30 - 05 Nov 2025
Time-Dependent Effects
Estimated Time: 5–6 min quiz | PDH/CPD: 1.5 hr | Difficulty: Advanced
Question (Numerical)
A 120m cantilever span shows 85mm initial deflection under permanent loads. With a creep coefficient of 2.2 and shrinkage strain of 200×10⁻⁶, calculate the total long-term deflection using simplified analysis methods. Assume effective depth is 2.5m and prestress reduces deflection by 25%.
Calculation (Simplified Methods):
1.Creep deflection = 85mm × 2.2 = 187mm
2.Shrinkage deflection = (200×10⁻⁶) × (120,000²)/(8×2,500) = 144mm
3.Total deflection = 85 + 187 + 144 = 416mm
4.With 25% prestress reduction = 416 × 0.75 = 312mm ≈ 310mm
Explanation: Long-term deflections combine initial elastic deformation, creep (time-dependent under sustained load), and shrinkage effects. Simplified methods provide reasonable estimates for preliminary design, though detailed analysis requires consideration of construction sequence and variable environmental conditions.
Learning Resources:
ACI 209R-92 - Prediction of creep, shrinkage, and temperature effects in concrete structures
AASHTO LRFD Bridge Design Specifications (2020), Section 5.4.2.3 - Time-dependent material properties
fib Model Code 2010, Chapter 5 - Constitutive laws for time-dependent analysis