Calculator Inputs
Example Data Table
| Case | Load | Allowable stress | Disp. | γ allow | Layer t | Shape | Typical output |
|---|---|---|---|---|---|---|---|
| A | 900 kN | 10 MPa | 25 mm | 0.70 | 10 mm | Rect (1.5) | ~300×200 mm, ~50–70 mm height |
| B | 600 kN | 8 MPa | 15 mm | 0.60 | 8 mm | Circular | ~310 mm diameter, ~40–60 mm height |
| C | 120 kips | 1500 psi | 0.75 in | 0.70 | 0.40 in | Rect (1.3) | ~9×7 in, ~2–3 in height |
Formula Used
- Plan area: A ≥ P / σ_allow (consistent units).
- Rectangular sizing: W = √(A / r), L = r·W, where r = L/W.
- Circular sizing: D = √(4A/π).
- Shear strain: γ = Δ / T_r, so T_r ≥ Δ / γ_allow.
- Shape factor (approx.): Rectangular S = LW / [2t(L+W)], Circular S = D / (4t).
- Total height (approx.): H = T_r + 2t_cover + (n−1)t_shim.
How to Use This Calculator
- Select a unit system and bearing shape.
- Enter vertical load and allowable compressive stress.
- Enter shear displacement and allowable shear strain.
- Set rubber layer, cover, and shim thickness values.
- Adjust target shape factor range to match your standard.
- Click Calculate to view results above.
- Use the CSV or PDF buttons to export the summary.
Load and Stress Sizing
Bearing plan area is primarily driven by the vertical reaction and the permitted compressive stress of the elastomer compound. The calculator converts load to force and divides by the allowable stress to estimate a minimum plan area. Higher loads or lower allowable stresses grow the plan dimensions quickly, so early load confirmation helps avoid late redesign.
Shear Displacement and Rubber Thickness
Horizontal movement is checked using shear strain, where strain equals displacement divided by total rubber thickness. For example, a 25 mm translation with γallow = 0.70 requires at least 35.7 mm of total rubber. Increasing total rubber thickness reduces strain and usually improves movement capacity, but it may increase overall height.
Shape Factor and Stability
Shape factor is a bulging-control indicator based on loaded area versus free-to-bulge perimeter and layer thickness. Typical target bands often sit around 6 to 12 for laminated bearings, balancing vertical stiffness and shear flexibility. Very low values may increase bulging and compression set, while very high values can make the bearing overly stiff in shear.
Rounding and Standard Sizes
Shop drawings commonly use plan and height increments. The calculator rounds plan dimensions to a chosen step and ensures the adopted area does not fall below the required value after rounding. If rounding reduces area too far, the tool bumps the controlling dimension by one step to restore capacity.
Worked Example
Example inputs: P = 900 kN, σallow = 10 MPa, Δ = 25 mm, γallow = 0.70, layer thickness = 10 mm, L/W = 1.5, cover = 5 mm, shim = 3 mm, plan step = 5 mm. Required area is about 90,000 mm². A practical rounded selection is close to 300 × 200 mm, giving an adopted area of 60,000 mm², so the tool will increase dimensions until adopted area meets or exceeds the required value (often around 370 × 250 mm for this load-stress pairing). Required rubber thickness is 35.7 mm; with 10 mm layers, 4 layers give 40 mm rubber, and the estimated height becomes 40 + 2×5 + 3×3 = 59 mm (before height rounding).
| Input set | P | σallow | Δ | γallow | Typical outcome |
|---|---|---|---|---|---|
| Example | 900 kN | 10 MPa | 25 mm | 0.70 | Plan increases until A ≥ 90,000 mm²; ~4 layers; ~60 mm total height |
FAQs
1) What does “plan area” represent?
It is the loaded footprint of the bearing. The tool sizes plan area so compressive stress stays within your allowable limit for the chosen compound and design basis.
2) Why does rounding sometimes increase my dimensions?
After rounding to practical increments, the adopted area might drop below the required area. The calculator then adds one increment to restore minimum capacity.
3) How is shear movement checked?
Shear strain is computed as displacement divided by total rubber thickness. If the strain exceeds the allowable value, the tool increases total rubber thickness by adding layers.
4) What is shape factor used for here?
It is a quick bulging-control indicator per rubber layer. The calculator reports it and flags when it falls outside your target band, prompting geometry or layer-thickness adjustments.
5) Does the calculator design steel shims?
No. Shim count is estimated as one fewer than the rubber layers, and shim thickness is an input. Final shim detailing should follow your project specification and manufacturer limits.
6) Should I use service loads or factored loads?
Use whichever aligns with your chosen allowable stress basis. Keep the load and stress approach consistent with the same standard, load combination, and safety philosophy.
7) Can I use this output for procurement?
Treat results as preliminary sizing. Confirm rotation, stability, uplift, temperature effects, and code-specific checks with a bearing supplier before finalizing drawings or ordering.