The reduced internal forces corresponding to the non-ductile behavior are automatically increased by the Ωo selected from Table 12.2-1.
In structural systems with high ductility level, the internal forces increased by the Ωo coefficient cannot be taken higher than the internal forces compatible with the yield state defined based on the principle of capacity design.
Ωo = Overstrength factor
Some elements of properly detailed structures are not capable of safely resisting ground-shaking demands through inelastic behavior. To ensure safety, these elements must be designed with sufficient strength to remain elastic. The load effect is approximated by use of an overstrength factor, Ω0, which approximates the inherent overstrength in typical structures based on the structure’s seismic force-resisting systems.
For reduced internal forces corresponding to the non-ductile behavior of the structural system elements, the Overstrength factor is used as the multiplier (Ωo > 1). These internal forces are internal forces that cause brittle collapse, such as shear force in reinforced concrete elements and forces acting on joints in steel elements.
For example, in a reinforced concrete column, the shear forces caused by earthquake effects are obtained by multiply with the overstrength factor, Ωo. Since the shear force shows brittle collapse behavior, internal forces caused by earthquake effects must be multiplied by the overstrength factor, Ωo according to 12.4.3 .