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The provisions of this section contain procedures by which the fire-resistance ratings of concrete assemblies are established by calculations.
722.2.1 Concrete Walls
Cast-in-place and precast concrete walls shall comply with Section 722.2.1.1. Multiwythe concrete walls shall comply with Section 722.2.1.2. Joints between precast panels shall comply with Section 722.2.1.3. Concrete walls with gypsum wallboard or plaster finish shall comply with Section 722.2.1.4.
722.2.1.1 Cast-in-Place or Precast Walls
The minimum equivalent thicknesses of cast-in-place or precast concrete walls for fire-resistance ratings of 1 hour to 4 hours are shown in Table 722.2.1.1. For solid walls with flat vertical surfaces, the equivalent thickness is the same as the actual thickness. The values in Table 722.2.1.1 apply to plain, reinforced or prestressed concrete walls.
TABLE 722.2.1.1
MINIMUM EQUIVALENT THICKNESS OF CAST-IN-PLACE OR PRECAST CONCRETE WALLS, LOAD-BEARING OR NONLOAD-BEARING
CONCRETE TYPE MINIMUM SLAB THICKNESS (inches) FOR FIRE-RESISTANCE RATING OF
1 hour 11/2 hours 2 hours 3 hours 4 hours
Siliceous 3.5 4.3 5.0 6.2 7.0
Carbonate 3.2 4.0 4.6 5.7 6.6
Sand-lightweight 2.7 3.3 3.8 4.6 5.4
Lightweight 2.5 3.1 3.6 4.4 5.1
For SI: 1 inch = 25.4 mm.
722.2.1.1.1 Hollow-Core Precast Wall Panels
For hollow-core precast concrete wall panels in which the cores are of constant cross section throughout the length, calculation of the equivalent thickness by dividing the net cross-sectional area (the gross cross section minus the area of the cores) of the panel by its width shall be permitted
722.2.1.1.2 Core Spaces Filled
Where all of the core spaces of hollow-core wall panels are filled with loose-fill material, such as expanded shale, clay or slag, or vermiculite or perlite, the fire-resistance rating of the wall is the same as that of a solid wall of the same concrete type and of the same overall thickness.
722.2.1.1.3 Tapered Cross Sections
The thickness of panels with tapered cross sections shall be that determined at a distance 2t or 6 inches (152 mm), whichever is less, from the point of minimum thickness, where t is the minimum thickness.
722.2.1.1.4 Ribbed or Undulating Surfaces
The equivalent thickness of panels with ribbed or undulating surfaces shall be determined by one of the following expressions:
For s ≥ 4t, the thickness to be used shall be t
For s ≤ 2t, the thickness to be used shall be te
For 4t > s > 2t, the thickness to be used shall be
(Equation 7-3)
where:
= Spacing of ribs or undulations.
= Minimum thickness.
t = Equivalent thickness of the panel calculated as the net cross-sectional area of the panel divided by the width, in which the maximum thickness used in the calculation shall not exceed 2t.
722.2.1.2 Multiwythe Walls
For walls that consist of two wythes of different types of concrete, the fire-resistance ratings shall be permitted to be determined from Figure 722.2.1.2.
TABLE 722.2.1.2(1)
VALUES OF Rn0.59 FOR USE IN EQUATION 7-4
TYPE OF MATERIAL THICKNESS OF MATERIAL (inches)
11/2 2 21/2 3 31/2 4 41/2 5 51/2 6 61/2 7
Siliceous aggregate concrete 5.3 6.5 8.1 9.5 11.3 13.0 14.9 16.9 18.8 20.7 22.8 25.1
Carbonate aggregate concrete 5.5 7.1 8.9 10.4 12.0 14.0 16.2 18.1 20.3 21.9 24.7 27.2c
Sand-lightweight concrete 6.5 8.2 10.5 12.8 15.5 18.1 20.7 23.3 26.0c Note c Note c Note c
Lightweight concrete 6.6 8.8 11.2 13.7 16.5 19.1 21.9 24.7 27.8c Note c Note c Note c
Insulating concretea 9.3 13.3 16.6 18.3 23.1 26.5c Note c Note c Note c Note c Note c Note c
Airspaceb
For SI: 1 inch = 25.4 mm, 1 pound per cubic foot = 16.02 kg/m3.
  1. Dry unit weight of 35 pcf or less and consisting of cellular, perlite or vermiculite concrete.
  2. The Rn0.59 value for one 1/2" to 31/2" airspace is 3.3. The Rn0.59 value for two 1/2" to 31/2" airspaces is 6.7.
  3. The fire-resistance rating for this thickness exceeds 4 hours.
Ra, MINUTES R0.59
60 11.20
120 16.85
180 21.41
240 25.37
  1. Based on Equation 7-4.
For SI: 1 inch = 25.4 mm.
FIGURE 722.2.1.2
722.2.1.2.1 Two or More Wythes
The fire-resistance rating for wall panels consisting of two or more wythes shall be permitted to be determined by the formula:
(Equation 7-4)
where:
R = The fire endurance of the assembly, minutes.
R1, R2, and Rn = The fire endurances of the individual wythes, minutes. Values of Rn0.59 for use in Equation 7-4 are given in Table 722.2.1.2(1). Calculated fire-resistance ratings are shown in Table 722.2.1.2(2).
722.2.1.2.2 Foam Plastic Insulation
The fire-resistance ratings of precast concrete wall panels consisting of a layer of foam plastic insulation sandwiched between two wythes of concrete shall be permitted to be determined by use of Equation 7-4. Foam plastic insulation with a total thickness of less than 1 inch (25 mm) shall be disregarded. The Rn value for thickness of foam plastic insulation of 1 inch (25 mm) or greater, for use in the calculation, is 5 minutes; therefore Rn0.59 = 2.5.
722.2.1.3 Joints Between Precast Wall Panels
Joints between precast concrete wall panels that are not insulated as required by this section shall be considered as openings in walls. Uninsulated joints shall be included in determining the percentage of openings permitted by Table 705.8. Where openings are not permitted or are required by this code to be protected, the provisions of this section shall be used to determine the amount of joint insulation required. Insulated joints shall not be considered openings for purposes of determining compliance with the allowable percentage of openings in Table 705.8.
722.2.1.3.1 Ceramic Fiber Joint Protection
Figure 722.2.1.3.1 shows thicknesses of ceramic fiber blankets to be used to insulate joints between precast concrete wall panels for various panel thicknesses and for joint widths of 3/8 inch (9.5 mm) and 1 inch (25 mm) for fire-resistance ratings of 1 hour to 4 hours. For joint widths between 3/8 inch (9.5 mm) and 1 inch (25 mm), the thickness of ceramic fiber blanket is allowed to be determined by direct interpolation. Other tested and labeled materials are acceptable in place of ceramic fiber blankets.


For SI: 1 inch = 25.4 mm.
FIGURE 722.2.1.3.1
CERAMIC FIBER JOINT PROTECTION
722.2.1.4 Walls With Gypsum Wallboard or Plaster Finishes
The fire-resistance rating of cast-in-place or precast concrete walls with finishes of gypsum wallboard or plaster applied to one or both sides shall be permitted to be calculated in accordance with the provisions of this section.
TABLE 722.2.1.4(1)
MULTIPLYING FACTOR FOR FINISHES ON NONFIRE-EXPOSED SIDE OF WALL
TYPE OF FINISH APPLIED TO CONCRETE OR CONCRETE MASONRY WALL TYPE OF AGGREGATE USED IN CONCRETE OR CONCRETE MASONRY
Concrete: siliceous or carbonate concrete masonry: siliceous or carbonate; solid clay brick Concrete: sand-lightweight concrete masonry: clay tile; hollow clay brick; concrete masonry units of expanded shale and < 20% sand Concrete: lightweight concrete masonry: concrete masonry units of expanded shale, expanded clay, expanded slag, or pumice < 20% sand Concrete masonry: concrete masonry units of expanded slag, expanded clay, or pumice
Portland cement-sand plaster 1.00 0.75a 0.75a 0.50a
Gypsum-sand plaster 1.25 1.00 1.00 1.00
Gypsum-vermiculite or perlite plaster 1.75 1.50 1.25 1.25
Gypsum wallboard 3.00 2.25 2.25 2.25
For SI: 1 inch = 25.4 mm.
  1. For Portland cement-sand plaster 5/8 inch or less in thickness and applied directly to the concrete or concrete masonry on the nonfire-exposed side of the wall, the multiplying factor shall be 1.00.
TIME ASSIGNED TO FINISH MATERIALS ON FIRE-EXPOSED SIDE OF WALL
FINISH DESCRIPTION TIME (minutes)
Gypsum wallboard  
3/8 inch
10
1/2 inch
15
5/8 inch
20
2 layers of 3/8 inch
25
1 layer of 3/8 inch, 1 layer of 1/2 inch
35
2 layers of 1/2 inch
40
Type X gypsum wallboard  
1/2 inch
25
5/8 inch
40
Portland cement-sand plaster applied directly to concrete masonry See Note a
Portland cement-sand plaster on metal lath  
3/4 inch
20
7/8 inch
25
1 inch
30
Gypsum sand plaster on 3/8-inch gypsum lath  
1/2 inch
35
5/8 inch
40
3/4 inch
50
Gypsum sand plaster on metal lath  
3/4 inch
50
7/8 inch
60
1 inch
80
For SI: 1 inch = 25.4 mm.
  1. The actual thickness of Portland cement-sand plaster, provided that it is 5/8 inch or less in thickness, shall be permitted to be included in determining the equivalent thickness of the masonry for use in Table 722.3.2.
722.2.1.4.1 Nonfire-Exposed Side
Where the finish of gypsum wallboard or plaster 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 the finish shall first be corrected by multiplying the actual thickness of the finish by the applicable factor determined from Table 722.2.1.4(1) based on the type of aggregate in the concrete. The corrected thickness of finish shall then be added to the actual or equivalent thickness of concrete and fire-resistance rating of the concrete and finish determined from Tables 722.2.1.1 and 722.2.1.2(1) and Figure 722.2.1.2.
722.2.1.4.2 Fire-Exposed Side
Where gypsum wallboard or plaster 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 from Tables 722.2.1.1 and 722.2.1.2(1) and Figure 722.2.1.2 for the concrete alone, or to the rating determined in Section 722.2.1.4.1 for the concrete and finish on the nonfire-exposed side.
722.2.1.4.3 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 Sections 722.2.1.4.1 and 722.2.1.4.2 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.
Exception: For an exterior wall with a fire separation distance greater than 5 feet (1524 mm) the fire shall be assumed to occur on the interior side only.
722.2.1.4.4 Minimum Concrete Fire-Resistance Rating
Where finishes applied to one or both sides of a concrete wall contribute to the fire-resistance rating, the concrete alone shall provide not less than one-half of the total required fire-resistance rating. Additionally, the contribution to the fire resistance of the finish on the nonfire-exposed side of a load-bearing wall shall not exceed one-half the contribution of the concrete alone.
722.2.1.4.5 Concrete Finishes
Finishes on concrete walls that are assumed to contribute to the total fire-resistance rating of the wall shall comply with the installation requirements of Section 722.3.2.5.
722.2.2 Concrete Floor and Roof Slabs
Reinforced and prestressed floors and roofs shall comply with Section 722.2.2.1. Multicourse floors and roofs shall comply with Sections 722.2.2.2 and 722.2.2.3, respectively.
722.2.2.1 Reinforced and Prestressed Floors and Roofs
The minimum thicknesses of reinforced and prestressed concrete floor or roof slabs for fire-resistance ratings of 1 hour to 4 hours are shown in Table 722.2.2.1.
Exception: Minimum thickness shall not be required for floors and ramps within parking garages constructed in accordance with Sections 406.5 and 406.6.
MINIMUM SLAB THICKNESS (inches)
CONCRETE TYPE FIRE-RESISTANCE RATING (hours)
1 11/2 2 3 4
Siliceous 3.5 4.3 5 6.2 7
Carbonate 3.2 4 4.6 5.7 6.6
Sand-lightweight 2.7 3.3 3.8 4.6 5.4
Lightweight 2.5 3.1 3.6 4.4 5.1
For SI: 1 inch = 25.4 mm.
722.2.2.1.1 Hollow-Core Prestressed Slabs
For hollow-core prestressed concrete slabs in which the cores are of constant cross section throughout the length, the equivalent thickness shall be permitted to be obtained by dividing the net cross-sectional area of the slab including grout in the joints, by its width.
722.2.2.1.2 Slabs With Sloping Soffits
The thickness of slabs with sloping soffits (see Figure 722.2.2.1.2) shall be determined at a distance 2t or 6 inches (152 mm), whichever is less, from the point of minimum thickness, where t is the minimum thickness.

For SI: 1 inch = 25.4 mm.
FIGURE 722.2.2.1.2
DETERMINATION OF SLAB THICKNESS FOR SLOPING SOFFITS
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