Page 129 - Design of Reinforced Masonry Structures

MATERIALS OF MASONRY CONSTRUCTION 3.23

The values of modulus of elasticity of both concrete and clay masonry as a function of
compressive strength of masonry are listed in Table A.14. Also listed in Table A.14 are the
values of the modular ratio (n) defined as the ratio of modulus of elasticity of steel to that
of masonry as given by Eq. (3.4):

n = modulus of elasticity of steel = E s (3.4)
modulus of elastticity of masonry E
m
The shear modulus of masonry (E ) is given by Eq. (3.5):
v
E = 0.4E (3.5)
m
v
3.7.3 Modulus of Elasticity of Grout
The modulus of elasticity of grout, E , is given by Eq. (3.6):
g
E = 500 f ′ (3.6)
g g
where f ′ = 28-day compressive strength of grout.
g
3.8 THERMAL EFFECTS ON MASONRY

All materials are inherently sensitive to fluctuations in temperature. Construction of struc-
ture usually takes place under normal temperature conditions. However, ambient temper-
atures may vary widely, cyclically, between summer and winter, by as much as 100°F
between the two extremes. As a result of temperature changes, most materials expand
(when the temperature rises above normal) and contract (when the temperature falls below
normal). These thermal characteristics are described by a property called coefficient of
thermal expansion. Table 3.9 lists coefficients of thermal expansion for some of the com-
mon building materials.
Masonry responds to temperature variations just like most other materials—expansion
and contraction. The Code ([3.2] Sec 1.8.3) specifies the coefficient of thermal expansion,
k , for clay and concrete masonry as follows:
t
−6
Clay masonry: k = 4 × 10 in./in./°F (3.7)
t
−6
Concrete masonry: k = 4.5 × 10 in./in./°F (3.8)
t
The coefficient of thermal expansion for concrete varies with the type of aggregate [3.46].
TABLE 3.9 Coefficients of Thermal Expansion of Some Common

Building Materials*
Coefficient of thermal expansion
−6
Building material (× 10 in./in./°F)
Clay, shale, or brick masonry 3.6
Normal-weight concrete masonry 5.2
Lightweight concrete masonry 4.3
Normal weight concrete 5.5–7.5
Structural steel 6.6
*Values of coefficients of thermal expansion in metric units (mm/mm/°C) can be
obtained by multiplying the tabulated values by 1.8.