Large amounts of transverse reinforcement are needed for reinforced concrete beams and columns in earthquake regions. This seemingly excessive reinforcement is necessary, however, to prevent concrete buildings from collapsing during an earthquake. Without extensive reinforcing, reinforced concrete structural members can behave in a brittle manner. A brittle beam or column deforms only a small amount before fracturing and losing its load-carrying ability. Ductile beams or columns carry loads even after undergoing large deformations.
The engineer is presented with two choices:
- use lower earthquake loads and design the structure for ductility
- use three to five times the earthquake loads prescribed by codes and don't design for ductility.
It is more economical to make the structure ductile. Bending or flexural ductility is obtained by using hoops or crossties in columns and closely spaced stirrups in beams.