Bond beam blocks are concrete masonry units which are manufactured with reduced webs (Fig. 1) or with knock-out webs (Fig. 2); the knock-out webs are removed prior to the placement of the unit in the bond beam.
The purpose of reduced webs or removable sections is to install horizontal bond beam reinforcement easily. In general, dimensions and specifications of the normal hollow block masonry is applicable for bond beam blocks.
Dimension and Shape of Bond Beam
Bond beam block face dimensions of
203 mm by 406 mm, available in nominal thicknesses of 102, 152, 203, 254, 305,
356, and 406 mm. Specified dimensions of concrete masonry units are 9.5mm less
than nominal dimensions, so that 102 or 203mm module is maintained with 9.5 mm mortar
joints. ASTM C90 provides minimum face shell and web thicknesses for the
different sizes of concrete masonry units as in Table 1.
Table 1 Minimum thickness of Face shell
|Nominal Width (W) of Blocks, mm||Face Shell Thickness, minimum, mm||Web Thickness, minimum, mm|| Equivalent
minimum, mm/linear m
|76.2 and 102||19||19||136|
|305 and greater||38||29||209|
beam block width, height, and length are allowed to vary by 3.2 mm from the
shell and web thickness need to be in agreement with values provided in Table
thickness that is not in agreement with value of Table 1 can be accepted
provided that equivalent structural capability has been established when tested.
beam block shall be sound and free of cracks or other defects that interfere
with the proper placement of the unit or significantly impair the strength or
permanence of the construction.
cracks, incidental to the usual method of manufacture or minor chipping
resulting from customary methods of handling in shipment and delivery, are not
grounds for rejection.
blocks are used in the construction of bond beams in the masonry wall of a
structure. Bond beams are courses of block constructed with specially
manufactured masonry units which are designed to receive horizontal
reinforcement and grout.
beams can be used in masonry bearing walls to serve as horizontal members along
the top of the walls, tying the walls together. They can be used below a line
of bar joists, so that joist anchors can be embedded into the grout of the bond
Furthermore, bond beams are used as lintels over doors and windows. They sometimes are located at the bottom of walls that span over an opening to make a deep beam. Bond beam reinforcement also can be used for crack control. In this application, there must be a break between bond beams at the control joints in a wall.
Finally, the area of steel required for bond beams used for crack control should be greater than that required for joint reinforcement. This is because the yield strength of the bars often is slightly less than that of the joint reinforcement and because the walls will undergo greater shrinkage due to the wetting effect of the grout during construction.