Which of the following is a time-dependent prestress loss in pretensioned concrete?

In pretensioned concrete, the primary time-dependent loss of prestress comes from the relaxation of the prestressing steel. This phenomenon occurs due to the viscoelastic nature of the steel, which allows it to gradually lose stress over time under constant strain. As the tendons are tensioned and then released, they initially exert a certain level of stress on the surrounding concrete. However, over time, as the steel relaxes, the stress within the tendons decreases, leading to a reduction in the effective prestress transferred to the concrete.

Creep, while related to the time-dependent behavior of concrete under stress, primarily refers to the deformation of concrete over time. It is not a direct loss of prestress but rather a change in the concrete's dimension. Shrinkage is also a time-dependent phenomenon, where the concrete reduces in volume as it dries, but it does not directly account for the loss of prestress in the steel itself. Yielding refers to the point at which a material deforms plastically, but this is not a typical concern for prestressing steels in practice, as they are designed to avoid yielding during normal service loads.

The relaxation of prestressing steel is critical to understand as engineers design and analyze prestressed concrete elements