Tension stiffening

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.

Stress Behavior Between Primary Cracks

The increase of the structural component stiffness due to tension stiffening can be considered in two ways:

- Representation by means of tensile strength of concrete

Es kann eine verbleibende, konstante Restzugspannung, welche nach der Rissbildung erhalten bleibt, in der Betonarbeitslinie involviert werden.Die Restzugspannung ist dabei deutlich kleiner als die Zugfestigkeit des Betons.
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.

In RFEM 6 werden für die Berücksichtigung von Tension Stiffening die folgenden drei Ansätze für die Modellierung der Betonzugfestigkeit geboten.

• Quast
• Modified Quast
• Hsu and Mo

- Abbildung mittels modifizierter Stahlkennlinie

Another approach is to modify the "pure" stress-strain diagram of the reinforcing steel.
In this case, a reduced steel strain ε_sm is applied in the relevant cross-section, with the strain resulting from ε_s2 and a reduction term due to the tension stiffening.