Instantly calculate concrete creep coefficient, creep strain, elastic strain, and total deformation for any structural concrete member using the ACI 209R-92 model — with humidity, loading age, and V/S ratio corrections.
Enter your concrete properties and loading conditions to calculate creep coefficient, creep strain & total deformation.
Normal range: 3,000–10,000 PSI (ACI 209.2R-08 applicable range)
Typically 30–45% of f'c for service load conditions
Min. 7 days moist cured (Type I/II) · Later loading = less creep
Time elapsed since load was applied (t − t₀)
40% = very dry · 70% = standard · 100% = submerged
Slab ~2 in · Beam ~3–4 in · Column ~4–6 in · Wall ~3 in
Enter for total deformation calculation (leave blank to skip)
Concrete creep is the time-dependent increase in strain (deformation) that occurs in a concrete member subjected to a sustained constant stress — even when no additional load is applied. Unlike elastic deformation which is instantaneous, creep develops gradually over months and years, primarily driven by the viscous flow and moisture migration within the calcium silicate hydrate (C-S-H) gel of the cement paste. In structural engineering, accurately predicting creep strain is essential for calculating long-term deflections in beams, prestress losses in post-tensioned members, column shortening in high-rise buildings, and time-dependent stress redistribution in statically indeterminate structures.
Creep is load-induced and only occurs in members carrying sustained stress. Shrinkage is load-independent — it occurs in all exposed concrete as moisture evaporates from the cement paste. Both contribute to the total time-dependent strain of a concrete member and are predicted separately in ACI 209.2R-08. This calculator covers creep strain only (basic creep + drying creep combined).
In high-rise buildings, concrete columns under sustained axial load can shorten by 1–3 inches over 5–10 years due to creep and shrinkage. This differential shortening between concrete columns and steel cores requires careful engineering analysis per ACI 209R-92.
In prestressed and post-tensioned concrete (bridges, parking structures), creep causes progressive loss of prestress force — typically 5–8% for creep alone. AASHTO LRFD Article 5.9.5.4 governs prestress loss calculations in US bridge design.
ACI 318-19 Section 24.2.4 requires that long-term deflections of flexural members be estimated by multiplying the immediate deflection by (1 + λΔ), where λΔ incorporates the creep and shrinkage multiplier — typically 1.0–2.0 depending on compression reinforcement ratio.
The ACI 209R-92 model is the most commonly used creep prediction method in the USA for non-bridge structural concrete. It calculates a time-dependent creep coefficient φ(t,t₀) — the ratio of creep strain to initial elastic strain — using a hyperbolic time function multiplied by an ultimate creep coefficient corrected for ambient humidity, loading age, and member geometry. For highway bridges, the AASHTO LRFD creep model (Article 5.4.2.3.2) is the governing standard instead.
The ACI 209R-92 model is calibrated for normal-weight concrete with f'c between 3,000–10,000 PSI, moist cured for at least 1 day, and loaded after curing. Accuracy is ±20–30% under standard conditions. For high-strength concrete (HSC > 8,000 PSI), high-performance concrete, or structures sensitive to long-term deformation (e.g., tall buildings, bridges), consider using the B3 model (Bažant-Baweja) or GL2000 model as recommended in ACI 209.2R-08.
The following table shows calculated ACI 209R-92 creep coefficients at different relative humidity levels for standard conditions: loading age t₀ = 7 days (moist cured, Type I cement), volume-to-surface ratio V/S = 3 inches. Values represent the creep coefficient φ(t,t₀) at different time durations after loading.
| Relative Humidity | γ_h Correction | φ Ultimate (φᵤ) | φ at 30 Days | φ at 90 Days | φ at 1 Year |
|---|---|---|---|---|---|
| 40% (Very Dry) | 1.002 | 3.24 | 1.46 | 2.02 | 2.59 |
| 50% (Dry Indoor) | 0.935 | 3.02 | 1.36 | 1.88 | 2.42 |
| 60% (Moderate) | 0.868 | 2.80 | 1.26 | 1.75 | 2.24 |
| 70% (Standard) | 0.801 | 2.59 | 1.16 | 1.61 | 2.07 |
| 80% (Humid) | 0.734 | 2.38 | 1.07 | 1.48 | 1.90 |
| 90% (Very Humid) | 0.667 | 2.16 | 0.97 | 1.35 | 1.73 |
Loading concrete at a later age significantly reduces creep — because older concrete has higher elastic modulus and lower creep potential. The table below shows φ at 1 year for different loading ages at standard conditions (RH = 70%, V/S = 3 in, Type I cement). Delaying loading from 7 days to 28 days reduces the 1-year creep coefficient by approximately 15%.
| Loading Age t₀ | γ_la Correction | φ Ultimate (φᵤ) | φ at 90 Days | φ at 1 Year | % Reduction vs. 7d |
|---|---|---|---|---|---|
| 3 Days | 1.094 | 2.83 | 1.76 | 2.26 | +9% |
| 7 Days (Standard) | 1.002 | 2.59 | 1.61 | 2.07 | — |
| 14 Days | 0.921 | 2.38 | 1.49 | 1.90 | −8% |
| 28 Days | 0.847 | 2.19 | 1.37 | 1.75 | −15% |
| 60 Days | 0.771 | 1.99 | 1.24 | 1.59 | −23% |
| 90 Days | 0.737 | 1.90 | 1.19 | 1.52 | −27% |
Concrete creep is influenced by a wide range of material, environmental, and structural factors. Understanding these factors helps engineers design more efficient structures and reduce unwanted long-term deformations. The ACI 209R-92 model accounts for the most critical variables through its correction factor system.
Lower ambient humidity accelerates drying creep. Desert climates (Las Vegas, Phoenix — 20–40% RH) produce significantly higher creep than coastal or humid climates (Miami, Houston — 75–90% RH). The γ_h correction factor ranges from ~1.0 at 40% to ~0.60 at 100% RH.
Concrete loaded earlier (3–7 days) creeps significantly more than concrete loaded later (28–90 days), because the C-S-H microstructure is still developing. Loading at 28 days instead of 7 days reduces total creep by approximately 15% per ACI 209R-92.
Larger members (higher V/S ratio) dry more slowly, reducing the drying creep component. Thin slabs (V/S ≈ 2 in) creep more than massive columns or walls (V/S ≈ 6–8 in). The γ_vs factor corrects for this geometry effect in the ACI 209R-92 model.
Higher-strength concrete (5,000–10,000 PSI) has a denser C-S-H microstructure and higher elastic modulus — both reduce creep potential. High-strength concrete (HSC) typically exhibits 20–40% less creep than normal-strength concrete under identical loading conditions.
The ACI 209R-92 model assumes a linear relationship between stress and creep — valid up to σ/f'c ≈ 0.40–0.45. Above this threshold (nonlinear creep zone), creep increases disproportionately and the linear model underestimates deformation. Always keep sustained stress below 45% of f'c.
Higher w/c ratios produce more porous concrete with greater creep potential. A concrete mix with w/c = 0.65 may creep 30–50% more than an equivalent mix with w/c = 0.40 under the same load. This is why low w/c, high-strength mixes are preferred for prestressed members.
Trusted standards, technical guides, and references for concrete creep and shrinkage in the United States.
The American Concrete Institute's official guide for modeling and calculating shrinkage and creep in hardened concrete. Documents the ACI 209R-92, B3, GL2000, and CEB MC90-99 prediction models with comparison data and worked examples for USA practice.
Visit ACIAASHTO LRFD Article 5.4.2.3.2 governs creep and prestress loss calculations for all US highway bridges. The FHWA provides detailed calculation examples for creep and shrinkage effects in prestressed concrete bridge girders using the AASHTO model.
Visit FHWAASTM C512/C512M is the standard test method for creep of concrete in compression. It covers the apparatus, specimens, loading procedure, and calculation of creep coefficient from laboratory measurements — the reference test behind all ACI creep prediction models used in the USA.
Visit ASTM