Masonry Magazine January 1977 Page.19
Requirements
Lateral support requirements for bearing and non-bearing walls as contained in the A41.1 Standard are as follows:
# 5.1. Ratio of Height or Length to Thickness
The ratio of unsupported height to nominal thickness or the ratio of unsupported length to nominal thickness (one or the other but not necessarily both) for solid masonry walls or bearing partitions of buildings shall not exceed 20 if of plain concrete or of solid masonry units if laid in Type A-1, A-2, B or C mortar, nor 12 if laid in Type D mortar; and, regardless of the type of permitted mortar used, shall not exceed 18 for walls of hollow masonry units or hollow walls. In computing the ratio for cavity walls, the value for thickness shall be the sum of the nominal thicknesses of the inner and outer wythes. In walls composed of different kinds or classes of units or mortars, the ratio of height or length to thickness shall not exceed that allowed for the weakest of the combination of units and mortars of which the member is composed.
# 5.2. Method of Support
Lateral support may be obtained by cross walls, piers, or buttresses, when the limiting distance is measured horizontally, or by floors and roofs when the limiting distance is measured vertically. Sufficient bonding or anchorage shall be provided between the walls and the supports to resist the assumed wind or other horizontal force, acting either inward or outward. Piers, buttresses and cross walls relied upon for lateral support shall have sufficient strength and stability to transfer the horizontal force, acting in either direction to adjacent structural members or to the ground. When walls are dependent upon floors or roofs for their lateral support, provision shall be made in the building to transfer the lateral forces to the ground.
# 6.3.2. Nonbearing Partitions
The distance between lateral supports of nonbearing partitions of masonry shall not exceed 36 times the actual thickness of the partition including plaster.
Figure 1 and Table 4 illustrate the maximum wall span/thickness ratios and methods of providing lateral support which are contained in the previously cited sections of the A41.1 Standard.
TABLE 4
Lateral Support Requirements-American National Standard A41.1-1953(R 1970)
| Type of Masonry Walls | Maximum Ratios L/t or H/t |
| ---------------------------- | --------------------------- |
| Solid masonry walls | 20 |
| Hollow unit masonry walls | 18 |
| Hollow walls | 18 |
| Nonbearing partitions | 36 |
For M. S. N and O mortar. Maximum ratio is 12 if K mortar is used. Thickness equal to sum of the nominal thicknesses of the inner and outer wythes. Thickness equal to actual thickness of partition including plaster.