Concrete Footing

Concrete Footing

Size and check a square or rectangular isolated concrete footing for vertical loading. The module separates service-level soil bearing from strength-level concrete design and displays the calculation steps, reinforcing results, and diagrams.

Quick start

  1. Add a Concrete Footing calculation and enter a description.
  2. Choose Square or Rectangular. For a rectangular footing, enter the fixed footing width.
  3. Enter the footing thickness, clearance to ground, and square base-plate dimension. Follow the units displayed beside each field.
  4. Complete the material properties and soil design values.
  5. Open Loads and Combinations and enter the vertical loads in pounds, assigned to their correct load categories.
  6. Choose Design for required bars or Check for selected bars.
  7. Choose Run Model, then review the Design, Calculations, and Diagrams tabs. Correct any failed checks and run again.

Geometry and materials

The square option determines equal plan dimensions. The rectangular option uses the specified width and determines the required length. Enter the supported square base-plate size; it must be smaller than the footing. Thickness and clearance must leave sufficient effective depth for reinforcement.

Enter concrete strength f′c, reinforcing yield strength fy, and concrete density Wc. Review the displayed elastic modulus Ec and lightweight-concrete factor λ. The interface provides the two displayed Ec expressions and a shear-design table option. Select settings appropriate to the project; the presence of an option is not a determination that it applies to every footing.

Soil bearing

Enter the allowable bearing pressure from the project soil criteria. Use the displayed units: bearing pressures are in psf, and soil and concrete densities are in pcf.

The two weight options reduce the available bearing pressure by the footing weight and by the weight of soil above it. When the soil-above option is selected, enter the actual depth to the footing bottom; this cannot be less than the footing thickness.

Optional width and depth increases use the entered thresholds, percentage rate, and maximum bearing pressure. Enable these only when supported by the project soil criteria. The calculation output shows the deductions, applicable increases, and resulting allowable bearing pressure. A nonpositive revised capacity must be corrected before sizing can proceed.

Loads and combinations

Enter the individual vertical load cases, not a precombined total. Review their categories and the active combinations in Loads and Combinations.

The program evaluates service-level ASD combinations for bearing and identifies the controlling downward load. For the concrete design, the current implementation selects LRFD combinations using the load categories participating in that controlling ASD combination, or combinations containing those categories if no exact match exists. The Calculations tab lists the combinations actually considered and the governing factored load.

Always review both lists; completion of a calculation does not establish that every load scenario required for your project has been evaluated. With no loads entered, the module can display bearing information but cannot produce a complete loaded footing design.

Reinforcement and results

Design for required bars searches for reinforcement within the implemented design options. Check for selected bars uses the selected bar sizes and spacings. Rectangular footings have separate direction settings.

Review the calculated footing size, effective depths, required and provided steel, flexure, one-way shear, punching shear, bar spacing, and development checks. Use the diagrams to confirm direction, reinforcement arrangement, and geometry. The concrete calculations identify ACI 318-19 as their design reference.

A completed run is not necessarily a passing design. Read the final design status and detailed failures. If the thickness is inadequate, revise it and rerun; do not treat a proposed revision as an already accepted design.

Scope, saving, and reports

This workflow uses vertical loads, a square loaded area, and uniform soil pressure. It is not documentation of an eccentric footing, applied-moment, uplift, sliding, or overturning analysis. Check project conditions outside the implemented model separately.

Save the project to retain the inputs. Rerun after changing inputs and review the updated results. In the implementation used for this help page, the module’s standalone report command is not yet implemented; use the on-screen Calculations and Diagrams tabs for review.