Structural Concrete - Hassoun

532 Chapter 15 Design for Torsion
Figure 15.8
Forces on section in torsion (space truss analogy).
Figure 15.9
Idealized torque versus twist relationship.
The behavior of a reinforced concrete beam subjected to pure torsion can be represented by
an idealized graph relating the torque to the angle of twist, as shown in Fig. 15.9. It can be seen
that, prior to cracking, the concrete resists the torsional stresses and the steel is virtually unstressed.
After cracking, the elastic behavior of the beam is not applicable, and hence a sudden change in the
angle of twist occurs, which continues to increase until the maximum torsional capacity is reached.