Combined Footing Calculator, ACI 318-19

What it checks

The module designs a two-column combined footing by evaluating the structural response of the concrete element under gravity loads. It utilizes both service and strength design methods, deriving service loads for bearing pressure checks and factored loads for concrete capacity checks from the same input data. The sequence of checks begins with the determination of governing load combinations. The module evaluates both columns under the same combination to ensure the footing is designed for the case maximizing the total load. It then calculates the combined bearing pressure, followed by one-way and punching shear checks at each column location. Finally, the module determines the required flexural steel for the footing.

Inputs

Column Loads - Dead and live loads by basic load case in kips, unfactored. Supplying these values activates the combination engine to derive both service and factored loads.
Load Combinations - Project-specific load combination configurations. If absent, the module falls back to default ASCE 7-22 sets.
Seismic Parameters - Site coefficient SDS value. If provided and greater than zero, the vertical seismic effect is folded into seismic combinations.

What it reports

Service Combination - The specific ASD combination label that produced the loads used for bearing pressure calculations.
Strength Combination - The specific strength combination label that produced the design loads for concrete checks.
Load Warning - A message flagging inconsistencies if supplied pre-factored loads do not match a valid ASCE 7 gravity combination, naming both columns.
Bearing Pressure - The combined bearing pressure resulting from the service loads, compared against allowable soil capacity.
Shear Capacity - One-way and punching shear results at each column, evaluated against the concrete shear strength.
Flexural Steel - The required steel area for flexure, derived from the factored moments.

Code references

The engine cites ACI 318-19 §22.5 and §22.6 for concrete design requirements, and ASCE 7-22 §2.4 for bearing and load combination standards.

Limits

The module assumes that if project load combinations are not supplied, the default ASCE 7-22 sets are appropriate. It does not evaluate columns under different load cases; both columns are always combined under the same governing combination. If pre-factored loads are supplied, the module flags inconsistencies but does not correct them. Results are engineering aids; the engineer of record is responsible for the design.

This module ships in the desktop app

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