Page 459 - Forensic Structural Engineering Handbook

13.8 MATERIAL-SPECIFIC FORENSIC ANALYSES

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2
mean flexural tensile strength of 76 lb/in with a standard deviation of about 12 lb/in . Strength
is reduced 21 percent with use of type N mortar. High air content associated with use of
masonry cement or air-entrained portland cement–lime mortars reduces flexural strength
about 50 percent. Strength is increased by 105 percent by use of solid units instead of hol-
low units for out-of-plane flexures normal to bed joints. Strength is more than doubled
when bending stress acts parallel rather than perpendicular to bed joints. Deflection at flex-
ural cracking is about 0.036 percent of wall span.
Concrete Masonry in Shear. Mean shear stress at first crack in concrete masonry is about
64 percent of ultimate compressive strength with a coefficient of variation of 25 percent.

Grout Compressive Strength
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Compressive strength of fine grout f (lb/in ) may be estimated as f = 45.23R –1.596 , where
f
f
R = volumetric ratio of aggregate to cement, which is dimensionless. The compressive
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strength of course grout f (lb/in ) may be estimated as f = 54.6R –1.425 . The modulus of elas-
c
c
ticity of grout may be assumed to be 500 times the compressive strength of grout.
Stone Properties
Properties of granite, limestone, and sandstone are given in Table 13.3. Properties of marble
and slate are given in Table 13.4.
Wall Section Properties
Section properties depend on conformance of materials to specifications. Load-bearing
and non-load-bearing masonry units have different dimensional proper ties, as illustrated
in Fig. 13.1.
Reference 37 provides equations and tabular values for the mechanical properties, such
as bed area, moment of inertia, and section modulus, for single-wythe walls of clay or con-
crete masonry in thickness of 4, 6, 8, 10, or 12 in (100, 150, 200, 250, or 300 mm).
A sketch of a composite wall is shown in Fig. 13.2. The mechanical properties of a trans-
formed composite section are functions of each material’s modular ratio n. For a given material
the modular ratio is the quotient of the elastic modulus of the solid material divided by the elas-
tic modulus of the hollow masonry. Reference 37 gives the wall bed areas, moments of inertia,
and section moduli for both sides of composite walls having modular ratios of 0.25, 0.5, 1, 1.5,
2, 2.5, and 3 for walls having a specified 3-in (75-mm) or 4-in (100-mm) solid masonry wythe
and a 4-, 6-, 8-, 10-, or 12-in (100-, 150-, 200-, 250-, or 300-mm) wythe of hollow masonry.

ARCHITECTURAL ENGINEERING PROPERTIES

This section provides information on sound transmission and absorption, fire resistance,
and transmission of heat, air, and vapor.

Acoustical Properties
The sound transmission class (STC) of clay and concrete masonry may be estimated as STC =
0.18W + 39, where W is wall weight in pounds per square foot (see Tables 13.1 and 13.2).
Table 13.5 provides data on sound absorption of masonry. Figure 13.3 illustrates potential
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sound leaks. Grimm discusses the acoustical properties of masonry walls.