CONCRETE

Creep Coefficient of Concrete (θ)

Ratio of creep strain to elastic strain under sustained load — per IS 456 Cl. 6.2.5.1 — depends on age at loading and humidity.

Also calledcreep coefficientcreep concretecreep strainis 456 creeplong-term deformation

Related on InfraLens

CODES

IS 456

Definition

Creep coefficient θ per IS 456 Cl. 6.2.5.1: θ_28 = 1.6 (loaded at 28 days); θ_7 = 2.2 (loaded at 7 days); θ_1y = 1.1 (loaded at 1 year). Used in long-term deflection: Ec,long = Ec / (1 + θ). Creep is the time-dependent strain under constant stress — concrete deforms slowly over months/years.

Typical values

Age at loading = 7 daysθ = 2.2

Age at loading = 28 daysθ = 1.6

Age at loading = 1 yearθ = 1.1

Typical long-term Ec reduction1 / (1+θ) ≈ 0.38

Where used

Long-term deflection check
Prestress loss calculation
Composite-section analysis
Differential settlement assessment

Acceptance / threshold

Per IS 456 Cl. 6.2.5.1 — apply creep coefficient based on actual age at loading; reduce Ec accordingly for sustained-load deflection.

Site example

Slab loaded at 28 days (θ=1.6): long-term elastic deflection multiplier = (1 + 1.6) = 2.6× short-term. Deflection that's 8 mm immediately becomes ~21 mm after years.

Frequently asked

What is creep coefficient θ?

θ is the ratio of creep strain to elastic strain. Per IS 456 Cl. 6.2.5.1: 2.2 at 7 days, 1.6 at 28 days, 1.1 at 1 year. Drives long-term deflection.

Related terms

Creep & Shrinkage (Concrete)

Time-dependent deformation of concrete under sustained load

Modulus of Elasticity of Concrete (Ec)

Short-term static modulus of elasticity of concrete per IS 456 Cl. 6.2.3.1 — Ec = 5000√fck (in N/mm² with fck in N/mm²).

Formwork Stripping Time (Removal Schedule)

Minimum time before formwork can be safely removed per IS 456 Cl. 11.3 — depends on member type, climate, and concrete strength.

Shrinkage Strain of Concrete (εcs)

Volumetric strain of concrete due to drying and chemical shrinkage — per IS 456 Cl. 6.2.4.1 — typical value 0.0003 (300 microstrain).