Pole Footing (IBC 2021)

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.

This calculator uses an earlier code edition (IBC 2021 (ACI 318-19 and ASCE 7-16)). It stays available for existing projects. For new designs, check the [Calculator Library](/docs/calculators/us) for the current edition. ## Method & scope | Property | Detail | | ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | Design standards | IBC 2021 (ACI 318-19 and ASCE 7-16) | | Regions | United States | | Who it's for | 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. | | What it checks | Lateral embedment (IBC 2021, Cl. 1807.3), Vertical bearing, Compression and bending capacity (ACI 318-19, Ch. 21), Shear capacity (ACI 318-19, Ch. 21), Uplift safety factor, Downward capacity check, Concrete bearing at post-footing interface (ACI 318-19, Cl. 22.8) | #### What it calculates 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. #### Calculation method 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. ## How to use it Open it from **Run calc** in the About this calculator panel above. Work through the input sections from top to bottom. Click any input label to see its reference explanation, clause, conditions and assumptions. See [Checks, References, Conditions and Assumptions](/docs/running-calculations/checking-results/checks-references-conditions-assumptions). Check the utilization of each governing check in the summary, then export a PDF report. See [Views and Export](/docs/running-calculations/exporting-reports/views-and-export). ## Common questions 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. 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. 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. 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. 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. 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. ## Next steps Complete list of Calcs.com design calculators available for United States projects (AISC, ACI, NDS, ASCE 7, IBC, and related standards). Design combined rectangular footings for two columns to ACI 318-19 per IBC 2024: bearing, overturning, sliding, flexure, shear and development length. Design steel screw piles to AS 2870:2011 and AS 2159:2009. Ultimate bearing and serviceability with geotechnical risk rating and corrosion allowance. Design pier and deck footings to ACI 318-14 (IBC 2018). An earlier code edition, kept for existing projects. Design continuous wall footings to ACI 318-14. An earlier code edition, kept for existing projects.