How to use this calculator
- Enter total load. Use the shear or bearing load carried by this group.
- Enter fastener count. Use the number of bolts or pins sharing the load.
- Enter diameter and thickness. Use the bearing diameter and the plate thickness being checked.
- Set allowable stress. Enter the material bearing limit and desired safety factor.
- Read utilization. A utilization below 1 means the average bearing stress is below the design allowable.
How it works
A bolt or pin bearing against a hole creates a curved local contact stress. For
practical average bearing checks, the curved patch is replaced by the projected
area:
A_b = d x t
Load per fastener is F_bolt = F / n.
The average bearing stress is sigma_b = F_bolt / A_b. The calculator
compares it with sigma_allow / safety factor, then back-solves the
required thickness and required diameter if you hold the other dimension fixed.
Worked example
Verified against the live calculator
A 10,000 N joint load shared by 2 bolts puts
5,000 N on each bolt. A 10 mm bolt in a
6 mm plate has projected bearing area 60 mm^2.
Bearing stress is 5000 / 60 = 83.33 MPa. With
250 MPa allowable and safety factor 2, design bearing
stress is 125 MPa, so utilization is 0.667.
Frequently asked questions
How do you calculate bearing stress in a bolted plate?
Average bearing stress is load per fastener divided by projected bearing area: sigma_b = F_bolt / (d * t), where d is bolt or pin diameter and t is plate thickness.
What is projected bearing area?
Projected bearing area is the rectangular projection of the curved contact patch, usually bolt or pin diameter times plate thickness, A_b = d * t.
Does the calculator divide the load across bolts?
Yes. It divides the total entered load equally by the entered fastener count. For eccentric groups, calculate the worst bolt load first with a bolt-pattern force method.
What allowable stress should I use?
Use a material or code-based allowable bearing stress for the plate or lug material, then apply the safety factor you want for the design check.
Does this check tear-out or net-section failure?
No. Bearing is only one limit state. You still need checks for bolt shear, bolt tension, plate tear-out, net-section tension, edge distance, fatigue and any governing design code.
Does it work for pins as well as bolts?
Yes for the average projected bearing stress check. Pin bending, lug geometry and double-shear load split may need additional calculations.
Method & assumptions
- Average projected-area bearing stress:
sigma_b = F_bolt / (d x t). - Total load is split equally across the entered fastener count.
- Allowable comparison uses entered allowable stress divided by entered safety factor.
- Bolt shear, bolt tension, plate tear-out, edge distance, net-section tension, prying, fatigue and code-specific resistance factors are not checked.