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722.3 Concrete Masonry
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(Equation 7-6)
(Equation 7-7)
The provisions of this section contain procedures by which the fire-resistance ratings of concrete masonry are established by calculations.
The equivalent thickness of concrete masonry assemblies, Tea, shall be computed as the sum of the equivalent thickness of the concrete masonry unit, Te, as determined by Section 722.3.1.2, 722.3.1.3 or 722.3.1.4, plus the equivalent thickness of finishes, Tef, determined in accordance with Section 722.3.2:
(Equation 7-6)Te shall be the value obtained for the concrete masonry unit determined in accordance with ASTM C140.
The equivalent thickness, Te, of solid grouted concrete masonry units is the actual thickness of the unit.
The equivalent thickness of completely filled hollow concrete masonry is the actual thickness of the unit where loose-fill materials are: sand, pea gravel, crushed stone, or slag that meet ASTM C33 requirements; pumice, scoria, expanded shale, expanded clay, expanded slate, expanded slag, expanded fly ash, or cinders that comply with ASTM C331; or perlite or vermiculite meeting the requirements of ASTM C549 and ASTM C516, respectively.
The fire-resistance rating of walls and partitions constructed of concrete masonry units shall be determined from Table 722.3.2. The rating shall be based on the equivalent thickness of the masonry and type of aggregate used.
| TYPE OF AGGREGATE | FIRE-RESISTANCE RATING (hours) | ||||||||||||||
| 1/2 | 3/4 | 1 | 11/4 | 11/2 | 13/4 | 2 | 21/4 | 21/2 | 23/4 | 3 | 31/4 | 31/2 | 33/4 | 4 | |
| Pumice or expanded slag | 1.5 | 1.9 | 2.1 | 2.5 | 2.7 | 3.0 | 3.2 | 3.4 | 3.6 | 3.8 | 4.0 | 4.2 | 4.4 | 4.5 | 4.7 |
| Expanded shale, clay or slate | 1.8 | 2.2 | 2.6 | 2.9 | 3.3 | 3.4 | 3.6 | 3.8 | 4.0 | 4.2 | 4.4 | 4.6 | 4.8 | 4.9 | 5.1 |
| Limestone, cinders or unexpanded slag | 1.9 | 2.3 | 2.7 | 3.1 | 3.4 | 3.7 | 4.0 | 4.3 | 4.5 | 4.8 | 5.0 | 5.2 | 5.5 | 5.7 | 5.9 |
| Calcareous or siliceous gravel | 2.0 | 2.4 | 2.8 | 3.2 | 3.6 | 3.9 | 4.2 | 4.5 | 4.8 | 5.0 | 5.3 | 5.5 | 5.8 | 6.0 | 6.2 |
For SI: 1 inch = 25.4 mm.
- Values between those shown in the table can be determined by direct interpolation.
- Where combustible members are framed into the wall, the thickness of solid material between the end of each member and the opposite face of the wall, or between members set in from opposite sides, shall be not less than 93 percent of the thickness shown in the table.
- Requirements of ASTM C55, ASTM C73, ASTM C90 or ASTM C744 shall apply.
- Minimum required equivalent thickness corresponding to the hourly fire-resistance rating for units with a combination of aggregate shall be determined by linear interpolation based on the percent by volume of each aggregate used in manufacture.
Where plaster or gypsum wallboard is applied to the side of the wall not exposed to fire, the contribution of the finish to the total fire-resistance rating shall be determined as follows: The thickness of gypsum wallboard or plaster shall be corrected by multiplying the actual thickness of the finish by applicable factor determined from Table 722.2.1.4(1). This corrected thickness of finish shall be added to the equivalent thickness of masonry and the fire-resistance rating of the masonry and finish determined from Table 722.3.2.
Where plaster or gypsum wallboard is applied to the fire-exposed side of the wall, the contribution of the finish to the total fire-resistance rating shall be determined as follows: The time assigned to the finish as established by Table 722.2.1.4(2) shall be added to the fire-resistance rating determined in Section 722.3.2 for the masonry alone, or in Section 722.3.2.1 for the masonry and finish on the nonfire-exposed side.
For a wall without finish on one side or having different types or thicknesses of finish on each side, the calculation procedures of this section shall be performed twice, assuming either side of the wall to be the fire-exposed side. The fire-resistance rating of the wall shall not exceed the lower of the two values calculated.
Exception: For exterior walls with a fire separation distance greater than 5 feet (1524 mm), the fire shall be assumed to occur on the interior side only.
Where the finish applied to a concrete masonry wall contributes to its fire-resistance rating, the masonry alone shall provide not less than one-half the total required fire-resistance rating.
Installation of finishes shall be as follows:
- Gypsum wallboard and gypsum lath applied to concrete masonry or concrete walls shall be secured to wood or steel furring members spaced not more than 16 inches (406 mm) on center (o.c.).
- Gypsum wallboard shall be installed with the long dimension parallel to the furring members and shall have all joints finished.
- Other aspects of the installation of finishes shall comply with the applicable provisions of Chapters 7 and 25.
The fire-resistance rating of wall assemblies constructed of multiple wythes of masonry materials shall be permitted to be based on the fire-resistance rating period of each wythe and the continuous airspace between each wythe in accordance with the following formula:
(Equation 7-7)where:
RA = Fire-resistance rating of the assembly (hours).
R1, R2, ..., Rn = Fire-resistance rating of wythes for 1, 2, n (hours), respectively.
A1, A2, ...., An = 0.30, factor for each continuous airspace for 1, 2, ...n, respectively, having a depth of 1/2 inch (12.7 mm) or more between wythes.
Fire-resistance ratings for concrete masonry lintels shall be determined based on the nominal thickness of the lintel and the minimum thickness of concrete masonry or concrete, or any combination thereof, covering the main reinforcing bars, as determined in accordance with Table 722.3.4, or by approved alternate methods.
| NOMINAL WIDTH OF LINTEL (inches) |
FIRE-RESISTANCE RATING (hours) | |||
| 1 | 2 | 3 | 4 | |
| 6 | 11/2 | 2 | — | — |
| 8 | 11/2 | 11/2 | 13/4 | 3 |
| 10 or greater | 11/2 | 11/2 | 11/2 | 13/4 |
For SI: 1 inch = 25.4 mm.
The fire-resistance rating of concrete masonry columns shall be determined based on the least plan dimension of the column in accordance with Table 722.3.5 or by approved alternate methods.
| FIRE-RESISTANCE RATING (hours) | |||
| 1 | 2 | 3 | 4 |
| 8 inches | 10 inches | 12 inches | 14 inches |
For SI: 1 inch = 25.4 mm.
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