Figure 8-26.-Installed precast concrete sills.
BOND BEAMS, LINTELS, AND SILLS
Bond beams are reinforced courses of block that
bond and integrate a concrete masonry wall into a
stronger unit. They increase the bending strength of
the wall and are particularly needed to resist the high
winds of hurricanes and earthquake forces. In
addition, they exert restraint against wall movement,
reducing the formation of cracks.
Bond beams are constructed with special-shape
masonry units (beam and lintel block) filled with
concrete or grout and reinforced with embedded steel
bars. These beams are usually located at the top of
walks to stiffen them. Since bond beams have
appreciable structural strength, they can be located to
serve as lintels over doors and windows. Figure 8-24
shows the use of lintel blocks to place a lintel over a
metal door, using the door case for support. Lintels
should have a minimum bearing of 6 inches at each
end. A rule of thumb is to provide 1 inch of bearing
for every foot of clear space. When bond beams are
located just above the floor, they act to distribute the
wall weight (making the wall a deep beam) and thus
help avoid wall cracks if the floor sags. Bond beams
may also be located below a window sill.
Modular door and window openings usually
require lintels to support the blocks over the openings.
You can use precast concrete lintels (figure 8-25,
view 1) that contain an offset on the underside
(view 2) to fit the modular openings. You can also
use steel lintel angles that you install with an offset on
the underside (view 3) to fit modular openings. In
either case, place a noncorroding metal plate under
the lintel ends at the control joints to allow the lintel to
slip and the control joints to function properly. Apply
a full bed of mortar over the metal plate to uniformly
distribute the lintel load.
You usually install precast concrete sills (figure
8-26) following wall construction. Fill the joints
tightly at the ends of the sills with mortar or a
PIERS AND PILASTERS
Piers are isolated columns of masonry, whereas
pilasters are columns or thickened wall sections built
contiguous to and forming part of a masonry wall.