
significant difference to the moisture penetration of the system.
Regards,
Harold Sprague
>From: "Dave Handy" <dhandy@trg.ca>
>Reply-To: <seaint@seaint.org>
>To: <seaint@seaint.org>
>Subject: Re: Deflection Limits for Studs Backing Brick Veneer
>Date: Tue, 14 Aug 2007 16:53:40 -0400
>
>It is interesting..possibly..to note that the latest Canadian code for
>masonry has reduced the deflection limit for flexible structural backing
>systems to L/360 providing the veneer is not used as part of the moisture
>management system. L/720 + tie deflection was used in the earlier code
>based upon the veneer being used to limit water penetration. We always have
>an air barrier membrane of some sort which would deal with any moisture
>that makes its way through the veneer.
>
>David Handy, P.Eng.
>
>----- Original Message ----- From: "Harold Sprague"
><spraguehope@hotmail.com>
>To: <seaint@seaint.org>
>Sent: Wednesday, August 08, 2007 12:48 PM
>Subject: RE: Deflection Limits for Studs Backing Brick Veneer
>
>
>>Bill,
>>I agree that L/600 is too stringent for out-of-plane bending for a
>>serviceability issue. The Canadadian research "Technics Steel Stud /
>>Brick Veneer Walls", by Trestain and Rousseau is one of the best studies
>>and drew from the McMaster University studies. The McMaster studies
>>actually constructed veneer stud walls and tested with wind pressure and
>>simulated rain.
>>
>>The result was that there was no increased system vulnerability due to
>>excessive leakage from the flexural cracking. The L/720, 600, 360 or
>>whatever does not elmininate flexural cracking. The deflection limit is
>>intended to reduce the flexural cracking size. But as the McMaster study
>>indicated, the size of the flexural cracking did not increase the system
>>vulnerability.
>>
>>What did have a more significant effect on the system were the elements to
>>control and manage the moisture that enters through the brick from rain
>>and dew point and provide corrosion resistance. The Technics article did
>>recommend L/720 for the full wind load, but (as stated earlier) actually
>>provided evidence that the crack width was not an issue for system
>>performance.
>>
>>A case can be made to use L/400 for the 50 year design wind (inferring the
>>L/600 for a 10 year service). I also suggest a look over the architect's
>>shoulder to see if the system is properly accounting for water management
>>and corrosion resistance.
>>
>>Regards,
>>Harold Sprague
>>
>>
>>
>>
>>
>>>From: <William.Sherman@CH2M.com>
>>>Reply-To: <seaint@seaint.org>
>>>To: <seaint@seaint.org>
>>>Subject: RE: Deflection Limits for Studs Backing Brick Veneer
>>>Date: Wed, 8 Aug 2007 07:12:18 -0600
>>>
>>>I feel that a reference to "service level wind loads" without a
>>>qualifier means code based wind loads without load factors applied.
>>>Thus, it would mean a 50-year wind load as written.
>>>
>>>But I do agree that the issue of "serviceability" is much more
>>>subjective. I think that a deflection limit of L/720 makes more sense
>>>for vertical deflection of lintels than for out-of-place deflection of
>>>masonry walls, due to greater wall flexibility in the out-of-plane
>>>direction. I would prefer to see the deflection limit defined for full
>>>code level, "service level wind loads", than define it for a lesser wind
>>>frequency, even if the lesser wind frequency is part of the basis for
>>>the defined limit. This just keeps requirements more "user friendly".
>>>
>>>Ultimately, I tend to feel that L/600 is too stringent a limitation for
>>>out-of-plane deflection.
>>>
>>>
>>>Bill Sherman
>>>CH2M HILL / DEN
>>>720-286-2792
>>>
>>>-----Original Message-----
>>>From: Harold Sprague [mailto:spraguehope@hotmail.com]
>>>Sent: Tuesday, August 07, 2007 9:40 AM
>>>To: seaint@seaint.org
>>>Subject: Deflection Limits for Studs Backing Brick Veneer
>>>
>>>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.
>>>
>>>Regards,
>>>Harold Sprague
>>>
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