The footing dimensions are calculated using a heuristic approach. The first trial section is sized using the user defined minimum footing dimension from the Optimization Criteria dialog box. If any of the dimensions are defined as fixed dimensions in the Assign Spread Footing Geometry dialog box then they are used. Once the footing has been dimensioned it is checked for soil stress capacity, flexure capacity on all four sides of the footing, one-way shear capacity on all four sides of the footing and two-way shear. The flexure reinforcement is designed before the footing shear is checked so that the reinforcement area can be used in calculating the section shear capacity.

If any of the checks fail, the appropriate dimensions of the footing are increased and the footing is rechecked. The dimensions that can be increased according to the Assign Spread Footing Geometry dialog box are increased using the increment values defined in the Optimization Criteria dialog box.

When the footing is found to pass all the checks mentioned above, a final check is performed using the optimized reinforcement diameters to properly account for the reinforcement depth.