Shrinkage warping results in a time dependent curvature on a reinforced concrete section and a time dependent deflection of a reinforced concrete flexural member. The curvature is caused by the shrinkage internal force (D T). When the internal force cause bottom cracking, the section properties of concrete are reduced, allowing an increase in curvature. Therefore, the curvature due to drying shrinkage is greater on cracked sections than uncracked sections. The shrinkage stresses and strains on an uncracked section are shown in Figure 2.
Figure 2: Shrinkage stresses and strains on an uncracked section
The shrinkage stresses on a fully cracked section are shown in Figure 3.
Figure 3: Shrinkage stresses and strains on a fully cracked section
As the concrete shrinks, the tensile stress gradually increases, creating curvature and gradual warping of the beam. The amount of curvature depends on the size of the concrete member and the magnitude of the cracking.