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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 are applicable for bond beam blocks.
Dimension and Shape of Bond Beam Block
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 and webs
|Nominal Width (W) of Blocks, mm||Face Shell Thickness, minimum, mm||Web Thickness, minimum, mm||Equivalent Web Thickness, minimum, mm/linear m|
|76.2 and 102||19||19||136|
|305 and greater||38||29||209|
- Bond beam block width, height, and length are allowed to vary by 3.2 mm from the specified dimensions.
- Face shell and web thickness need to be in agreement with values provided in Table 1.
- Web thickness that is not in agreement with the value in Table 1 can be accepted- provided that equivalent structural capability has been established when tested.
- Bond 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.
- Minor 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.
Bond beam 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.
Moreover, bond 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 beam.
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 can also 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 is often 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.