Check concrete bearing strength under a base plate to AS 3600:2018 Clause 12.6, with A2 grown from the plate to the nearest edge. Try it free.
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About this Concrete Bearing Under a Base Plate Calculator
This calculator works out the design bearing strength of the concrete under a base plate or anchor plate and checks it against the bearing stress, to AS 3600:2018 Clause 12.6. Concrete confined by more concrete around the loaded area can take a higher bearing stress than its cylinder strength, up to a limit. The page builds the supporting area A2 from the plate and its distances to the member edges, or takes A1 and A2 as entered.
- Structural engineer checks column base plates on footings, pedestals and pile caps, especially where a plate sits close to an edge.
- Steel connection designer confirms the concrete under a base plate alongside the AS 5216 anchor checks for the same connection.
- Bridge and civil designer checks bearing under plates and bearings where the supporting surface is limited by nearby edges.
It is an engineering-grade CalcTree calculation with a plan of A1 and A2, and every step stays live and auditable.
More info on Concrete Bearing Under a Base Plate
Inputs
The plate is entered by its width and depth, with the clear distance from each side of the plate to the member edge on that side. A selector chooses whether the bearing areas come from the plate and edges or are entered directly, for example when only part of the plate bears under a moment. The demand is either a compression force, spread evenly over A1, or a peak bearing pressure used as entered.
Bearing areas
Clause 12.6 takes A2 as the largest area of the supporting surface that is geometrically similar to the loaded area A1 and concentric with it. The page scales the plate about its own centre until it first meets a member edge, so the nearer edge in each direction sets a scale and the smaller of the two governs. A plan shows the plate, A2 and the limit beyond which a larger A2 adds nothing.
Bearing strength
The bearing strength rises with the square root of A2 over A1 and is capped, as Clause 12.6 sets out, with the capacity factor for bearing applied. The page compares it with the bearing stress and reports the utilisation with a pass or fail.
Scope
The construction of A2 assumes a rectangular plate on a plane surface with nothing else cutting it, and does not limit A2 by the member thickness below the plate. The plate, the grout, the transfer of force into the member and the anchors are not covered here.
Common Calculation Errors to Avoid
- Taking A2 larger than the edges allow overstates the strength. A2 must be concentric with A1 and geometrically similar to it, so the nearest edge governs.
- Spreading the force over the whole plate under a moment understates the bearing stress. Enter the compression zone area, or the peak pressure under the plate.
- Ignoring the member depth can overstate A2 in a thin member. The page does not check A2 against the thickness below the plate.
- Forgetting bursting and spalling reinforcement leaves the concentrated load unsupported. The clause assumes reinforcement resists those forces.
- Assuming a recess or level change does not matter breaks the plain-surface assumption. Enter A1 and A2 directly in those cases.
Engineering templates
Common calculators
Design guides
FAQs
Why can concrete bear more than its cylinder strength under a plate?
The surrounding concrete confines the loaded area, so the bearing strength rises with the ratio of the supporting area A2 to the loaded area A1, up to the limit AS 3600:2018 Clause 12.6 sets.
How does the page find A2?
It scales the plate about its own centre until it meets the nearest member edge. The smaller of the scales in the two directions governs, so A2 stays concentric with the plate and geometrically similar to it.
When should I enter A1 and A2 myself?
Enter them when only part of the plate bears, such as the compression zone under a moment, or when the supporting surface is not a plain rectangle, for example with a recess, hole or change of level.
Is this an AS 5216 check?
No. Bearing under a base plate is an AS 3600 rule. The page sits with the AS 5216 anchor checks because a base plate in compression bears on the concrete, but the anchors are checked on their own pages.
Does the grout need checking separately?
Yes. The page assumes the plate is flat on the concrete or on a full-strength grout bed, and does not check the grout itself.
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