Masonry Magazine January 1977 Page.16
ALLOWABLE LOADS
8. Structural Clay Facing Tile, ASTM C 212-60 (1970).
9. Ceramic Glazed Structural Clay Facing Tile, Facing Brick, and Solid Masonry Units, ASTM C 126-71.
10. Hollow Load-Bearing Concrete Masonry Units, ASTM C 90-70.
11. Hollow Non-Load-Bearing Concrete Masonry Units, ASTM C 129-71.
12. Solid Load-Bearing Concrete Masonry Units, ASTM C 145-71.
Mortar
Section 3 of the A41.1 Standard requires mortar to conform to ASTM Specifications C 270, Mortar for Unit Masonry. When the A41.1 Standard was approved in 1953, the designations for the various ASTM mortar types were: A-1, A-2, B, C and D. In 1954, the designations in the ASTM C 270 Specifications were revised to: M, S, N, O and K, respectively. (Note: The new designations were apparently developed by dropping the alternate letters A. O. W and R from the phrase MASON WORK.) The current mortar type designations (M. S, N. O and K) will be used throughout this Technical Notes except in direct quotations from the ANSI Standard.
Material proportions for ASTM mortar types are listed in Table 1. The Brick Institute of America (BIA) recommends that mortars be composed of portland cement, lime, sand and water (see Technical Notes 8A).
The A41.1 Standard also requires that masonry be laid in mortar of the types specified in Table 2. BIA recommended general uses for mortars are discussed in Technical Notes 8, 8A and 8B.
General
Section 4.1 of the A41.1 Standard contains the following provisions pertaining to the determination of allowable loads on non-reinforced masonry construction:
4.1. General. In determining the stresses in the masonry, the effects of all loads and conditions of loading and the influence of all forces affecting the design and strength of the several parts shall be taken into account. Stresses shall be calculated on actual rather than nominal dimensions. Masonry construction shall be so designed and constructed that the allowable stresses prescribed herein are not exceeded.
Although not very specific, the intent of the first sentence of this section is to require designers to consider loading effects such as those due to wind loads and the eccentric application of vertical loads.
Allowable Stresses
Allowable compressive stresses permitted in the A41.1 Standard are given in Table 3. Although the allowable stresses given in this table are used in conjunction with the gross cross-sectional area of the masonry construction under consideration, it is the general intent that these allowable stresses (Table 3) be considered as allowable maximum fiber stresses, not allowable average stresses. In other words, if a brick masonry wall is to be subjected to an eccentrically applied vertical load, the allowable load should be determined so that the maximum compressive stress in the extreme fiber of the wall does not exceed the applicable allowable compressive stress given in Table 3.
TABLE 1
Mortar Proportions By Volume"
| Mortar Type | Parts by Volume of Portland Cement, or Portland Blast-Furnace Slag Cement | Parts by Volume of Masonry Cement | Parts by Volume of Hydrated Lime or Lime Putty | Aggregate, Measured in a Damp, Loose Condition |
| - | - | - | - | - |
| M | 1 | 1 | ... | Not less than 24 and not more than 3 times the sum of the volumes of the cements and lime used |
| S | 12 | 1 | 14 | |
| N | 1 | ... | over 14 to 1½ | |
| O | ... | 1 | over 1½ to 14 | |
| K | 1 | ... | over 14 to 22 | |
| | 1 | ... | over 212 to 4 | |
Based on Table 2. ASTM C 270-73, "Mortar for Unit Masonry."