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The fire-resistance rating of masonry walls shall be based on the equivalent thickness as calculated in accordance with this section. The calculation shall take into account finishes applied to the wall and airspaces between wythes in multiwythe construction.
TABLE 722.4.1(1)
FIRE-RESISTANCE PERIODS OF CLAY MASONRY WALLS
MATERIAL TYPE MINIMUM REQUIRED EQUIVALENT THICKNESS FOR FIRE RESISTANCEa, b, c (inches)
1 hour 2 hours 3 hours 4 hours
Solid brick of clay or shaled 2.7 3.8 4.9 6.0
Hollow brick or tile of clay or shale, unfilled 2.3 3.4 4.3 5.0
Hollow brick or tile of clay or shale, grouted or filled with materials specified in Section 722.4.1.1.3 3.0 4.4 5.5 6.6
For SI: 1 inch = 25.4 mm.
  1. Equivalent thickness as determined from Section 722.4.1.1.
  2. Calculated fire resistance between the hourly increments specified shall be determined by linear interpolation.
  3. Where combustible members are framed in 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.
  4. For units in which the net cross-sectional area of cored brick in any plane parallel to the surface containing the cores is not less than 75 percent of the gross cross-sectional area measured in the same plane.
FIRE-RESISTANCE RATINGS FOR BEARING STEEL FRAME BRICK VENEER WALLS OR PARTITIONS
WALL OR PARTITION ASSEMBLY PLASTER SIDE EXPOSED (hours) BRICK FACED SIDE EXPOSED (hours)
Outside facing of steel studs: 1/2" wood fiberboard sheathing next to studs, 3/4" airspace formed with 3/4" × 15/8" wood strips placed over the fiberboard and secured to the studs; metal or wire lath nailed to such strips, 33/4" brick veneer held in place by filling 3/4" airspace between the brick and lath with mortar.

Inside facing of studs: 3/4" unsanded gypsum plaster on metal or wire lath attached to 5/16" wood strips secured to edges of the studs.
1.5 4
Outside facing of steel studs: 1" insulation board sheathing attached to studs, 1" airspace, and 33/4" brick veneer attached to steel frame with metal ties every 5th course.

Inside facing of studs: 7/8" sanded gypsum plaster (1:2 mix) applied on metal or wire lath attached directly to the studs.
1.5 4
Same as previous assembly except use 7/8" vermiculite-gypsum plaster or 1" sanded gypsum plaster (1:2 mix) applied to metal or wire. 2 4
Outside facing of steel studs: 1/2" gypsum sheathing board, attached to studs, and 33/4" brick veneer attached to steel frame with metal ties every 5th course.

Inside facing of studs: 1/2" sanded gypsum plaster (1:2 mix) applied to 1/2" perforated gypsum lath securely attached to studs and having strips of metal lath 3 inches wide applied to all horizontal joints of gypsum lath.
2 4
For SI: 1 inch = 25.4 mm.

TABLE 722.4.1(3)
VALUES OF Rn0.59
Rn 0.59 R (hours)
1 1.0
2 1.50
3 1.91
4 2.27
 
TABLE 722.4.1(4)
COEFFICIENTS FOR PLASTER, pl a
THICKNESS OF PLASTER (inch) ONE SIDE TWO SIDES
1/2 0.3 0.6
5/8 0.37 0.75
3/4 0.45 0.90
For SI: 1 inch = 25.4 mm.
  1. Values specified in the table are for 1:3 sanded gypsum plaster.
NOMINAL LINTEL WIDTH (inches) MINIMUM LONGITUDINAL REINFORCEMENT COVER FOR FIRE RESISTANCE (inches)
1 hour 2 hours 3 hours 4 hours
6 11/2 2 NP NP
8 11/2 11/2 13/4 3
10 or more 11/2 11/2 11/2 13/4
For SI: 1 inch = 25.4 mm.
NP = Not Permitted.

TABLE 722.4.1(6)
REINFORCED CLAY MASONRY COLUMNS
COLUMN SIZE FIRE-RESISTANCE RATING (hours)
1 2 3 4
Minimum column dimension (inches) 8 10 12 14
For SI: 1 inch = 25.4 mm.
722.4.1.1 Equivalent Thickness
The fire-resistance ratings of walls or partitions constructed of solid or hollow clay masonry units shall be determined from Table 722.4.1(1) or Table 722.4.1(2). The equivalent thickness of the clay masonry unit shall be determined by Equation 7-8 where using Table 722.4.1(1). The fire-resistance rating determined from Table 722.4.1(1) shall be permitted to be used in the calculated fire-resistance rating procedure in Section 722.4.2.
(Equation 7-8)
where:
Te = The equivalent thickness of the clay masonry unit (inches).
Vn = The net volume of the clay masonry unit (inch3).
L = The specified length of the clay masonry unit (inches).
= The specified height of the clay masonry unit (inches).
722.4.1.1.1 Hollow Clay Units
The equivalent thickness, Te, shall be the value obtained for hollow clay units as determined in accordance with Equation 7-8. The net volume, Vn, of the units shall be determined using the gross volume and percentage of void area determined in accordance with ASTM C67.
722.4.1.1.2 Solid Grouted Clay Units
The equivalent thickness of solid grouted clay masonry units shall be taken as the actual thickness of the units.
722.4.1.1.3 Units With Filled Cores
The equivalent thickness of the hollow clay masonry units is the actual thickness of the unit where completely filled with loose-fill materials of: 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 in compliance with ASTM C331; or perlite or vermiculite meeting the requirements of ASTM C549 and ASTM C516, respectively.
722.4.1.2 Plaster Finishes
Where plaster is applied to the wall, the total fire-resistance rating shall be determined by the formula:
(Equation 7-9)

where:
R  = The fire-resistance rating of the assembly (hours).
Rn  = The fire-resistance rating of the individual wall (hours).
pl = Coefficient for thickness of plaster.
Values for Rn0.59 for use in Equation 7-9 are given in Table 722.4.1(3). Coefficients for thickness of plaster shall be selected from Table 722.4.1(4) based on the actual thickness of plaster applied to the wall or partition and whether one or two sides of the wall are plastered.
722.4.1.3 Multiwythe Walls With Airspace
Where a continuous airspace separates multiple wythes of the wall or partition, the total fire-resistance rating shall be determined by the formula:
(Equation 7-10)
where:
R = The fire-resistance rating of the assembly (hours).
R1, R2 and R = The fire-resistance rating of the individual wythes (hours).
as = Coefficient for continuous airspace.
Values for Rn0.59 for use in Equation 7-10 are given in Table 722.4.1(3). The coefficient for each continuous airspace of 1/2 inch to 31/2 inches (12.7 to 89 mm) separating two individual wythes shall be 0.3.
722.4.1.4 Nonsymmetrical Assemblies
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 to be the fire-exposed side of the wall. The fire resistance of the wall shall not exceed the lower of the two values determined.
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.

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