Page 166 - Masonry and Concrete

Masonry Construction Techniques
165
MASONRY CONSTRUCTION TECHNIQUES

laid directly on the units and lifted
slightly with the fingers after the mortar is
placed so that mortar can get underneath
the wires. All metal accessories which are
embedded in mortar joints should be kept
5
a minimum of 8-in. from the exterior face
of the joint so they are well protected from
wetting and corrosion.
Vertical steel reinforcement in a dou-
ble-wythe wall is placed in the cavity and
the masonry is built up around it. Spacers ALUMINUM VENT PLASTIC GRID
are used at periodic intervals to hold the FIGURE 5-26
reinforcing bars up straight and keep them
Weep hole accessories. (from Beall, Christine, Masonry
in the correct location. Spacers can also be
Design and Detailing, 4th edition, McGraw-Hill, New
used to support horizontal bars (Figure 5- York).
27). For single-wythe CMU walls with
steel reinforcement, special open-end units are made so that the block
can be placed around the vertical bars rather than threaded over the
top (Figure 5-28). Horizontal steel is placed in courses of special lintel
or bond beam blocks.

5.4.4 Control and Expansion Joints

Allowances must be made in brick and concrete masonry construction
for expansion and contraction of the units. All construction materials
expand and contract with temperature changes, some to a greater or
lesser degree than others. Clay brick also expands with the absorption
of moisture, and concrete masonry shrinks with loss of residual mois-
ture from the manufacturing and construction process. The exact loca-
tions of control and expansion joints will be affected by design features
such as openings, offsets, and intersections. In brick walls, expansion
joints should be located near corners because the opposing push of
intersecting walls can cause cracking. For both brick and concrete
masonry walls, joints should be located at points of weakness or high
stress concentration such as abrupt changes in wall height; changes in
wall thickness; columns and pilasters; and at one or both sides of win-
dows and doors. Freestanding walls of relatively short length that are
not connected to other structures may not require control or expansion
joints if they are free to expand and contract without restraint.

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