算BuildCalc Get a quote

Base Plate Design Calculator

§ Code basis: AISC Design Guide 1 (United States) — The design equations differ, so the values are not interchangeable - recalculate with your own code.

Thicker is not the answer — check the bearing area first, then the cantilever.

Also known as base plate design · column base plate · steel column base detail

Quick answer

With the default inputs: Column axial load P 1500 kN · Concrete f'c 30 MPa · Steel yield Fy 250 MPa etc.Required plate thickness 24.7 mm

Use your own dimensions ↓

Inputs

kN
MPa
MPa

Result

Required plate thickness
24.7mm
Concrete bearing strength16.57MPa
Required area90.5cm²
Provided area122.5cm²
Bearing pressure fp12.24MPa
Bearing utilisation74%
Cantilever m (along depth)32.5mm
Cantilever n (along flange)55.0mm
Yield-line n′75.0mm
Governing cantilever75.0mm
Suggested thickness26mm
Bearing checkPass
How this is worked out

The usual mistake is fixing the plate size first and checking afterwards. The order is the other way round: divide the axial load by the concrete bearing strength to get the minimum area, add a margin of two to three bolt diameters or at least 50 mm beyond the column, then compute thickness. Concrete bearing is only phi_c 0.85 f′c, 16.6 MPa for C30, against 250 MPa of steel — a factor of 15 — so the area is always governed by the concrete and the thickness only has to spread the column load over it. The thickness formula comes from a cantilever strip, t = l sqrt(2 fp / (0.9 Fy)), where l is the largest of m, n and n′ = sqrt(d·bf)/4. That third term is the yield-line projection between the flanges and it grows as the column gets squarer — for this 300×300 column n′ is 75 mm against m 32.5 and n 55, so it actually governs the thickness. DG1 carries a reduction factor lambda no greater than 1; this tool takes lambda = 1.0, which is conservative. Note the square root: doubling the pressure raises thickness by 41%, while doubling thickness quadruples bending resistance. Bearing strength here also assumes sqrt(A2/A1) = 1, so no confinement bonus is claimed even where the pier is much larger than the plate — again conservative, and worth up to a factor of two when you do apply it. When a plate is overstressed, enlarging it to cut fp is far cheaper than thickening it — thickness buys capacity with the square of the money.

Next up: Steel Beam Span Calculator · Section Properties Calculator

Formula

Bearing strengthfp,max = φc·0.85·f'c, φc = 0.65
Required areaAreq = P/fp,max
Bearing pressurefp = P/(B·N)
Cantileverm = (N − 0.95d)/2, n = (B − 0.8bf)/2, n′ = √(d·bf)/4
Governingl = max(m, n, n′)
Thicknesst = l·√(2fp/(0.9Fy))
1500 kN on C30 with Fy 250 MPa, a 300×300 column and a 350×350 plate: bearing strength 16.58 MPa, 90.5 cm² required against 122.5 cm² provided, pressure 12.24 MPa, cantilevers 32.5, 55.0 and n′ 75.0 mm, l 75.0 mm, 24.7 mm required and 26 mm suggested.

Basis

The codes below are listed for comparison. This calculator returns AISC Design Guide 1 values only.

FAQ

How thick should a base plate be?
Treat it as a cantilever. The projection beyond the column carries the uniform bearing pressure, so a unit-width strip sees M = fp l²/2 and needs t = sqrt(4M/(0.9 Fy)), which reduces to t = l sqrt(2 fp / (0.9 Fy)). Take l as the largest of m = (N − 0.95d)/2, n = (B − 0.8bf)/2 and n′ = sqrt(d·bf)/4. At 1500 kN on C30 with a 350×350 plate and a 300×300 column: 12.24 MPa, m 32.5, n 55 and n′ 75 which governs, so 24.7 mm required and 26 mm specified.
What if the plate area is too small?
Add area, not thickness. Pressure is P/(B N), so doubling the area halves it and cuts thickness to 71%, whereas doubling thickness costs money squared. In practice you enlarge the plate to the required area first and then check that bolts and stiffeners still fit. Where the layout forbids a larger plate, raise the concrete strength or use local reinforcement such as a grout pad or spreader.
Why is grout needed under a base plate?
Because plate and concrete never meet perfectly. With no grout, contact is limited to a few high points and the local pressure multiplies many times over; the concrete crushes, the plate settles and the column goes out of plumb. Non-shrink grout spreads the load evenly, typically 25 to 50 mm thick. Watch the strength — grout is usually weaker than the foundation concrete, so where the bed is thicker than 50 mm the bearing check must use the grout strength, not the base strength.
How do base plate and anchor bolts work together?
The bolts take uplift and shear, the plate takes bearing — different jobs. Edge distance must be at least 1.5 bolt diameters and no less than 40 mm, or the plate tears out. Under moment one side of the column goes into tension and the bolt force has to travel through the plate cantilever, so thickness is often governed by bolt tension rather than bearing; check both cases.

Cite this page

Use this format in reports, method statements or coursework. The link is permanent.

Building Calculator. Base Plate Design Calculator. 2026-10-25. https://jianzhujisuan.com/en/base-plate

Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.