...
Nominal axial compressive strength Pn is limited to a value of Pn,max in ACI Table 22.4.2.1.
...
For nonprestressed concrete members, Po shall be calculated by:
...
Strength reduction factors ϕ is determined according to using ACI Table 21.2.2. Since the section is compression controlled, a ϕ factor for compression control is used.
...
Strength reduction factors ϕ is determined according to using ACI Table 21.2.2. Since the section is tension controlled, a ϕ factor for tension control is used.
...
Nominal flexural strength Mn and axial strength are calculated based on the following Design Assumptions. While finding the flexural design strength, combined with axial force ϕMn, it should be found in which control zone the cross section is. When the section is tension controlled, a ϕ factor for tension control is used. When the section is compression controlled, a ϕ factor for compression control is used. When the section is within the transition region, ϕ is linearly interpolated between the two limit values.
...
Design assumptions
The flexural and axial strength of a member calculated by the strength design method, two basic conditions should be satisfied:
...
The distance between the fiber of maximum compressive stress and the neutral axis, c, is perpendicular to the neutral axis.
The value of β1 is determined using ACI Table 22.2.2.4.3.
...