| Fire resistance
ratings can be calculated using a method that multiplies the
percent of solid material in the concrete masonry unit by
the actual thickness (in inches) of the blocks to determine
the hourly rating for the type of aggregate used. Contact
Trenwyth for specific fire ratings.
FIRE RESISTANCE RATINGS/MINIMUM
REQUIRED EQUIVALENT INCHES
Aggregate Type in
The Concrete Masonry Unit |
Fire Resistance |
0.5 Hr. |
0.75 Hr. |
1 Hr. |
1.5 Hr. |
2 Hr. |
3 Hr. |
4 Hr. |
Calcareous or
siliceous gravel |
2.0 in. |
2.4 in. |
2.8 in. |
3.6 in. |
4.2 in. |
5.3 in. |
6.2 in. |
Limestone, cinders
or slag |
1.9 in. |
2.3 in. |
2.7 in. |
3.4 in. |
4.0 in. |
5.0 in. |
5.9 in. |
Expanded clay,
shale or slate |
1.8 in. |
2.2 in. |
2.6 in. |
3.3 in. |
3.6 in. |
4.4 in. |
5.1 in. |
Expanded slag
or pumice |
1.5 in. |
1.9 in. |
2.1 in. |
2.7 in. |
3.2 in. |
4.0 in. |
4.7 in. |
Calculating "Equivalent Thickness"
is simply determining what the block thickness would be if
the same amount of material contained in a hollow unit were
re-molded without core holes.
EQUIVALENT THICKNESS OF CONCRETE
MASONRY UNITS (IN INCHES)
| Nominal
Width
(Inches) |
Equivalent Thickness |
|
Based on Typical
Hollow Units (1) |
Based on Percent
Solid |
| (75%
- semi-solid) |
(100%
- solid) |
| 4 |
2.68
(73.8%) |
2.72 |
3.625 |
| 6 |
3.09
(55.0%) |
4.22 |
5.625 |
| 8 |
4.04
(53.0%) |
5.72 |
7.625 |
| 10 |
4.98 (51.7%) |
7.22 |
9.625 |
| 12 |
5.77 (49.6%) |
8.72 |
11.625 |
CALCULATING ESTIMATED FIRE
RESISTANCE EXAMPLE
An 8" hollow masonry
wall is constructed of expanded slag units reported
to be 53%* solid. What is the estimated fire resistance
of the wall? (modular units)
Equivalent Thickness = % solid
x depth
Example: .53 x 7.625 in. = 4.04 inches
From Table: 3 hr. Fire Resistance
requires 4.0 inches
*Percentage solid can be
calculated from net area or net volume as determined
by ASTM C140 "Methods of Testing Concrete Masonry
Units".
|
(1) Information based on data published by the
National Concrete Masonry Association in NCMA TEK 7-1A, available
at www.trenwyth.com. |
