Combined Footing

Two-column footing — pressure, beam V/M envelope, punching & flexure (ACI 318).

Enter service (unfactored) loads — the tool applies the 1.2D + 1.6L strength combination internally. Allowable soil bearing q_allow is a geotechnical (service-level) input from the soils report.

Design diagram — updates live with your inputs

Columns & Loads

Column 1 dead (lb) Service

Column 1 live (lb) Service

Column 2 dead (lb) Service

Column 2 live (lb) Service

Column spacing (ft) Center to center

Edge to column 1 (ft) Left edge to first column

Column size (in) Square (punching)

Footing & Soil

Allowable soil bearing (psf)

Footing length L (ft)

Footing width B (ft)

Footing thickness h (in)

Concrete & Reinforcement

Concrete f'c (psi)

Reinforcement fy (psi)

Longitudinal bar

Clear cover (in)

ACI 318-19 / IBC 2021

Validation, assumptions & limitations Download validation report (PDF) ↗

This calculator is verified by 4 independent tests comparing its output against closed-form statics, NDS/SDPWS design-standard values and published worked examples. Full case-by-case results are in the PDF report.

Assumptions

Rectangular footing; uniform soil pressure (size for e->0).
Analysed as a longitudinal beam (uniform up, two column point loads).
Strength loads for concrete; service for soil bearing.

Limitations

Allowable soil bearing is a geotechnical input.
Uniform-pressure idealisation (trapezoidal only via q_max check).
Transverse 'beam strips' under each column not separately designed here.

Results are for preliminary design and must be confirmed by a licensed engineer against the current adopted code and project-specific conditions.