Factors affecting the performance of brick veneer construction

The first topic focused on in this report is the height restriction imposed by the masonry standard for brick veneer on wood frame backing. The current US standard (ACI 530-05/ASCE 5-05/TMS 402-05 Building Code Requirements for Masonry Structures) does not allow brick veneer to extend more than thirty feet above the foundation when supported by wood framing. These prescriptive requirements are compared with those of the Canadian (CSA 304.1-04) and Australian (AS 3700-2001) masonry standards. The logic found for this height restriction is based on the vertical differential movement caused by moisture and thermal expansion of the brick veneer and moisture loss shrinkage of the wood framing. Structural analysis found that shrinkage of the wood framing primarily contributed to this vertical movement. Replacing sawn lumber framing with engineered lumber can result in significantly less shrinkage, therefore allowing for an increase in allowable height. In addition, this paper recommends extending the allowable height when the veneer is supported by shelf angles at each floor height or when the framing is stiffened against horizontal movement with appropriate sheathing. \t\t\tThe second topic considered is the requirement for horizontal wire joint reinforcement for brick veneer in Seismic Design Categories E and F according to IBC 2003. Previous research at other institutions has been investigated. Structural analyses for out-of-plane and in-plane loading demonstrate the theoretical capacity of the brick veneer without wire reinforcement compared to applicable loads. Next, an experimental program was designed to determine if the wire joint reinforcement was detrimental, beneficial, or had no effect on the performance of the wall system. First, quasi-static out-of-plane tests were performed on specimens with wood frame backing. These first tests compared the performance of the wall system with and without the joint reinforcement, as well as the ductility of the two systems when subjected to out-of-plane loading after the formation of diagonal shear cracking. Second, diagonal shear tests were performed on brick panels. These compared the performance of the brick veneer in diagonal shear with and without the joint reinforcement. Finally, flexural bond strength tests were performed. The variables considered in these tests included: the performance or absence of wire joint reinforcement, the type of mortar, the presence or absence of wall ties, and the type of wall tie used. Previous research conducted at other institutions has indicated that joint reinforcement is either unnecessary or detrimental to the performance of the wall system. The structural analyses performed in this investigation found that the brick veneer theoretically has the capacity to withstand applicable seismic loadings. In the experimental portion of this investigation, the wire did not appear to have any effect on the performance of this wall system. The walls typically failed due to the nail connecting the corrugated sheet metal tie to the wood framing pulling out. This investigation concluded that further research is needed on additional backup and connecting systems.

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