Isolated footings are assumed to behave like beam cantilevers. Crossing a vertical plane through the footing and computing the moment due to the bearing pressure or the pile reaction acting on one side of that vertical plane determines the moment on the critical section of the footing. The critical section for flexure is taken at the face of the column. For round columns, Substructure converts the round column section to the equivalent square section. The face of the equivalent square will become the critical section.

Required steel as shown in the report is based on the actual moment and the minimum steel criteria for the appropriate code. In CHBDC, this is based on on Article 8.8.4.3 , which states that the minimum section capacity should be the smaller of 1.2 Mcr and 1.33 Mu. The program first checks if the section is adequate for the computed moment at the face of columns. It then checks if the design moment is at least equal to the minimum moment. This has to be at least equal to the smaller of 1.33 Mu and Mcr. If not, at least that capacity must be developed. If needed, revised steel is calculated. Then the program checks for temperate and shrinkage steel. However, the code specifies to distribute this in two faces. The program internally checks separately for top and bottom steel. In certain cases, it is possible that there is no moment in a section. In such a case, zero moment might be reported for combination number 0. However, temperature and shrinkage steel requirements have to be checked. Therefore, the program in LRFD mode will show required steel based on temperature and shrinkage.

In the case of negative pile reaction in a pile, top reinforcement may be needed, which is not computed by the program at this time.

For one-way shear calculations, the critical section is located at the distance, dv (for LRFD), or d (for LFD), both measured from the face of the column or equivalent square of the round column, as shown below (X-direction only). For shear capacity of the footing in LRFD mode, the program allows two approaches. By default, the program uses a simplified method as per Art. 5.8.3.4.1. However, the program also allows the use of the general method as per Art. 5.8.3.4.2. When using the general method, the program does two iterations to arrive at q (theta) and b (beta) values to be used in shear capacity calculations.

If a pile perimeter is completely outside the critical section (pile A) then the full pile reaction is considered in the subsequent pile cap design. However, no pile reaction is taken into account in the case where the pile perimeter is inside the critical section (pile B). For any pile location between Location A and B a linear interpolation of the pile reaction is performed to calculate the pile reaction

For two-way shear designs, the critical perimeter is determined using the average dv or d. The average dv or d are calculated using the dv or d in the global X or Z-direction. For a round column or pile, the circular profiles are used to determine the perimeter. If two round columns are close enough then their perimeters will merge and become one perimeter, as shown below.

Two-way shear is determined using the forces due to either the bearing pressure or pile reaction acting outside the critical perimeter.

When calculating the two-way shear for a pile and the pile is close to the edge of the pile cap, the perimeter might be cut by the edge. In this case, the two-way shear perimeter is taken by extending a tangent from the arc to the edge, as illustrated below.