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  • 1.  Allowable deflection of brick veneer

    Posted 06-23-2017 04:38 PM
    All codes seem to limit the deflection of brick veneer supported by lintels to L/600.
    Would this deflection limit also apply to a foundation supporting brick veneer?

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    Gary Boyd P.E., M.ASCE
    President
    Boyd Engineering Inc
    Magnolia TX
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  • 2.  RE: Allowable deflection of brick veneer

    Posted 06-26-2017 09:46 AM
    ​The  live load deflection limit of L/600 applies to a simple-span condition. The condition of fixity of the brick veneer at the support provided by the foundation being considered or at adjacent supports should be considered. I have always tried to be sure that vertical contraction joints are spaced to accommodate not only thermal  and moisture related shrinkage, but also to prevent fixity of the brick veneer at supports. If vertical joints in the brick veneer are not placed above the lintel at or near the lintel support, expect cracking to occur, if not from moisture or thermal variations, certainly from differential foundation settlement.

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    Robert Crossno P.E., LM.ASCE
    Civil Engineer
    Albuquerque NM
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    Original Message


  • 3.  RE: Allowable deflection of brick veneer

    Posted 06-26-2017 09:46 AM
    Hello, Gary.  I think it would be job dependent. If you're looking at a flexible wood foundation (historic restoration, perhaps), then absolutely.  If you're looking at typical, continuous concrete footings I don't think it would as important.  Consider this article from Structure Magazine: Design of Shelf Angles for Masonry Veneer.  Masonry veneer, while not something we often consider, has strength and stiffness (especially if joint reinforcing is provided).  If you can design the masonry veneer as a "beam" to span an opening, the lintel and its L/600 limit becomes a constructability item more than anything so you don't have to shore all of the openings (unless the lintel is bolted to a wood header - then it's a different story again).  When you apply this principle to the foundation, you should consider the short term deflections of the foundation.  If they are severe enough that it would be a concern, you're probably on piles and your grade beam isn't going to deflect under the weight of a story or two of brick.  (NOTE:  I'm NOT advocating not using lintels - I'm just using this to illustrate a concept as it is a valid application of engineering mechanics and analysis.)

    In short, I don't think it should be a matter of concern for a properly designed foundation.  That doesn't mean you shouldn't use judgement, of course, where you end up with an abnormally high load in a pile that could produce some differential deflections and movements (or similar cases).

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    Peter Hamilton EIT, A.M.ASCE
    Project Structural Engineer
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    Original Message


  • 4.  RE: Allowable deflection of brick veneer

    Posted 06-26-2017 09:47 AM
    Gary - Yes, the deflection controls would apply to any vertical support element in order to prevent excessive movement that would cause cracking in the brick. But I had never actually thought about the foundation specifically, so, good question.

    But that is a fair amount of foundation movement if you think about it, over a 50ft section of wall, L/600 = 1" of settlement. Regularly spaced movement joints in the brick would also help prevent cracking from these types of movements.

    Regards,
    Andrew

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    Andrew Kester, PE
    Florida
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    Original Message


  • 5.  RE: Allowable deflection of brick veneer

    Posted 06-26-2017 09:47 AM
    Brick doesn't know what is supporting it.  Rather, brick just knows that when its supports move too much, it cracks.  In our Boston-area practice, where old masonry buildings are common, we see foundation-movement-related cracking of brick as frequently as cracking due to excess lintel and beam deflections.

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    Steven Siegel M.ASCE
    Owner/Consult
    Siegel Associates, Inc.
    Newton MA
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    Original Message


  • 6.  RE: Allowable deflection of brick veneer

    Posted 06-26-2017 09:47 AM
    I would say yes.  The L/600 limit is designed to prevent cracking of the masonry.  Depending on the type of foundation, figuring out the correct "L" to use in computing the limit may be challenging.

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    Andrew Holmes P.E., L.S., M.ASCE
    Consulting Engineer
    Melbourne FL
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    Original Message


  • 7.  RE: Allowable deflection of brick veneer

    Posted 06-26-2017 11:14 AM
    Hi,
    I'd directly refer you to TMS402-13/ACI530-13/ASCE 5-13 Chapter 12 for both adhered and anchored veneer. This chapter has both prescriptive and design based requirements. I'm not sure what part of the country your from but the 2016 CBC has an update to the adhered section (1405.10). My understanding is this update is due to adhered veneer separating from the structure. Good luck

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    Christine Jansen P.E., M.ASCE
    Sacramento CA
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    Original Message


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