Masonry Magazine June 1973 Page. 34
Research
The results of recent structural research investigations have confirmed that the strength of composite masonry wall systems depend not only on the strengths of the wythes of which they are composed but also on the manner in which these wythes interact. In order for composite wall systems to act as a monolithic section, shear forces acting in the plane of the wall between the various wythes must be effectively resisted. Accordingly, it is extremely important in composite wall construction (where the wall is designed as a monolithic section) to insure that the collar (vertical longitudinal) joint between the facing and backing wythes is completely filled with mortar or grout.
A comparison of ultimate and allowable loads on 10-inch composite walls built with 4-inch clay brick and 6-inch hollow concrete block is given in Table 2. As can be noted, the ratio of ultimate load to allowable load exceeds 5.3 for each of the different loading conditions.
"Strength of Masonry Walls Under Compressive and Transverse Loads," Yokel. Mathey and Dikkers. National Bureau of Standards, BSS 34, March, 1971.
TABLE 2.
Comparison of ultimate and allowable loads on 10-inch composite walls built with 4-inch clay brick and 6-inch hollow concrete block.*
| Eccentricity of loading † | Average ultimate load, kip (2 specimens) | Allowable design load, kip** | Ratio: Ultimate load Allowable load |
|---|---|---|---|
| 0 | >600 | 114 | >5.3 |
| 0.82-in. (toward brick face) | 568 | 91 | 6.2 |
| 0.55-in. (toward block face) | 335 | 55 | 6.1 |
| 3.10-in. (toward block face) | 180 | 20 | 9.0 |
* Data based on tests conducted by National Bureau of Standards. Walls were 9.5-inches thick. 32-in. wide and 90-inches high. Brick wythe was 3.6-in. thick and block wythe was 5.6-in. thick and were tied together with metal ties. Strength of brick f'm = 4515 psi (prism tests) and strength of block. f'm = 1473 pai (prism tests); a = 2.6: type 5 morior.
† Walls had pinned ends (top and bottom) and eccentricity was measured from centroidel axis which was located 2.07 in. from brick face.
** Based on "Specification for the Design and Construction of Load-bearing Concrete Masonry-NCMA, 1970."
NATIONAL CONCRETE MASONRY ASSOCIATION
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