MATERIALS AND SYSTEMS

ing economy in the building’s structure. However, this benefit is accompanied by several
concerns.
Steel studs can deflect considerably before the bending stress in them exceeds their ultimate
capacity. Brick veneer, on the other hand, deflects by a very small amount before the
mortar joints open. Open mortar joints weaken the wall and also increase the probability of
leakage, corroding the anchors.
Thus, the steel stud backup and brick veneer assembly performs well only if the stud
wall is sufficiently stiff. To obtain the necessary stiffness, the deflection of studs must be
controlled to a fairly small value. In fact, the design of a steel stud backup wall to resist the
lateral loads is governed not by the strength of studs but by their deflection.
The Brick Industry Association (BIA) recommends that the lateral load deflection of
steel studs, when used as backup for brick veneer assembly, should not exceed
stud span
600
where the stud span is the unsupported height of studs. For example, if the height of studs
(e.g., from the top of the floor to the bottom of the spandrel beam in Figure 26.7) is 10 ft,
the deflection of studs under the lateral load must be less than
110 * 122
= 0.2 in.
600
Increasing the stiffness of studs increases the cost of the assembly. Another concern with
steel stud backup is that the veneer is anchored to the backup only through screws that
engage the threads within a light-gauge stud sheet. Over a period of time, condensation can
corrode the screws and the corresponding holes in studs, making the screws come loose.
Condensation is, therefore, an important concern in a steel stud–backed veneer. A more
serious concern is that the anchor installer will miss the studs.
By comparison with steel studs, anchoring of brick veneer to a CMU backup does not
depend on screws; and hence it is more forgiving. Additionally, the anchors in a CMU
backup wall are embedded in the mortar joints, and if they are made of stainless steel, their
corrosion probability is extremely low.
Another advantage of a CMU backup wall is its inherent stiffness. To obtain a steel stud
backup wall of the same stiffness as a CMU backup wall substantially increases the cost of
the stud backup.
NOTE
CHAPTER 26
EXTERIOR WALL CLADDING
Defection of a Steel Stud
Wall Assembly
The design criterion of deflection
not exceeding span
divided by 600, suggested by
BIA, is the minimum requirement.
For critical buildings, a
more stringent deflection criterion,
such as span divided by
720 or span divided by 900, is
recommended by some
experts.
Steel stud manufacturers
generally provide tables for the
selection of their studs to conform
to the deflection criteria.
26.5 AESTHETICS OF BRICK VENEER
It is neither possible nor within the scope of this text to illustrate various techniques used
to add visual interest to brick veneer facades. However, a few examples are provided:
• Use of recessed or projected bricks in the wall, Figure 26.35.
• Use of bricks of different colors or combining clay bricks with other masonry materials
or cast concrete, Figure 26.36.
• Warping the wall, Figure 26.37.
FIGURE 26.35 Use of recessed or projected bricks with
different hues. The projections must be small so that the
core holes in bricks are not exposed. (Photo by MM.)
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