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The design frost penetration at this site.
Take it from the local authority's adopted figure rather than from experience of recent winters. Bare, snow-cleared ground freezes far deeper than the same soil under undisturbed snow cover, and a driveway or a stripped construction site is the bare case.
The outside diameter of the pier shaft through the frost zone.
Bonded area grows with diameter while the concrete's own restraint grows with the square of it, so a fatter shaft is not automatically worse — but a rough, corrugated or over-drilled shaft develops more bond than a smooth cased one at the same diameter. Reflect the finish in the bond stress you enter, not here.
The bond stress developed between frozen soil and the shaft face.
This is the input that governs the answer, and it is not a constant of nature. It depends on the soil's frost susceptibility, its water content, how fast the ground froze and how rough the shaft surface is, and it can vary by a factor of several across those conditions. It belongs to your geotechnical report. Where no report exists, the honest response is to test a range and see whether the conclusion changes rather than to trust one figure.
The permanent load the pier carries, with no live or snow contribution.
Dead load only, and deliberately so. Adfreeze acts hardest in deep winter on a structure that may be unoccupied, unloaded or not yet finished, so counting live load as restraint assumes the one thing you cannot rely on. A deck that heaves is usually a deck that was empty when it moved.
Depth from finished grade to the underside of the base or bell.
This sets the concrete self-weight and the depth of soil standing over the bell. Where the pier is shallower than the frost depth entered above, the bonded zone is capped at the pier's own length — a pier cannot be gripped over ground it does not reach.
Diameter of the bell or footing pad at the base of the pier.
Only the part of the bell that projects beyond the shaft does any anchoring work, and what it mobilises is the soil standing directly over that projecting ring. Enter a diameter equal to or below the shaft to model a straight shaft with no bell at all — the restraint from it then falls to zero.
Bulk density of the soil resting over the projecting bell.
Use the moist bulk density of the backfill and native ground above the bell. Where the water table sits above the bell, the submerged weight is roughly the bulk figure less the density of water, and using the dry figure there overstates the restraint.
Combined cross-sectional area of the vertical bars, in square millimetres.
Count only bars that run continuously from the bell into the cap or the structure above and are developed at both ends. Four 16 mm bars give about 804 mm²; four 20 mm bars give about 1,257 mm². Bars that stop short of the bell carry no uplift, however many there are.
Net uplift on the pier
13.3 kips
Adfreeze exceeds the restraint, so the vertical steel is in tension and has to be developed into both the bell and the cap. The bond stress you entered governs this answer — run it high and low before treating the result as settled.
- Adfreeze uplift on the shaft
- 20.88 kips
- Restraint from dead load, pier and bell
- 7.55 kips
- Tension the vertical steel must carry
- 13.33 kips
- Stress in the vertical steel
- 10,753.32 psi
- Bonded shaft area inside the frost zone
- 15.38 ft²
They open the calculator with your figures already in it
Pier Adfreeze Uplift Calculator: 13.33 kips — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Uplift = adfreeze bond stress × the shaft's bonded surface area inside the frost zone (π × diameter × frost depth). Restraint = dead load + pier self-weight + the weight of soil standing over the bell's projecting annulus.
- The adfreeze bond stress is a SITE-SPECIFIC soil property you supply from the geotechnical report; this page applies no table of published values, because bond stress varies with soil type, moisture, freezing rate and shaft finish.
- ASCE/SEI 32, Design and Construction of Frost-Protected Shallow Foundations — the standard the frost-heave design case belongs to
- ACI 318, Building Code Requirements for Structural Concrete — the code governing development of the vertical bars that carry the tension computed here
- Normalweight concrete self-weight taken as 2,400 kg/m³ (about 150 pcf), the conventional design value
Inputs used
- Design Frost Depth
- 5 ft
- Shaft Diameter
- 11.75 in
- Adfreeze Bond Stress
- 9.43 psi
- Dead Load Carried
- 4.5 kip
- Total Pier Depth
- 8 ft
- Bell or Pad Diameter
- 24 in
- Soil Bulk Density
- 112.37 pcf
- Vertical Steel Area (mm²)
- 800
Intermediate steps
- Adfreeze uplift on the shaft
- 20.88 kips
- Restraint from dead load, pier and bell
- 7.55 kips
- Tension the vertical steel must carry
- 13.33 kips
- Stress in the vertical steel
- 10,753.32 psi
- Bonded shaft area inside the frost zone
- 15.38 ft²
Confidence note: Adfreeze exceeds the restraint, so the vertical steel is in tension and has to be developed into both the bell and the cap. The bond stress you entered governs this answer — run it high and low before treating the result as settled.
What this calculation does not cover
- This is a single-pier force balance. It does not check bearing, lateral capacity, bar development length or the bell's own structural strength.
- Heave forces from ice lensing beneath the base are a separate mechanism and are not included.
- Group effects, sloping ground and a pier alongside a heated structure all change the frost regime and are outside this calculation.
Add the equipment this sizes
This result is a specification — 13.3 kips — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-08-30 · in the site-wide review of 2026-09-06 · v1.0.0
Regulatory standards & verification citations5
- Uplift = adfreeze bond stress × the shaft's bonded surface area inside the frost zone (π × diameter × frost depth). Restraint = dead load + pier self-weight + the weight of soil standing over the bell's projecting annulus.
- The adfreeze bond stress is a SITE-SPECIFIC soil property you supply from the geotechnical report; this page applies no table of published values, because bond stress varies with soil type, moisture, freezing rate and shaft finish.
- ASCE/SEI 32, Design and Construction of Frost-Protected Shallow Foundations — the standard the frost-heave design case belongs to
- ACI 318, Building Code Requirements for Structural Concrete — the code governing development of the vertical bars that carry the tension computed here
- Normalweight concrete self-weight taken as 2,400 kg/m³ (about 150 pcf), the conventional design value
Which documents these citations point at
Standards referenced: ACI 318 (American Concrete Institute, United States).
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