Bearing Load Calculator Formula
Understand the math behind the bearing load calculator. Each variable explained with a worked example.
Formulas Used
Bearing Pressure
bearing_pressure = f_n / bearing_areaVariables
| Variable | Description | Default |
|---|---|---|
force | Applied Force (F)(kN) | 80 |
bearing_area | Bearing Contact Area (A)(mm^2) | 4000 |
f_n | Derived value= force * 1000 | calculated |
How It Works
Bearing Pressure
Bearing pressure is the compressive contact stress between two surfaces, such as a beam sitting on a support plate.
Formula
sigma_b = F / A_bearing
where F is the applied force and A_bearing is the contact area. This must not exceed the allowable bearing stress of the weaker material. For steel on concrete, allowable bearing is typically 0.85 f'c (concrete strength) multiplied by area modification factors.
Worked Example
An 80 kN beam reaction on a 100 mm x 40 mm bearing plate.
- 01Bearing area = 100 x 40 = 4000 mm^2
- 02F = 80 kN = 80,000 N
- 03sigma_b = 80,000 / 4,000 = 20 MPa
Frequently Asked Questions
What is the allowable bearing stress for concrete?
For a bearing plate fully covering the concrete, allowable bearing is typically 0.85 f'c. For smaller plates on larger concrete areas, a confinement factor can increase the capacity by up to a factor of 2.
How do I size a bearing plate?
Divide the reaction force by the allowable bearing stress of the supporting material to get the required bearing area. Then choose plate dimensions that fit the member and support geometry.
Is bearing stress the same as contact stress?
Bearing stress is a simplified average contact stress assuming uniform distribution. True contact stress (Hertzian) accounts for curved surfaces and can have much higher peak values at the centre of contact.
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