722.5.1.4.5 Masonry protection.
BC § 722.5.1.4.5
The fire resistance of structural steel columns protected with concrete masonry units or clay masonry units as illustrated in Figure 722.5.1(7), shall be permitted to be determined from the following expression: R = 0.17 (W/D) 0.7 + [0.285 (T e1.6 /K 0.2 )][1.0 + 42.7 {(A s /d m T e )/(0.25p + T e )} 0.8 ] (Equation 7-16) where: R = Fire-resistance rating of column assembly (hours). W = Average weight of steel column (pounds per foot). D = Heated perimeter of the steel column (inches) (see Figure 722.5.1(7)). T e = Equivalent thickness of concrete or clay masonry unit (inches) (see Table 722.3.2 Note a or Section 722.4.1). K = Thermal conductivity of concrete or clay masonry unit (Btu/hr ft °F) (see Table 722.5.1(3)). A s = Cross-sectional area of steel column (square inches). d m = Density of the concrete or clay masonry unit (pounds per cubic foot). p = Inner perimeter of concrete or clay masonry protection (inches) (see Figure 722.5.1(7)).
