Stiffening Effect of Concrete in Tension Area
In cracked parts of the reinforced concrete, the tensile forces in the crack are resisted by the reinforcement alone. Between two cracks, however, tension stresses are transferred to the concrete through the (displaceable) bond. Thus, the concrete contributes to the resistance of the internal tensile forces, which leads to an increased stiffness of the structural component. This effect refers to the stiffening contribution of the concrete in tension between the cracks, and is also called tension stiffening.
The increase of the structural component stiffness due to tension stiffening can be considered in two ways:
Modeling via Concrete Tensile Strength
A constant residual tensile stress, which remains after the crack formation, can be involved in the concrete stress-strain diagram. The residual tensile stress is significantly lower than the tensile strength of the concrete.
Alternatively, it is also possible to introduce modified stress-strain relations for the tension zone that consider the contribution of the concrete in tension between the cracks in the form of a decreasing branch in the graph after the tensile strength is reached.
RFEM 6 provides the following three approaches for modeling the concrete tensile strength in order to consider tension stiffening.
- Quast
- Modified Quast
- Hsu and Mo
Modeling via Modified Characteristic Curve for Steel
Another approach is to modify the "pure" stress-strain diagram of the reinforcing steel.
In this case, a reduced steel strain εsm is applied in the relevant cross-section, with the strain resulting from εs2 and a reduction term due to the tension stiffening.