Structural Concrete - Hassoun

44 Chapter 2 Properties of Reinforced Concrete
where
S = coefficient that depends on type of cement and compressive strength
= 0.20 for f cm ≤ 60 MPa (8700 psi) and rapidly hardening high-strength cement (Type III)
= 0.25 for f cm ≤ 60 MPa (8700 psi) and normal and rapidly hardening cement (Type I)
= 0.38 for f cm ≤ 60 MPa (8700 psi) and slow-hardening cement (Type II)
= 0.20 for f cm > 60 MPa (8700 psi) and all types of cement
where
The creep coefficient, φ(t, t 0 ), may be found using the following expression:
φ(t, t 0 )=φ bc (t, t 0 )+φ dc (t, t 0 ) (2.96)
φ bc (t,t 0 ) = basic creep coefficient found from Equation 2.97
φ dc (t,t 0 ) = drying creep coefficient found from Equation 2.101
The basic creep coefficient, φ bc (t, t 0 ), can be found from the following expression:
φ bc (t, t 0 )=β bc (f cm )β bc (t, t 0 ) (2.97)
with
⎧ 58.6
⎪( )
⎪ 0.7
(in.−lb)
fcm
β bc (f cm )= ⎨
⎪ 1.8
(SI)
⎪(f ⎩ cm ) 0.7
[ ( ) 2
30
β bc (t, t 0 )=ln + 0.035 (t − t
t 0 )+1]
0,adj
(2.98)
(2.99)
where
where
t 0,adj = modified age of loading accounting for the effect of creep due to the type of cement according
to Equation 2.100.
[
] α
9
t 0,adj = t 0,T
2 + t + 1 ≥ 0.5 days (2.100)
1.2 0,T
t 0, T = age of concrete at loading adjusted according to the concrete temperature;
for T = 20 ∘ C, t 0, T corresponds to t 0
α = coefficient, which depends on the type of cement
=−1 for slowly hardening or Type II cement
= 0 for normal or rapidly hardening or Type I cement
= 1 for rapidly hardening high-strength or Type III cement
The drying creep coefficient, φ dc (t, t 0 ), may be calculated using the expression:
φ dc (t, t 0 )=β dc (f cm ) ⋅ β(RH) ⋅ β dc (t 0 ) ⋅ β dc (t, t 0 ) (2.101)