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FIRE AND SMOKE PROTECTION FEATURES
722.2.2 Concrete floor and roof slabs. Reinforced and For 4t > s > 2t, the thickness to be used shall be
prestressed floors and roofs shall comply with Section 4t
722.2.2.1. Multicourse floors and roofs shall comply with t + ----- – 1 t – e t (Equation 7-5)
Sections 722.2.2.2 and 722.2.2.3, respectively. s
where:
722.2.2.1 Reinforced and prestressed floors and roofs.
The minimum thicknesses of reinforced and prestressed s = Spacing of ribs or undulations.
concrete floor or roof slabs for fire-resistance ratings of t = Minimum thickness.
1 hour to 4 hours are shown in Table 722.2.2.1. = Equivalent thickness of the slab calculated as
t
e
Exception: Minimum thickness shall not be required the net area of the slab divided by the width, in
for floors and ramps within parking garages con- which the maximum thickness used in the
structed in accordance with Sections 406.5 and 406.6. calculation shall not exceed 2t.
TABLE 722.2.2.1
MINIMUM SLAB THICKNESS (inches) 2t t
FIRE-RESISTANCE RATING (hours)
CONCRETE TYPE
1 1 1 / 2 2 3 4
s
Siliceous 3.5 4.3 5 6.2 7
Carbonat 3.2 4 4.6 5.7 6.6 NEGLECT SHADED AREA IN CALCULATION OF EQUIVALENT THICKNESS
Sand-lightweight 2.7 3.3 3.8 4.6 5.4
Lightweight 2.5 3.1 3.6 4.4 5.1 t
For SI: 1 inch = 25.4 mm.
722.2.2.1.1 Hollow-core prestressed slabs. For hol- s
low-core prestressed concrete slabs in which the cores For SI: 1 inch = 25.4 mm.
are of constant cross section throughout the length, FIGURE 722.2.2.1.3
the equivalent thickness shall be permitted to be SLABS WITH RIBBED OR UNDULATING SOFFITS
obtained by dividing the net cross-sectional area of
the slab including grout in the joints, by its width. 722.2.2.2 Multicourse floors. The fire-resistance rat-
ings of floors that consist of a base slab of concrete
722.2.2.1.2 Slabs with sloping soffits. The thickness with a topping (overlay) of a different type of concrete
of slabs with sloping soffits (see Figure 722.2.2.1.2) shall comply with Figure 722.2.2.2.
shall be determined at a distance 2t or 6 inches (152
mm), whichever is less, from the point of minimum CARBONATE BASE SILICEOUS BASE
THICKNESS OF SAND-LIGHTWEIGHT CONCRETE OVERLAY, INCHES 3 2 1hr. 2hr. 3hr. 3 2 1hr. 2hr. 3hr.
thickness, where t is the minimum thickness. 5 5
DETERMINE THICKNESS HERE 4 4
t 4hr. 4hr.
2t OR 6 INCHES, 1 0 1 2 3 4 5 1 0 1 2 3 4 5
WHICHEVER IS LESS THICKNESS OF NORMAL-WEIGHT CONCRETE BASE SLAB, INCHES
For SI: 1 inch = 25.4 mm.
FIGURE 722.2.2.1.2 CARBONATE BASE SILICEOUS BASE
DETERMINATION OF SLAB
THICKNESS FOR SLOPING SOFFITS 5 5
722.2.2.1.3 Slabs with ribbed soffits. The thickness 4 4hr. 4 4hr.
of slabs with ribbed or undulating soffits (see Figure OVERLAY THICKNESS, INCHES 3 2hr. 3hr. 3 3hr.
722.2.2.1.3) shall be determined by one of the fol- 2 1hr. 2 2hr.
lowing expressions, whichever is applicable: 1hr.
For s > 4t, the thickness to be used shall be t 1 1
For s ≤ 2t, the thickness to be used shall be t 0 1 2 3 4 5 0 1 2 3 4 5
e
THICKNESS OF SAND-LIGHTWEIGHT CONCRETE BASE SLAB, INCHES
For SI: 1 inch = 25.4 mm.
FIGURE 722.2.2.2
FIRE-RESISTANCE RATINGS FOR
TWO-COURSE CONCRETE FLOORS
2018 INTERNATIONAL BUILDING CODE ® 185
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