Masonry Magazine October 1993 Page. 26
Clay and Shale Masonry Units
Clay and shale masonry units are manufactured in a number of sizes and shapes. Clay and shale masonry units are classified as either solid units or hollow units. Solid units may contain up to 25 percent void area as a percentage of the gross cross-sectional area of the unit. Hollow units are classified as H40V for units with a total void area greater than 25 percent and less than 40 percent of the gross cross-sectional area, or H60V for units with a total void area greater than 40 percent and less than 60 percent of the gross cross-sectional area. The number and size of voids vary with unit size and manufacturing equipment.
The range of sizes of clay and shale masonry units is given in Table 1. The names given for unit sizes in Table 1 were established by consensus of United States brick manufacturers and are standard terminology for the brick industry. Further information on masonry unit sizes and coursing of brickwork can be found in the Technical Notes 10 Series on estimating brickwork.
One criteria for unit selection may be accommodation of reinforcement within the unit itself. Placement of steel reinforcement within the cores or cells of hollow units or solid cored units is permitted by the MSJC Code and Specifications. A core is a void area less than or equal to 1½ in. (970 mm²). A cell is a void area which is larger than 1½ in. (970 mm²). When placing reinforcement within a unit, adequate space for grouting must be provided. Specifically, MSJC Code Section 8.3.5 requires that the minimum distance between the steel reinforcement and the surrounding masonry unit be ¼ in. (6 mm) when fine grout is used and ½ in. (13 mm) when coarse grout is used.
In certain instances, the cross-sectional area of masonry units may need to be determined. For example, the compressive strength of a masonry prism is determined based on the unit's gross cross-sectional area when the prism is constructed of solid units or fully grouted hollow units, and on the unit's net cross-sectional area when the prism is constructed of hollow units. For solid units which contain cores, the gross cross-sectional area is used as the net cross-sectional area. Unit cross-sectional area may be determined in accordance with ASTM C 67 Methods of Sampling and Testing Brick and Structural Clay Tile.
The shell and web thickness of hollow units may need to be determined because hollow unit brick masonry walls are typically face-shell bedded, while columns, pilasters and the first course of walls must be fully bedded. Minimum thickness requirements for shells and webs of hollow units are established by ASTM C 652 Specification for Hollow Brick (Hollow Masonry Units Made From Clay or Shale). These limits are given in Table 2. Many manufacturers exceed the minimum thickness requirements given in Table 2, so it is advisable to request actual unit dimensions for design purposes.
TABLE 1
BIA Standard Nomenclature for Brick Sizes
| Unit Name | Unit Dimensions |
|---|---|---|
| | Width, in. (mm) | Height, in. (mm) | Length, in. (mm) |
| Modular | 3⅝-3⅝ (89-92) | 2¼ (57) | 7⅝-7⅝ (190-194) |
| Standard | 3⅝-3⅝ (89-92) | 2¼ (57) | 8 (203) |
| Engineer Modular | 3⅝-3⅝ (89-92) | 2¾-2¹³/₁₆ (70-71) | 7⅝-7⅝ (190-194) |
| Engineer Standard | 3⅝-3⅝ (89-92) | 2¾-2¹³/₁₆ (70-71) | 8 (203) |
| Closure Modular | 3⅝-3⅝ (89-92) | 3⅝-3⅝ (89-92) | 7⅝-7⅝ (190-194) |
| Closure Standard | 3⅝-3⅝ (89-92) | 3⅝-3⅝ (89-92) | 8 (203) |
| Roman | 3⅝-3⅝ (89-92) | 1⅝ (41) | 11½-11⅝ (292-295) |
| Norman | 3⅝-3⅝ (89-92) | 2¼ (57) | 11½-11⅝ (292-295) |
| Engineer Norman | 3⅝-3⅝ (89-92) | 2¾-2¹³/₁₆ (70-71) | 11½-11⅝ (292-295) |
| Utility | 3⅝-3⅝ (89-92) | 3⅝-3⅝ (89-92) | 11½-11⅝ (292-295) |
| King Size | 3 (76) | 2⅝-2¾ (67-70) | 9½-9⅝ (241-244) |
| Queen Size | 3 (76) | 2¾ (70) | 7⅝-8 (194-203) |
Steel Reinforcement
Steel reinforcement for brick masonry assemblages consists of bars and wires. Reinforcing bars are placed in grouted cavities, pockets, cores, cells or bond beams of brick masonry walls, columns, pilasters and beams. Steel wire reinforcement is placed in brick masonry mortar joints to reinforce individual assemblages or to tie structural elements together, such as the wythes of a multi-wythe wall. Common bar and wire section properties are given in Table 3. The sizes of reinforcement listed in Table 3 are those permitted by the MSJC Code. The cross-sectional area of reinforcement is used in MSJC Code Eq. 7-10 to determine the spacing of shear reinforcement. The diameter of reinforcement is used to establish placement limits and minimum reinforcement development length requirements given in Chapter 8 of the MSJC Code.
SECTION PROPERTIES OF BRICK MASONRY ASSEMBLAGES
The section properties of the assemblage of the constituent materials, along with the strength of the materials, determine the overall behavior of the brick masonry assemblage.