The ultimate soil analysis footing output page displays the bearing pressures in each orthogonal direction on the strip / footing. These pressures are then used to complete the concrete design of a soil supported foundation.
By default, the factored or ultimate soil pressures displayed on this page are computed using uniaxial bending values along each orthogonal direction. Loads in each orthogonal direction are considered to determine the maximum and minimum bearing pressures at the base of the footing and then these pressures are used to determine shears and moments in the footing in each orthogonal direction.
Note: In certain cases the Max and Min bearing pressures values may show reversed values. In other words, the max bearing pressure value may be listed under Min bearing pressure and vice versa. This situation simply indicates that the loads most likely are directed opposite to the positive sign convention of the loads.
For an irregular footing type, the pressures are listed for each strip and these pressures are used to complete the concrete design of the strip. For more information on strip notation, refer to Footing Strips.
If biaxial bending pressures are to be considered in determining the shears and moments, select the option "Consider biaxial bending pressure for concrete design" on the Defaults tab of workspace settings.
Considering Biaxial Bending Pressure for Concrete Design:
Linear Soil Pressure Method:
When this option is selected on the Defaults tab of workspace settings, factored or ultimate pressures at the four corners of a rectangular footing are determined for each load combination based on a trial and error solution. The maximum pressure and the corresponding minimum pressure in each direction are then used to determine the shears and moments in the footing in each orthogonal direction. This method is only used for footings containing at the most 4 piers. For number of piers exceeding 4, the default method of determining pressures in each orthogonal direction based on axial load and uniaxial bending is considered for completing the concrete design.
For octagonal/circular footings supporting multiple load points, the concrete design is completed assuming effective dimensions of the octagon/circle by obtaining the square area equivalent to that of the octagon/circle area.
Reduced Effective Area Method:
When this option is selected on the Defaults tab of workspace settings, factored or ultimate pressures are determined for each load combination based on the effective area. This pressure is then used to determine the shears and moments in the footing in each orthogonal direction. This method is only used for footings containing at the most 4 piers. For number of piers exceeding 4, the default method of determining pressures in each orthogonal direction based on axial load and uniaxial bending is considered for completing the concrete design.
For octagonal/circular footings supporting multiple load points, the concrete design is completed assuming effective dimensions of the octagon/circle by obtaining the square area equivalent to that of the octagon/circle area.
If the non-contact area between the footing and the soil exceeds the value specified on the Defaults tab of workspace settings, the load combination rows for factored load combinations that result in this condition are displayed in color to indicate that the non-contact area criteria is not being met.
Strap Footings:
This page only shows the two footing tabs each with a sub tab Bearing Capacity. The output results display the maximum bearing pressure, load eccentricity and the reaction force under each footing. These values are used for concrete design of the two footings and the strap beam.