In-Situ Evaluation of Compressed Brick Veneer Using the Flatjack Technique

    Published: Jan 1999

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    The flatjack is a relatively nondestructive tool that allows engineers engaged in the repair and retrofit of masonry buildings (both historic and non-historic) to directly determine the in-situ state of compressive stress in masonry walls. The flatjack technique recently was used on a large modern apartment complex to quantify the compression in a brick veneer that was distressed and had questionable wind-load resistance. The compression in the veneer was due to a combination of concrete frame shrinkage and brick growth in a wall system that lacked horizontal control joints under the steel shelf angles. Although the compression caused spalling in the veneer, it also contributed beneficially to the walls' wind resistance. The amount of compression in the veneer was determined in several locations throughout the height of one elevation of the building using flatjacks. We found that the compression in the veneer was greater than the flexural tension produced by design wind loads (including a reasonable factor of safety), but below the compressive strength of the brick masonry. This finding allowed a repair solution that was modest relative to strengthening the wall for inadequate wind resistance. Prior to employing the flatjack in the field, we conducted in-house research to check the accuracy and reliability of the method, and develop our technique. We found that by altering gauge points from those locations prescribed by current ASTM standards to those recommended in recent research, greater accuracy could be obtained.


    flatjack, brick masonry, compressive stress, flexural stress, control joints, shelf angles

    Author Information:

    Bell, GR
    Principal and Staff Engineer, Simpson Gumpertz & Heger Inc., Arlington, MA

    Gabby, BA
    Principal and Staff Engineer, Simpson Gumpertz & Heger Inc., Arlington, MA

    Committee/Subcommittee: C01.11

    DOI: 10.1520/STP14206S

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