Stiffening Effect of Concrete in Tension Zone
In cracked reinforced concrete elements, the tensile forces in the crack are absorbed solely by the reinforcement. Between two cracks, however, tensile stresses are introduced into the concrete via the (displaceable) bonding. The concrete thus participates in absorbing internal tension, which leads to an increase in the stiffness of the structural component. This effect is referred to as the stiffening effect of concrete on tension between the cracks, or tension stiffening.
The increase in component stiffness due to tension stiffening can be taken into account in two ways:
– Modeling via Tensile Strength of Concrete
A remaining, constant residual tensile stress, which remains after the crack formation, can be included in the concrete stress-strain diagram. The residual tensile stress is significantly smaller than the tensile strength of the concrete.
Alternatively, modified stress-strain relations for the tension area can be introduced, which take into account the contribution of the concrete to tension between the cracks via a decreasing branch after reaching the tensile strength.
In RFEM 6, the following three approaches for modeling the tensile strength of concrete are provided for considering tension stiffening.
- Quast
- Quast modified
- Hsu and Mo
– Modeling via Modified Characteristic Steel Curve
Another variant involves changing the “bare” working line of the reinforcing steel.
Here, a reduced steel strain εsm, which results from εs2 and a deduction term due to tension stiffening, is applied in the analyzed cross-section.