D1.F.4.1 Strength and Ductility Design
The strength design is performed in two steps considering the longitudinal reinforcement design for axial-bending in an initial step, and the shear and torsion design including the longitudinal reinforcement for torsion tension in a latter pass together with the transverse design.
The member resistance is calculated based on strain compatibility and interaction surface calculations.
- ϕMn ≥ Mu
- ϕVn ≥ Vu
- ϕTn ≥ Tu
- ϕPn ≥Pu
ϕ is determined according to 21.2
The ratio of neutral axis depth to the depth of the furthest rebar in tension is limited such that the section strain at the location of the maximum rebar depth is a minimum of 0.004.
Application of the ductility checks are limited to cross sections with net axial load (compression) less than 0.10f´c Ag, in accordance with section 188.8.131.52.
The maximum strain in the tension reinforcement is calculated and compared with the Code limit. In order to reduce the time involved in the axial-bending calculations, the approximation may currently have a maximum difference with the more precise values of 12% mostly in biaxial cases, the approximation will be much better for other cases.