Formula Used
Direct bolt shear stress
τ = V ÷ (n × m × Ae)
V is design shear force, n is bolt count, m is shear planes, and Ae is effective area.
Gross shank area
A = πd² ÷ 4
Von Mises combined stress
σv = √(σ² + 3τ²)
How to Use This Calculator
- Select direct, sizing, combined, or eccentric analysis.
- Choose consistent force, length, and stress units.
- Enter the applied loads and number of shear planes.
- Select the bolt area method and material strength basis.
- Enable supplementary plate checks when useful.
- Review the status, utilization, capacity, and warnings.
Example Data
| Example | Load | Bolts | Planes | Diameter | Area choice |
|---|---|---|---|---|---|
| Single-shear lap joint | 50 kN | 4 | 1 | 12 mm | Shank |
| Double-shear clevis | 80 kN | 2 | 2 | 16 mm | Shank |
| Threads in shear plane | 35 kN | 3 | 1 | M12 × 1.75 | Tensile area |
| Eccentric bracket | 30 kN, 40 kN, 5 kN·m | 4 | 1 | 16 mm | Shank |
Engineering Guidance
Bolt shear calculations estimate how an applied transverse force is resisted by one or more fasteners. The basic method assumes each bolt shares load according to the selected distribution factor. Real joints may behave differently because of clearance, fit, stiffness, pretension, deformation, and installation tolerance.
Use the full shank area when the smooth bolt body crosses every shear plane. Select a threaded area when threads cross a plane because the effective diameter is smaller. A custom area can represent manufacturer data, unusual threads, reduced sections, or project-specific design values.
Single shear occurs when one interface cuts across a bolt. Double shear occurs when two interfaces resist the same bolt load, as in many clevis arrangements. More planes increase total resisting area, but plate behavior and load transfer still require independent checks.
Allowable stress can be entered directly or estimated from yield or ultimate strength. The shear-to-tensile ratio, resistance factor, material factor, and safety factor must match the intended design method. Do not mix allowable-stress and resistance-factor formats without a justified engineering basis.
Combined loading adds axial stress to bolt shear. This calculator reports a Von Mises equivalent stress for ductile behavior. Prying, bending, thread stripping, fatigue, preload loss, and fluctuating loads are not fully represented by that single interaction result.
Eccentric analysis uses bolt coordinates to calculate the group centroid and moment distribution. Direct force and moment-induced force are vector-added at each bolt. The most heavily loaded bolt becomes the governing fastener for the displayed group check.
Supplementary bearing, tear-out, net-section, and slip calculations are screening estimates. Applicable structural, mechanical, aerospace, automotive, pressure-vessel, or equipment standards may define different equations and resistance factors. Final selections should be reviewed by a qualified engineer familiar with the governing code.
Frequently Asked Questions
What is bolt shear stress?
It is transverse force divided by the effective resisting bolt area across the active shear planes.
What is the difference between single and double shear?
Single shear has one resisting plane per bolt. Double shear has two resisting planes and usually doubles ideal bolt shear area.
Should threads be included in the shear plane?
Prefer excluding threads when practical. When threads cross the plane, use an appropriate reduced effective area.
How is required bolt diameter calculated?
The direct shear equation is rearranged to find the area and diameter needed for the design load and allowable stress.
How is required bolt count rounded?
The calculated quantity is rounded upward because a partial bolt cannot provide dependable design resistance.
What does utilization mean?
Utilization is demand divided by allowable capacity. A value at or below one passes the selected criterion.
Can this calculator analyze an eccentric bracket?
Yes. Enter bolt coordinates, force components, and a moment or eccentricity to calculate individual resultant bolt forces.
Does the calculator replace structural design codes?
No. It is a general engineering aid and does not replace code-specific checks, detailing, or professional review.
Why might plate failure govern first?
Thin plates, small edge distances, large holes, or weak materials can fail in bearing, tear-out, or net tension before bolt shear.