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FIRE AND SMOKE PROTECTION FEATURES

D = Heated perimeter of the structural steel column L= Interior dimension of one side of a square
(inches). concrete box protection (inches).
C and C = Material-dependent constants. 722.5.1.4.1 Reentrant space filled. For wide-flange
2
1
W = Weight of structural steel columns (pounds per structural steel columns completely encased in con-
linear foot). crete with all reentrant spaces filled [Figure
The fire resistance of structural steel columns pro- 722.5.1(6)(c)], the thermal capacity of the concrete
within the reentrant spaces shall be permitted to be
tected with intumescent or mastic fire-resistant coatings added to the thermal capacity of the steel column, as
shall be determined on the basis of fire-resistance tests follows:
in accordance with Section 703.2.
722.5.1.3.1 Material-dependent constants. The H = 0.11 W + (p c /144) (b d - A )
s
f
c c
material-dependent constants, C and C , shall be (Equation 7-15)
2
1
determined for specific fire-resistant materials on the where:
basis of standard fire endurance tests in accordance b = Flange width of the structural steel column
with Section 703.2. Unless evidence is submitted to f (inches).
the building official substantiating a broader applica- d= Depth of the structural steel column (inches).
tion, this expression shall be limited to determining
the fire resistance of structural steel columns with A = Cross-sectional area of the steel column
s
weight-to-heated-perimeter ratios (W/D) between the (square inches).
largest and smallest columns for which standard fire- 722.5.1.4.2 Concrete properties unknown. If spe-
resistance test results are available. cific data on the properties of concrete are not avail-
722.5.1.3.2 Identification. Sprayed fire-resistant able, the values given in Table 722.5.1(2) are
materials shall be identified by density and thickness permitted.
required for a given fire-resistance rating. 722.5.1.4.3 Minimum concrete cover. For struc-
tural steel column encased in concrete with all
722.5.1.4 Concrete-protected columns. The fire resis-
tance of structural steel columns protected with con- reentrant spaces filled, Figure 722.5.1(6)(c) and
crete, as illustrated in Figure 722.5.1(6)(a) and (b), Tables 722.5.1(7) and 722.5.1(8) indicate the thick-
shall be permitted to be determined from the following ness of concrete cover required for various fire-
expression: resistance ratings for typical wide-flange sections.
The thicknesses of concrete indicated in these
R = R (1 + 0.03m) (Equation 7-14) tables apply to structural steel columns larger than
o
where: those listed.
1.6
0.7
R = 10 (W/D) + 17 (h /k c 0.2 ) × 722.5.1.4.4 Minimum precast concrete cover. For
o
0.8
[1 + 26 {H/p c h (L + h)} ] structural steel columns protected with precast con-
c c
As used in these expressions: crete column covers as shown in Figure
R= enduran at equilibr moisture 722.5.1(6)(a), Tables 722.5.1(9) and 722.5.1(10)
indicate the thickness of the column covers required
conditions (minutes). for various fire-resistance ratings for typical wide-
R = Fire endurance at zero moisture content flange shapes. The thicknesses of concrete given in
o
(minutes). these tables apply to structural steel columns larger
m= Equilibrium moisture content of the concrete by than those listed.
volume (percent). 722.5.1.4.5 Masonry protection. The fire resis-
W= Average weight of the structural steel column tance of structural steel columns protected with con-
(pounds per linear foot). crete masonry units or clay masonry units as
D= Heated perimeter of the structural steel column illustrated in Figure 722.5.1(7) shall be permitted to
(inches). be determined from the following expression:
0.2
0.7
h= Thickness of the concrete cover (inches). R = 0.17 (W/D) + [0.285 (T e 1.6 /K )]
0.8
k = Ambient temperature thermal conductivity of the [1.0 + 42.7 {(A /d T )/(0.25p + T )} ]
c s m e e
concrete (Btu/hr ft °F). (Equation 7-16)
H= Ambient temperature thermal capacity of the where:
steel column = 0.11W (Btu/ ft °F). R = Fire-resistance rating of column assembly
p = Concrete density (pounds per cubic foot).
c (hours).
c = Ambient temperature specific heat of concrete
c W= Average weight of structural steel column
(Btu/lb °F). (pounds per foot).

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