Stiffening Effect of Concrete in the Tension Zone
In cracked reinforced concrete components, the tensile forces in the crack are absorbed solely by the reinforcement. However, between two cracks, tensile stresses are introduced into the concrete through the (slidable) bond. Thus, the concrete participates in the absorption of internal tensile forces, leading to an increase in the stiffness of the component. This effect is referred to as the stiffening contribution of concrete to tension between the cracks, or as tension stiffening.
The consideration of an increase in component stiffness due to tension stiffening can be done in two ways:
- Representation using the tensile strength of concrete
A remaining, constant residual tensile stress that remains after cracking can be involved in the concrete stress-strain curve. The residual tensile stress is significantly lower than the tensile strength of the concrete. Alternatively, modified stress-strain relationships for the tension area can also be introduced, which, through a descending branch after reaching the tensile strength, take into account the contribution of concrete in tension between the cracks.
In RFEM 6, the following three approaches are offered for considering tension stiffening for modeling the tensile strength of concrete.
- Quast
- Quast modified
- Hsu and Mo
- Representation using a modified steel curve
Another variant involves changing the "bare" stress-strain curve of the reinforcing steel. Here, a reduced steel strain εsm is applied in the cross-section under consideration, which results from εs2 and a deduction term due to tension stiffening.