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IBC 2021ACI 318-19ASCE 7-16United States

Pole Footing (IBC 2021)

Column loads link directly from the beam or column calculation above, so changes propagate to the footing automatically. US structural engineers designing pier footings to ACI 318-19 - including deck posts, mezzanine columns, and foundations in high-wind areas or unstable soils where uplift governs. The uplift resistance model accounts for skin friction below the active soil zone, giving a more complete picture on variable soil profiles than a simple bearing check alone.

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What it calculates

Post and column loads link directly from the calculations above, so changes propagate to the footing automatically. Design pier and pole footings to ACI 318-19 per IBC 2021. Results cover lateral embedment, bearing, compression-bending interaction, shear, and uplift with skin friction resistance below the active soil zone.

Code standards

  • IBC 2021
  • ACI 318-19
  • ASCE 7-16

Who uses this calculator

Column loads link directly from the beam or column calculation above, so changes propagate to the footing automatically. US structural engineers designing pier footings to ACI 318-19 - including deck posts, mezzanine columns, and foundations in high-wind areas or unstable soils where uplift governs. The uplift resistance model accounts for skin friction below the active soil zone, giving a more complete picture on variable soil profiles than a simple bearing check alone.

Input allowable skin friction, bearing capacity, and active soil movement zone depth to verify resistance against uplift and downward forces. Uplift safety factor summary (restrained vs unrestrained) and resistance tables replace blunt uplift fail messages with a fuller assessment.

How it calculates

The Pole Footing (IBC 2021) calculator designs plain (unreinforced) concrete pier and pole footings to IBC 2021 and ACI 318-19. The pier is assumed to be continuously restrained against buckling by the surrounding soil, so unbraced length effects are neglected in the concrete compression checks.

Lateral embedment (IBC 2021, Cl. 1807.3)

The critical check for pole footings is lateral embedment - the depth needed to resist applied horizontal forces without excessive rotation. The IBC 2021 Cl. 1807.3 method uses:

  • Lateral stress at 1/3 depth S_(1/3): the design lateral soil stress at one-third of the embedment depth
  • Lateral stress at full depth S_d: the design lateral soil stress at the embedment depth

utilization = S_d / q_s ≤ 1.0

For nonconstrained piers (free to rotate at the top surface), the required embedment depth is solved iteratively from moment equilibrium. For constrained piers (fixed against lateral movement at grade by a floor slab or tie), a shorter depth may be required.

Vertical bearing

Gross vertical bearing pressure is the total downward service load divided by the pier base area:

utilization = q_gross / q_a ≤ 1.0

Compression and bending capacity (ACI 318-19, Ch. 21)

The pier is checked as a plain concrete compression-bending member. Nominal axial capacity P_n and nominal moment capacity M_n are calculated using ACI 318-19 Chapter 21 provisions for plain concrete. The combined interaction is evaluated:

utilization = (P_u / (phi × P_n)) + (M_u / (phi × M_n)) ≤ 1.0

The phi factor for plain concrete in combined loading is 0.60 per ACI 318-19.

Shear capacity (ACI 318-19, Ch. 21)

One-way shear demand at the critical section is compared to the plain concrete shear strength:

utilization = V_u / (phi × V_c) ≤ 1.0

Uplift safety factor

Uplift is checked two ways. Without skin friction:

FS_uplift = (W_pier + W_soil_above) / T_net ≥ required FS

With skin friction below the active soil zone:

FS_uplift_skin = (W_pier + W_soil_above + f_s × A_skin) / T_net ≥ required FS

The restrained and unrestrained uplift safety factors are reported separately.

Downward capacity check

A downward capacity check verifies that the pier can carry the maximum compressive service load including self-weight:

FS_down = (phi × P_n) / P_max ≥ 1.0

Concrete bearing at post-footing interface (ACI 318-19, Cl. 22.8)

Bearing stress at the post-footing interface is compared to the plain concrete bearing capacity. This check governs when concentrated point loads are transferred from a post or column into the top of the pier.

Related calculators

Pier Footing (ACI 318-14)→Wall Footing (ACI 318-14)→Wall Footing (ACI 318-19)→Rectangular Concrete Column→

Frequently asked questions

What design standards does this calculator use?
The calculator uses IBC 2021 for embedment requirements (Cl. 1807.3), ACI 318-19 for concrete capacity (Chapter 21 - compression, bending, shear, and bearing), and ASCE 7-16 for ASD and LRFD load combinations (Chapter 2). All three are applied simultaneously based on the check type.
What are the key inputs?
Key inputs are pier diameter (or rectangular dimensions), embedment depth, height above ground, concrete strength and weight class, post or column type (round post, rectangular post, or steel with base plate), lateral constraint condition at the ground surface (constrained or nonconstrained), allowable vertical bearing pressure, allowable lateral soil stress at one-third embedment depth and at full depth, skin friction value, and active soil movement zone depth. Applied loads include vertical (dead, live, wind) and lateral (wind, seismic) in both plan directions.
What checks does the calculator perform?
The calculator checks: lateral embedment (IBC 2021, Cl. 1807.3) comparing lateral soil stress demand to allowable; vertical bearing pressure versus allowable; compression and bending interaction (ACI 318-19, Ch. 21); one-way shear capacity; uplift safety factor (with and without skin friction); downward capacity; and concrete bearing at the post-footing interface. All checks report demand, capacity, and utilization.
How is lateral embedment depth determined?
The calculator uses IBC 2021 Cl. 1807.3 methodology. For nonconstrained piers (free at top), the embedment depth required to resist the applied lateral load is calculated from the lateral soil stress profile at one-third depth and at full depth. For constrained piers (fixed against lateral movement at grade), a shorter embedment may be acceptable.
How does the uplift check account for skin friction?
The uplift safety factor is calculated two ways: without skin friction (using only self-weight and vertical bearing resistance) and with skin friction below the active soil zone. The active soil zone depth is entered as an input; skin friction resistance acts only on the pier surface below that depth. This provides a realistic uplift capacity for sites with seasonal soil movement, expansive soils, or frost depth effects.
Can I link column loads to this pier footing calculator?
Yes. If a column or post calculation sheet exists above the footing in the same Calcs.com project, the axial and lateral reactions can be linked directly. When the column calculation updates - for example due to a load change or span revision - the footing automatically re-runs all bearing, shear, and uplift checks with the updated loads.

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