Page 467 - Forensic Structural Engineering Handbook

MASONRY STRUCTURES 13.13

Fire Resistance
The Code Requirements for Determining Fire Resistance of Concrete and Masonry
30
6
Construction Assemblies provides a method for calculating fire resistance. Grimm provides a
bibliography on masonry fire resistance with 192 citations. Tables 13.6 through 13.10 provide
data on masonry fire resistance. Data in Tables 13.6 and 13.8 are excerpts from Ref. 6.
Thermal Conductivity

Clay Brick Masonry. The author’s estimate for the thermal conductivity of clay brick
masonry is
k ≈ 1.139W 0.2321 eω –76.62
b

TABLE 13.6 Required Minimum Equivalent Thickness for Fire Resistance* of
Concrete Masonry Walls, in (mm)
Fire resistance rating, h
Concrete aggregate 1 1.5 2 3 4

Calcareous or siliceous gravel 2.8 3.6 4.2 5.3 6.2
(other than limestone) (71) (91) (107) (135) (157)
Limestone, cinders, 2.7 3.4 4.0 5.0 5.9
or air-cooled slag (69) (86) (102) (127) (150)
Expanded clay, shale, 2.6 3.3 3.6 4.4 5.1
or slate (66) (84) (91) (123) (130)
Expanded slag or pumice 2.1 2.7 3.2 4.0 4.7
(53) (69) (81) (102) (119)

*Fire resistance ratings between those listed should be determined by linear interpolation based
on the equivalent thickness of the masonry.
Required minimum equivalent thickness corresponding to the fire resistance rating for tests made
with a combination of aggregates should be determined by linear interpolation based on the percent
by volume of each type of aggregate.

TABLE 13.7 Minimum Equivalent Thickness Required by ASTM C 90 for Load-
Bearing Concrete Masonry Units*
Nominal thickness, Specified thickness, Minimum equivalent
in (mm) in (mm) thickness, in (mm)

4 (100) 3.63 (92) 1.91 (49)
6 (150) 5.63 (143) 2.66 (68)
8 (200) 7.63 (194) 3.41 (87)
10 (250) 9.63 (245) 4.16 (106)
12 (300) 11.63 (295) 4.91 (125)

*Some manufacturers produce concrete masonry units having greater equivalent thicknesses
than the minimum requirements of ASTM C 90, Specification for Loadbearing Concrete
Masonry Units. 62