Masonry Magazine April 1992 Page. 25
TABLE 2
Allowable Compressive Stresses
Allowable compressive stresses, 1,2 gross cross-sectional area, psi
Construction; compressive strength of unit gross area, psi
Type M or S mortar
Type N mortar
Solid masonry of brick and other solid units of clay or shale: sand-lime or concrete brick:
8000 or greater
350
300
4500
225
200
2500
160
140
1500
115
100
Grouted masonry, of clay or shale; sand-lime or concrete:
4500 or greater
225
200
2500
160
140
1500
115
100
Solid masonry of solid concrete masonry units:
3000 or greater
225
200
2000
160
140
1200
115
100
Masonry of hollow load bearing units:
2000 or greater
140
120
1500
115
100
1000
75
70
700
60
55
Hollow walls (noncomposite masonry bonded³)
Solid units:
2500 or greater
160
140
1500
115
100
Hollow units
75
70
Stone ashlar masonry:
Granite
720
640
Limestone or marble
450
400
Sandstone or cast stone
360
320
Rubble stone masonry
Coarse, rough or random
120
100
Linear interpolation for determining allowable stresses for masonry units having compressive strengths which are intermediate between those given in the table is permitted.
21 psi 6.9 kPa
Where floor and roof loads are carried upon one wythe, the gross cross-sectional area is that of the wythe under load; if both wythes are loaded, the gross cross-sectional area is that of the wall minus the area of the cavity between the wythes. Walls bonded with metal ties shall be considered as noncomposite walls unless collar joints are filled with mortar or grout.
These allowable stresses only pertain to vertically applied loads reasonably centered on the wall. Any influence of an eccentrically applied load is limited by the minimum wall thickness and maximum lateral support requirements.
Lateral Support (9.5)
Chapter 9 contains arbitrary limits on the ratios of wall thickness to distance between lateral supports. These limits provide controls on the flexural tension stresses within the wall and limit possible buckling under compressive stresses. Maximum h/t or l/t ratios and minimum thickness used for determining distance between lateral supports are consistent with past masonry standards. Definitions for height (h), length (1) and thickness (t) for use in the allowable lateral support ratios are as follows: h the vertical distance or height between lateral supports; 1 the horizontal distance or length between lateral supports; and the nominal thickness of the masonry wall under consideration. ACI 530/ASCE5 does not provide guidance for computing the thickness of masonry bonded hollow walls or cavity walls bonded with metal ties. BIA suggests that the value for thickness be the sum of the nominal thicknesses of the inner and outer wythes.
TABLE 3
Wall Lateral Support Requirements
Construction
Maximum it or hit
Bearing walls
Solid or solid grouted
20
All other
18
Nonbearing walls
Exterior
18
Interior
36