When a material is subject to loading, there is an immediate deflection. However, certain materials exhibit a long term deflection under sustained loading that increases gradually over time up to a certain limit. Such deflection is referred to as creep.
What is Creep?
As explained above,
If creep goes unchecked, it can pose a significant serviceability issue including excessive deformation, cracking, and loss of prestress.
Creep Over Time
The majority of creep takes place in the first year following the setting of the concrete. The graph below illustrates the general process (coming soon).
Creep Behavior of Different Materials
In the Japanese code, a creep factor is applied directly on the immediate deflection in order to estimate the long term deflection. Some creep factors are provided below.
| Material | Creep Factor | |
| Timber | 2 | |
| Steel | 1 | |
| Reinforced Concrete | Slabs | 16 |
| Beams | 8 | |
| Steel Reinforced Concrete | 4 | |
| Aluminum | 1 | |
| Lightweight ALC Panels | 1.6 | |
As you may observe above, steel and aluminium have a creep factor of 1.0. In other words, steel and aluminium do not suffer from creep effects.
Factors Affecting Creep
- Dryness of Concrete (drier = more creep)
- Member Size (smaller = more creep)
- Water-cement ratio (more water = more creep)
- Air content (more air = more creep)
- Magnitude of loading (higher = more creep)