In order to handle complex conditions like compression reinforcing, multiple layers of reinforcing, and shapes other than simple rectangles, ENERCALC uses a powerful reinforced concrete section solver that evaluates the strain diagram for the cross section. Why does the Concrete Beam module report a different area of steel required or a different reinforcing ratio required as compared to hand calcs based on first principles? In these situations, it's necessary to apply engineering judgment to verify that the design meets minimum steel requirements for ductility. This difference means that it is possible in some instances to see a result that shows that the section has the necessary moment capacity, but appears to fail the reinforcing area requirements. In other words, the As Required column in MVD Summary > LRFD Shears & Moments is conservatively ignoring the effects of any compression reinforcing. The minimum steel calculation looks at minimum steel, (4/3) of minimum steel, and the flexural steel required to satisfy the basic formula of phiMn = phi As Fy (d - a/2). The calculation of phiMn is done with a very detailed dedicated solver that considers the location of the neutral axis under the applied load and the beneficial effects of compression steel, if any exists. Why does the Concrete Beam module say to 'Check As Min Limits' when it also says phiMn > Mu?
