In SP-16, Design charts for combined axial compression and bending are given in the form of interaction diagrams in which curves for Pu/fckbD versus Mu/fckbD² are plotted for different values of p/fck, where p is the reinforcement percentage. Charts for rectangular sections have been given for reinforcement equally distributed on two sides (charts 27 to 38) & for reinforcement equally distributed on four sides (charts 39 to 50). In STAAD Pro, during design of a concrete column member using IS456 code, user can specify the face of the column for longitudinal bar arrangement using the RFACE parameter. There are three options, RFACE 2 - reinforcement shall be placed along the 2 edges parallel to local Z axis RFACE 3 - reinforcement shall be placed along the 2 edges parallel to local Y axis RFACE 4 - reinforcement shall be placed on four sides Now, let us under stand the local Y and Z axis of member. In STAAD Pro Property window is being seen as below: As you can see, YD is depth