Enter Design Inputs
Formula Used
- Service load: P = DL + LL × (1 + I/100)
- Required area: Areq = (P × 1000) / σallow (MPa = N/mm2)
- Average pressure: σact = (P × 1000) / Aprov
- Shape factor: S = (B × L) / [2 × tlayer × (B + L)]
- Shear strain: γ = Δ / ttotal
These equations provide preliminary sizing checks. Final selection should verify material grade, durability, rotation effects, edge cover, and any code-specific limits.
How to Use This Calculator
- Enter dead and live loads in kN, then set the impact percentage.
- Choose an allowable compressive stress based on your specification.
- Provide total elastomer thickness and layer count for laminated pads.
- Enter expected horizontal displacement and an allowable shear strain.
- Optionally set preferred or maximum plate dimensions for fit.
- Click Calculate to see recommended plan size and checks.
- Download CSV or PDF to attach to design documentation.
Example Data Table
| Case | Service Load (kN) | Allowable Stress (MPa) | Total Thickness (mm) | Suggested Size (mm) | Typical S Range | Comment |
|---|---|---|---|---|---|---|
| A | 500 | 10 | 20 | 225 × 225 | 8–12 | Square pad often suits centered reactions and standard plates. |
| B | 800 | 10 | 25 | 285 × 285 | 8–12 | Increase thickness if movement demand is higher. |
| C | 1200 | 12 | 30 | 320 × 320 | 8–12 | Higher allowable stress reduces required plan area. |
| D | 1500 | 10 | 35 | 390 × 390 | 8–12 | Laminated pads help manage stiffness and bulging. |
| E | 2000 | 10 | 40 | 450 × 450 | 8–12 | May require multiple bearings or larger plate footprint. |
Professional Guide to Elastomeric Bearing Pad Sizing
1) Why bearing pads matter
Elastomeric bearing pads transfer reactions from superstructure to substructure while allowing limited rotation and translation. They reduce stress concentrations at concrete interfaces, accommodate minor construction tolerances, and provide a resilient layer that protects steel and concrete surfaces from local crushing.
2) Key design inputs
Practical sizing starts with service-level reactions. This calculator combines dead load and live load with an impact percentage to form a service load. For bridges and heavy industrial supports, keeping units consistent is essential: kN for load, mm for dimensions, and MPa for stress.
3) Required area and average pressure
The minimum plan area is governed by allowable compressive stress. Using MPa as N/mm2, required area equals load (in N) divided by allowable stress. When the provided area increases, the average pressure decreases, improving durability and reducing long-term creep risk.
4) Shape factor control
Shape factor relates the loaded area to free bulging area for each elastomer layer. Higher shape factor typically increases vertical stiffness and reduces bulging, while very high values can raise stiffness beyond what movement demands need. Many preliminary designs target S between 8 and 12.
5) Thickness and shear strain
Horizontal movement demand creates shear deformation in the elastomer. Shear strain is approximated by displacement divided by total elastomer thickness. Increasing thickness reduces strain, but may affect stability and detailing. A typical preliminary shear strain limit is about 0.5 to 0.7, depending on specification.
6) Plate fit and constructability
Real projects often limit pad footprint to available sole plate size. This calculator lets you cap maximum width and length. If constraints force the pad area below the required area, the tool flags feasibility and suggests relaxing constraints or distributing load across bearings.
7) Typical data ranges for quick checks
Common preliminary compressive stresses are often taken in the 8–12 MPa range for many elastomeric pads, but final values depend on material grade and governing specification. Total elastomer thickness commonly ranges from 15 to 50 mm, depending on movement demands and bearing type. Keep rounding increments practical for fabrication, such as 5 mm.
8) Deliverables and documentation
Engineering workflows benefit from traceable calculations. Use the on-screen result table for review, then export CSV for spreadsheets or generate a PDF for submittals. Record assumptions such as impact percentage, allowable stress source, target shape factor range, and displacement demand, then confirm final bearing selection with suppliers.
FAQs
1) Is this calculator suitable for final design?
It is intended for preliminary sizing and quick checks. Final design should verify code requirements, rotation limits, edge cover, stability, temperature effects, and manufacturer capacity tables.
2) What does the impact percentage do?
The impact value increases the live load portion to reflect dynamic effects. The calculator applies it as LL × (1 + I/100) and adds dead load to form the service load.
3) How should I pick allowable compressive stress?
Use your project specification, applicable standards, and bearing material grade. If uncertain, start with a conservative value and refine after confirming the supplier’s recommended limits.
4) Why is shape factor important?
Shape factor affects bulging and vertical stiffness. Low shape factor increases bulging and strains, while excessively high shape factor can make the bearing too stiff for movement and rotation demands.
5) What if the plate size limits my pad size?
Enter maximum width and length. If the provided area becomes smaller than the required area, the tool flags it. Consider larger plates, multiple bearings, or revising load distribution.
6) How does thickness relate to movement?
Shear strain is approximated as displacement divided by total elastomer thickness. More thickness lowers strain for the same movement, but detailing and stability must still be checked.
7) Does the PDF include my inputs and checks?
Yes. The PDF summarizes key outputs, the full result table, and the notes list. For complete traceability, also download the CSV, which records all inputs and output values.