Why aren’t brick veneers required to meet the allowable flexural strength requirements of brick masonry listed in the building code?
In BIA Technical Note 28B, the stiffness of the backup wall is limited to L/600. Depending on the height of the wall, this figure can lead to stresses that greatly exceed the allowable flexural stresses in the masonry veneer.
Won’t the masonry veneer crack under these conditions?
Several physical and analytical studies have shown that many masonry veneer walls designed using the deflection limitations in Technical Note 28B can crack when subjected to design wind loads. However, since the masonry is acting only as a veneer, cracking does not create a structural problem.
The steel stud backup wall is designed to handle all out-of-plane loads. The masonry veneer supports only its own weight. Wind loads are transferred to the backup wall via the wall ties. If cracking occurs, the loads are carried by the backup wall. Cracks that form are likely hairline and generally not noticeable.
Water penetration through masonry walls during wind-driven rains occurs when moisture is blown against the face. During these times, the masonry wall is in compression as the system deflects inward, and as a result allows little water penetration.
In an experimental study performed at Clemson University by Russell Brown and J. O. Arumala published in the Second North American Masonry Conference, the flexural cracking did not affect water penetration. In fact, the only wall that experienced flexural cracking during testing actually had higher measured water penetration before cracking than it did after.