Confinement (structural)

Concrete is a very brittle material and it can easily split in tension. On the other hand, steel reinforcement is strong in tension. In most cases, concrete and steel bars are met together on structural members of a structure. During earthquake the demand, on reinforced concrete members, increases. Using a smaller spacing of stirrups and therefore higher ductility, a confinement zone is introduced. This confinement zone enhances the ductility of the member, which means it can undergo larger deformations before failing. The confinement zone also helps to distribute the forces more evenly throughout the member, reducing the likelihood of local failure. Furthermore, when a reinforced concrete member undergoes cyclic loading during an earthquake, it goes through a series of hysteresis energy curves. This means that the member is able to dissipate energy as it undergoes multiple cycles of loading and unloading. The introduction of a confinement zone increases the hysteresis energy dissipation capacity of the member, improving its overall seismic performance.