Optimization of Footing Dimensions

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 dimension in the Assign > Geometry > Spread Footing dialog box then they are used. Once the footing has been dimensioned it is checked for soil stress capacity, one-way shear capacity on all four sides of the footing, two-way shear and flexure capacity on all four sides of the footing.

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 > Geometry > Spread Footing 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.

Optimization of Reinforcement

The reinforcement selection required to resist flexure in a footing is performed according to the user-defined criteria on the Reinforcement Selection tab of the Criteria > Design dialog box. The final optimized reinforcement selection will always adhere to all ACI code limits regarding reinforcement spacing, reinforcement area ratios, and development length.

From the list of the acceptable flexure reinforcement sets (quantity and size of bars), the best-fit set is selected given the users preference. In the selection of the best fit reinforcement set, the optimization method does make provisions for sets that may have very similar optimization limits. For example, when optimizing for minimum reinforcement area if the following two bar sets were found to be acceptable: (10) #6 (4.4 ) and (40) #3 (4.4 ) the (10) #6 would be selected as the optimum reinforcement over the (40) #3.

If the option Keep all bars in Layer the same is selected on the Reinforcement Selection tab of the Criteria > Design dialog box, the reinforcement parallel to both the major and minor axis will be considered in finding the optimum reinforcement. Note that a Layer contains both the Length and Width direction reinforcement for flexure in a given direction. This is performed independently for the reinforcement at the bottom of the footing and at the top of the footing.