Masonry Magazine May 1976 Page. 18
Design tables giving the maximum horizontal uniform load (psf) on simply supported concrete brick and block composite and cavity walls are also included in "Nonreinforced Concrete Masonry Design Tables." Structural design tables for reinforced concrete masonry walls built with 4-in. concrete brick and 4, 6 and 8-in. hollow concrete block are provided in "Reinforced Concrete Masonry Design Tables," NCMA, 1971. Basic allowable compressive loads on a typical 10-in. reinforced concrete brick and block wall are given in Table 5. These allowable loads must be reduced for wall slenderness by using the multiplication factor given in the footnote to Table 5.
Other Design Considerations
Information on the fire resistance, thermal and acoustical properties of concrete brick walls can be found in the following NCMA-TEK bulletins:
6-Estimating the Fire Resistance of Concrete Masonry.
35-Fire Safety with Concrete Masonry.
67-Tables of "U"-values for Concrete Masonry Walls.
9-Estimating Sound Transmission Class of Concrete Masonry.
69-Noise Insulation With Concrete Masonry.
Construction
Concrete brick walls (or concrete brick wythes) should be laid with full head and bed mortar joints. Except in cavity walls, the collar (vertical longitudinal) joints between the facing and backing wythes should also be filled with mortar or grout.
In multiple wythe walls, concrete brick should be bonded in accordance with one of the following methods:
a. Bonding with masonry headers- Where the facing and backing of masonry construction are bonded by means of masonry headers, a minimum 4 percent of the wall surface of each face shall be composed of headers extending not less than 3 inches into the backing. The distance between adjacent full-length headers shall not exceed 24 inches either vertically or horizontally. In walls in which a single header does not extend through the wall, headers from the opposite sides shall overlap at least 3 inches, or headers from opposite sides shall be covered with another header course overlapping the header below at least 3 inches.
b. Bonding with metal ties- The facing and backing (adjacent wythes) of masonry walls shall be bonded with corrosion resistant 3/16 inch diameter steel ties or metal wire of equivalent stiffness embedded in the horizontal mortar joints. There shall be minimum one metal tie for not more than each 4-1/2 square feet of wall area. Ties in alternate courses shall be staggered, and shall be embedded in face shell of hollow units. The maximum vertical distance between ties shall not exceed 24 inches, and the maximum horizontal distance shall not exceed 36 inches. Rods or ties bent to rectangular shape shall be used with hollow masonry units laid with the cells vertical. In other walls the ends of ties shall be bent to 90 degree angles to provide hooks not less than 2 inches long. Additional bonding ties shall be provided at all openings spaced not more than 3 feet apart around the perimeter and within 12 inches of the opening.
c. Bonding with prefabricated joint reinforcement- The facing and backing (adjacent wythes) of masonry walls shall be bonded with prefabricated joint reinforcement. There shall be one cross wire serving as a tie for not more than each two square feet of wall face area. The vertical spacing of the reinforcement shall not exceed 16 inches. The longitudinal wires shall be thoroughly embedded in the mortar.
d. Bonding with masonry bonders -Where two or more masonry units are used to make up a thickness of a wall, the inner and outer wythes shall be bonded at vertical intervals not exceeding 34 inches by transverse lapping of stretcher units at least 3 inches over the units below, or by lapping with units at least 50 percent greater in width than the unit below at vertical intervals not exceeding 17 inches.
NATIONAL CONCRETE MASONRY ASSOCIATION
P.O. Box 135, McLean, Virginia 22101