ABSTRACT
Concrete is strong in compression, but weak in tension: its tensile strength varies from 8 to 14% of its
compressive strength. Due to such a low tensile capacity, flexural cracks develop at early stages of loading.
In order to reduce or prevent such cracks from developing, a concentric or eccentric force is imposed in
the longitudinal direction of the structural element. This force prevents the cracks from developing by
eliminating or considerably reducing the tensile stresses at the critical midspan and support sections at
service load, thereby raising the bending, shear, and torsional capacities of the sections. The sections are
then able to behave elastically, and almost the full capacity of the concrete in compression can be
efficiently utilized across the entire depth of the concrete sections when all loads act on the structure.
