TEK 14-01B
SECTION PROPERTIES OF CONCRETE MASONRY WALLS
INTRODUCTION
Engineered design of concrete masonry uses section properties to determine strength, stiffness and deflection characteristics. These design philosophies are summarized in Allowable Stress Design of Concrete Masonry, Strength Design Provisions for Concrete Masonry and Post-Tensioned Concrete Masonry Wall Design (refs. 1, 2, 3).
SECTION PROPERTIES
Tables 1 through 13 summarize section properties of grouted and ungrouted 4-, 6-, 8-, 10-, 12-, 14- and 16-in. (102-, 152-, 203-, 254-, 305-, 356- and 406- mm) wide concrete masonry walls, based on:
- standard unit dimensions are based on the minimum face shell and web thickness requirements of Standard Specification for Loadbearing Concrete Masonry Units, ASTM C90-06 (ref. 4) as shown in Figure 1, except as noted in Tables 8 through 13. Note that prior to ASTM C90-06, two minimum face shell thicknesses for units 10-in. (254-mm) and wider were specified. With the introduction of ASTM C90-06, the two face shell thicknesses were replaced with one minimum thickness requirement (1¼ in. (32mm)). See Reference 5 for further information. Tables 10 through 13 can be used for section properties of units complying with previous editions of ASTM C90.
- the nominal face dimensions of all units are 16 in. long by 8 in. high (406 by 203 mm),
- all mortar joints are ⅜ in. (9.5 mm) thick,
- all mortar joints are the same depth as the thickness of the face shell or web on which they are placed,
- for ungrouted and partially grouted masonry, all units have a symmetrical cross-section, square ends and two cores (with the exception of architectural features such as scores, ribs and split surfaces). Note that the section properties listed can be conservatively applied to open-end units (see Figure 2) that are either partially grouted or solid grouted, since by code the cells with the open end must be grouted.
The tables include both net and average properties. Net section properties (An, In and Sn) are calculated based on the minimum net cross-sectional area of an assemblage. These values are related to the critical section when determining stresses due to an applied load (refs. 6, 7). Average section properties (Aavg, Iavg, Savg and ravg) correspond to an average cross-sectional area of an assemblage, and are used to determine stiffness or deflection due to applied loading (refs. 6, 7).
The net and average horizontal section properties are listed in Tables 1a, 2a, etc., while vertical section properties are listed in Tables 1b, 2b, etc. For vertically spanning walls, horizontal section properties are calculated along a horizontal axis parallel to the plane of the masonry (axis X-X in Figure 3). For horizontally spanning walls, vertical section properties are calculated along a vertical axis parallel to the plane of the masonry (axis Y-Y in Figure 3).
In addition to section properties based on the standard unit dimensions shown in Figure 1, Tables 8 and 9 list section properties of walls constructed using 8-in.(203-mm) units with thickened face shells. These units are often specified to achieve higher fire ratings. Table 10 lists section properties of walls constructed using 10-in. (254-mm) units with 1⅜ in. (35 mm) face shells, the minimum required prior to ASTM C90-06. Similarly, Tables 11, 12 and 13 list section properties of walls constructed using 12-, 14- and 16-in. (305-, 356- and 406-mm) units, respectively, with 1½ in. (38 mm) face shells.
Figure 1—Specified Block Dimensions and Minimum Face Shell and Web Thicknesses (ref. 4)
Figure 2—Open-End Units
METRIC CONVERSIONS:
in. x 25.4 = mm
in.²/ft x 2,117 = mm²/m
in.³/ft x 53,763 = mm³/m
in.4/ft x 1,365,588 = mm4/m
Table 1—4-inch (102-mm) Single Wythe Walls, ¾ in. (19 mm) Face Shells (standard) (C)
Table 2—6-inch (152-mm) Single Wythe Walls, 1 in. (25 mm) Face Shells (standard)
Table 3—8-inch (203-mm) Single Wythe Walls, 1¼ in. (32 mm) Face Shells (standard)
Table 4—10-inch (254-mm) Single Wythe Walls, 1¼ in. (32 mm) Face Shells (standard)
FOOTNOTES:
A Net cross-sectional properties determined from a vertical plane that coincides with the face shells of the units. Net cross-sectional properties are to be used for determining stress and strain resulting from the application of load.
B Average cross-sectional properties determined from two vertical planes calculated as the average of the net and solid properties. Average cross-sectional properties are to be used for determining stiffness and deflection of an element.
C Because of the small core size and resulting difficulty consolidating grout, 4-in. (102-mm) units are rarely grouted.
Table 5—12-inch (305-mm) Single Wythe Walls, 1¼ in. (32 mm) Face Shells (standard)
Table 6—14-inch (356-mm) Single Wythe Walls, 1¼ in. (32 mm) Face Shells (standard)
Table 7—16-inch (406-mm) Single Wythe Walls, 1¼ in. (32 mm) Face Shells (standard)
Table 8—8-inch (203-mm) Single Wythe Walls, 2 in. (51 mm) Face Shells (nonstandard)
Table 9—8-inch (203-mm) Single Wythe Walls, 1⅜ in. (35 mm) Face Shells (nonstandard)
Table 10—10-inch (254-mm) Single Wythe Walls, 1⅜ in. (35 mm) Face Shells (nonstandard)
Table 11—12-inch (305-mm) Single Wythe Walls, 1½ in. (38 mm) Face Shells (nonstandard)
Table 12—14-inch (356-mm) Single Wythe Walls, 1½ in. (38 mm) Face Shells (nonstandard)
Table 13—16-inch (406-mm) Single Wythe Walls, 1½ in. (38 mm) Face Shells (nonstandard)
Figure 3—Horizontal and Vertical Cross-Sections
NOTATION:
Aavg = average cross-sectional area of masonry, in.² (mm²).
An = net cross-sectional area of masonry, in.² (mm²).
Iavg = moment of inertia of average cross-sectional area of masonry, in.4 (mm4).
In = moment of inertia of net cross-sectional area of masonry, in.4 (mm4).
ravg = radius of gyration of the average cross-sectional area of masonry, in. (mm).
Savg = section modulus of the average cross-sectional area of masonry, in.³ (mm³).
Sn = section modulus of the net cross-sectional area of masonry, in.³ (mm³).
References
- Allowable Stress Design of Concrete Masonry, TEK 14-7B. National Concrete Masonry Association, 2009.
- Strength Design Provisions for Concrete Masonry, TEK 14-4B. National Concrete Masonry Association, 2008.
- Post-Tensioned Concrete Masonry Wall Design, TEK 14-20A. National Concrete Masonry Association, 2002.
- Standard Specification for Loadbearing Concrete Masonry Units, ASTM C90-06. ASTM International, 2006.
- ASTM Specifications for Concrete Masonry Units, TEK 1-1F. National Concrete Masonry Association, 2012.
- International Building Code 2003. International Code Council, 2003.
- International Building Code 2006. International Code Council, 2006.
NCMA TEK 14-1B, Revised 2007.
NCMA and the companies disseminating this technical information disclaim any and all responsibility and liability for the accuracy and the application of the information contained in this publication.