Masonry Magazine February 1979 Page. 28
This standard also requires that where floors or roofs are used to provide lateral support to a masonry wall, anchorage shall be designed to resist a minimum force of 200 lb per lineal ft in any direction.
Panel Walls
Panel or exterior nonload-bearing walls must be designed to safely resist wind, seismic or other lateral loads. Allowable heights for nonload-bearing concrete masonry walls (laterally supported at top and bottom) and subject to wind are shown in Figure 1. Allowable horizontal spans for nonload-bearing walls are shown in Figure 2. If panel walls are supported along more than two sides, lateral load can be carried in both vertical and horizontal spans. Maximum spans for non-reinforced walls simply supported on four sides are presented in References 3 and 4. If the walls are required to exceed the spans shown in Figures 1 and 2, the walls may be designed as partially reinforced walls in accordance with the design requirements included in Reference 5. Maximum wall heights for reinforced nonload-bearing walls subject to wind are given in Table 3.
Bearing Walls
Design Requirements. In accordance with the NCMA Standard, allowable axial loads on concrete masonry bearing walls are computed by the following formulas:
Non-reinforced: 0.200
Reinforced: A E. (1)
P225( (2)
where fm= compressive strength of masonry,
h = effective height,
t= effective thickness,
Annet cross-sectional area for hollow units and gross cross-sectional area for solid units (non-reinforced walls); and net mortar bedded area plus area of grout-filled cells for reinforced walls.
Walls subject to combined axial and flexural loading must be proportioned so that the quantity
+
Fa Fm
where fa shall not exceed 1 Eq. (3)
Fa computed axial stress,
allowable axial stress (see Eq. 1 and 2),
fm computed flexural compressive stress,
Fm allowable flexural compressive stress: 0.30 fm for non-reinforced masonry and 0.33 fm for reinforced masonry.
In non-reinforced walls, where the virtual eccentricity does not exceed 1/3 the thickness for walls of solid units or the value which will produce tension in walls of hollow units, the fiber stresses, fa and fm, shall be determined by recognized straight line theory. Where the virtual eccentricity in solid unit walls produces tension (e greater than t/6 but less than t/3), the cross-section used for determining stresses shall be based on a cracked section with the assumption that the masonry does not resist tension. For hollow unit walls, tension will not occur as long as the virtual eccentricity (e) does not exceed S/A where S = section modulus and A net area.
Where the virtual eccentricity exceeds the above limits, the fiber stress is determined by recognized straight line theory using the uncracked mortar bedded area. Such walls must be proportioned so that fm-0.75 fa does not exceed F where F₁ allowable tensile stress permitted in non-reinforced masonry
Design Tables. Maximum wall heights for non-reinforced hollow unit concrete masonry walls subjected to concentric loads and wind are given in Table 4. Allowable vertical axial loads for reinforced concrete masonry walls of various heights and subject to wind are given in Table 5. Additional design tables covering a wide variety of concrete masonry wall construction and load combinations are contained in Reference 6 and 7.
CITED REFERENCES
1. "Empirical Design of Concrete Masonry Walls," TEK 73, NCMA, 1975.
2. "Concrete Masonry Handbook for Architects, Engineers, Builders," F. A. Randall, Jr. and W. С. Panarese, Portland Cement Association, 1976.
3. "Design of Concrete Masonry Warehouse Walls," TEK 37, NCMA, 1972.
4. "Engineered Concrete Masonry Warehouses," TEK 89, NCMA, 1977.
5. "Partially Reinforced Concrete Masonry Walls," TEK 63, NCMA, 1975.
6. "Reinforced Concrete Masonry Design Tables," H. Toennies, NCMA, 1971.
7. "Nonreinforced Concrete Masonry Design Tables," H. Toennies, NCMA, 1971.
ADDITIONAL REFERENCES
8. "Engineered Concrete Masonry- Wind Loads," TEK 24, NCMA, 1971.
9. "Concrete Masonry Warehouse Walls-How to Buy a Warehouse," TEK 32, NCMA, 1971.
10. "Eccentric Loading of Nonreinforced Concrete Masonry," TEK 31, NCMA, 1971.
11. "Concrete Masonry Construction Details-Commercial Buildings," TEK 94, NCMA, 1977.