Page 61 - Design of Reinforced Masonry Structures

2.14 CHAPTER TWO

FIGURE 2.10 Weathering index map of the United States. (Courtesy: BIA.)

number of freezing cycle days and the average annual winter rainfall in inches. A freezing
cycle day is defined to occur on any day when the air temperature passes either above or
below 32°F. Brick must meet a grade of SW, MW, or NW based on the weathering index
and the exposure of the brick, and whether the brick is in contact with the earth. Figure 2.10
shows areas of the United States with differing weather conditions. Table 2.5 shows where
each grade is required for face exposure according to ASTM C62-05 [2.12]. It will be
observed that a higher weathering index requires a face brick to meet the SW requirements.
Most manufacturers make bricks to meet the severe weathering (SW) grade so they may
ship brick to all parts of the country. Some manufacturers produce bricks to meet only the
moderate weathering (MW) grade. Brick manufacturers can furnish certification that their
product will meet a certain grade requirement.

TABLE 2.5 Grade Requirements for Face Exposure [2.20]
Weathering index
Exposure Less than 50 50–500 500 and greater
In vertical surfaces:
In contact with earth MW SW SW
Not in contact with earth MW SW SW
In other than vertical surfaces:
In contact with earth SW SW SW
Not in contact with earth MW SW SW