Learn how to design a simple residential concrete spread footing in Calcs.com, including specifying soil properties, load, footing size, and reinforcement.
Sliding check: what the calculator models
The Spread Footing calculator (ACI 318-14, ACI 318-19, and IBC 2024 versions) computes sliding resistance using base friction only:
Sliding resistance = μ × (P + W_f)
where μ is the lateral sliding coefficient between concrete and soil, P is the ASD axial load, and W_f is the factored footing and soil self-weight. The sliding demand vs. resistance breakdown is shown when the results section is expanded.
Passive earth pressure is not modeled as a resistance term. There are no inputs for a passive pressure coefficient, embedment depth for passive resistance, or soil shear strength, and it is not listed in the assumptions.
