Creep and shrinkage

3.1.4 Creep and shrinkage (1)P Creep and shrinkage of the concrete depend on the ambient humidity, the dimensions of the element and the composition of the concrete. Creep is also influenced by the maturity of the concrete when the load is first applied and depends on the duration and magnitude of the loading. (2) The creep coefficient, ϕ(t,t 0 ) is related to E c , the tangent modulus, which may be taken as 1,05 E cm . Where great accuracy is not required, the value found from Figure 3.1 may be considered as the creep coefficient, provided that the concrete is not subjected to a compressive stress greater than 0,45 f ck (t 0 ) at an age t 0 , the age of concrete at the time of loading. Note: For further information, including the development of creep with time, Annex B may be used. (3) The creep deformation of concrete ε cc (∞,t 0 ) at time t = ∞ for a constant compressive stress σ c applied at the concrete age t 0 , is given by: ε cc (∞,t 0 ) = ϕ (∞,t 0 ). (σ c /E c ) (3.6) (4) When the compressive stress of concrete at an age t 0 exceeds the value 0,45 f ck (t 0 ) then creep non-linearity should be considered. Such a high stress can occur as a result of pretensioning, e.g. in precast concrete members at tendon level. In such cases the non-linear notional creep coefficient should be obtained as follows: ϕ k (∞, t 0 ) = ϕ (∞, t 0 ) exp (1,5 (k σ – 0,45)) (3.7) where: ϕ k (∞, t 0 ) is the non-linear notional creep coefficient, which replaces ϕ (∞, t 0 ) k σ is the stress-strength ratio σ c /f cm (t 0 ), where σ c is the compressive stress and f cm (t 0 ) is the mean concrete compressive strength at the time of loading. a) inside conditions - RH = 50% 0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 100 50 30 1 2 3 5 10 20 t 0 ϕ (∞, t 0) S N R 100 300 500 700 900 1100 1300 1500 C20/25 C25/30 C30/37 C35/45 C40/50 C45/55 C50/60 C55/67 C60/75 C70/85 C90/105 C80/95 h 0 (mm)

Creep and shrinkage

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concrete creep

shrinkage

modulus

creep coefficient