Page 60 - Design of Reinforced Masonry Structures

MASONRY UNITS: APPLICATIONS, TYPES, SIZES, AND CLASSIFICATION 2.13

and ordering bricks, it is common practice to list the brick dimensions in the standard order
of width, height, and length.
Three different sets of dimensions should be recognized when specifying or designing
with brick: nominal dimensions, specified dimensions, and actual dimensions. Nominal
dimensions are used most often by the architects to plan modular construction so that
all dimensions of the brick and the elements of buildings appear as multiples of a given
module.
The nominal dimension for brick masonry equals the specified dimension plus one
intended mortar joint thickness, which is the thickness required so that the thickness of the
unit and the joint thickness together match the coursing module. Nominal brick dimensions
are based on multiples (or fractions) of 4 in. Specified dimensions are shown in Tables 2.2
and 2.3. Details of modular construction can be found in Ref. [2.11].
Specified dimension is defined as the anticipated manufactured dimension. They are
typically ⁄ 8 to ⁄ 2 in. smaller than the nominal dimensions, based on the joint thicknesses
3
1
3
1
of ⁄ 8 and ⁄ 2 in., respectively. The specified dimensions are used by engineers for structural
design purposes. Therefore, these dimensions should be stated in the project specifications
and purchase orders. See Tables 2.2 and 2.3 for details.
The actual dimension is the dimension of the unit as manufactured. Actual dimensions
of a brick unit may vary slightly from the specified dimensions; however, the variations
must be within the range of acceptable tolerances. Dimensional tolerances are defined by
ASTM C216-05a: Specifications for Hollow Brick (Hollow Masonry Units Made from
Clay or Shale) [2.14].
Although nominal dimensions are given only for the modular bricks, the heights for
modular and nonmodular brick units are the same, that is, all bricks are modular in height.
See Tables 2.2 and 2.3. This is because when modular bricks were first introduced, they
were faced with the problem of supplying bricks to match the existing nonmodular con-
struction, an important criterion for preserving the architectural and aesthetic characteris-
tics of a project.

2.4.6 Durability Grades
Durability of material used in engineering construction is an important consideration. For
this purpose, bricks are specified by the durability grades according to ASTM C652-01a
[2.15] as follows:
1. SW (Severe weathering): These bricks are to be used where a high degree of resistance
to disintegrating weathering and frost action is required while saturated with water.
They also provide higher compressive strength than that of other category bricks.
2. MW (Moderate weathering): These bricks are to be used where only moderate degree
of resistance to weathering action is required, and where frost action is not very likely.

They are intended for applications that are unlikely to be saturated with water when
exposed to freezing temperatures.
Reference [2.30] provides an additional durability classification:
3. NW (No weathering): Bricks intended for use as backup or interior masonry; or if
exposed, for use where no frost action occurs; or if frost action occurs, where the annual
precipitation is less than 20 in. The reason for these restrictions is that these bricks
would disintegrate rapidly when subjected to freeze-thaw cycles.
The selection of specific grade of brick for face exposure of vertical or horizontal sur-
faces is related to weathering index which is defined as the product of the average annual