Structural Concrete - Hassoun

32 Chapter 2 Properties of Reinforced Concrete
Table 2.10
Humidity
Humidity Function for Shrinkage, K h
K h
H ≤ 98% 1 − (H/100) 3
H = 100% −0.2
98% ≤ H ≤ 100% Linear interpolation
Table 2.11
Correction Factor K s
as Function
of Cross-Sectional Shape
Cross-Sectional Shape
K s
Infinite slab 1.00
Infinite cylinder 1.15
Infinite square prism 1.25
Sphere 1.30
Cube 1.55
where
t = age of concrete (days)
t c = age of concrete drying commenced (days)
t − t c = time from end of initial curing
T sh = shrinkage half-time (days) according to Eq. 2.26
E cm28 = modulus of elasticity of concrete at 28 days (MPa or psi)
K s = cross-sectional shape correction factor according to Table 2.11
If type of member is not defined, K s can be assumed to be 1.
Creep Calculation. The creep function, also called creep compliance, J(t, t 0 ) is given by Eq. 2.28:
where
J(t, t 0 )=q 1 + C 0 (t, t 0 )+C d (t, t 0 , t c ) (2.28)
q 1 = instantaneous strain, given in Eq. 2.29
C 0 (t, t 0 ) = compliance function for basic creep composed of three terms, an aging viscoelastic
term, a nonaging viscoelastic term, and an aging flow term given in Eq. 2.30
C d (t, t 0 , t c ) = compliance function for drying creep, given in Eq. 2.38
q 1 = 0.6
(2.29)
E cm28
The compliance function for basic creep, C 0 (t, t 0 ), should be calculated as follows:
( )
C 0 (t, t 0 )=q 2 Q(t, t 0 )+q 3 ln[1 +(t − t 0 ) 0.1 t
]+q 4 ln
(2.30)
t 0
where
q 2 = aging viscoelastic compliance parameter
Q(t, t 0 ) = binomial integral
q 3 = nonaging viscoelastic compliance parameter
q 4 = flow compliance parameter
t 0 = age of concrete at loading (days)