Input Data
Example Data Table
| Case | Bolt Size | Area (mm²) | Proof Strength (MPa) | External Tension (N) | External Shear (N) | Bolts |
|---|---|---|---|---|---|---|
| Machine base | M12 x 1.75 | 84.3 | 600 | 18000 | 6000 | 4 |
| Steel bracket | M16 x 2 | 157.0 | 600 | 40000 | 18000 | 4 |
| Drive housing | M20 x 2.5 | 245.0 | 830 | 65000 | 28000 | 6 |
Formula Used
Tensile stress area: At = π/4 × (d − 0.9382p)² for standard metric threads when no direct area is entered.
Proof load: Fp = At × Sp
Preload: Fi = preload factor × Fp
Added bolt tension from service load: ΔFb = C × (Ft / n)
Total bolt tension: Fb = Fi + ΔFb
Shear per bolt: Fv,b = Fv / n
Tensile stress: σ = Fb / At
Shear stress: τ = Fv,b / At
Allowable shear stress: τallow = ks × Su / safety factor
Von Mises stress: σe = √(σ² + 3τ²)
Interaction ratio: (σ / σallow)² + (τ / τallow)²
These expressions provide a practical engineering check for preload, axial demand, shear demand, slip resistance, and combined stress behavior.
How to Use This Calculator
- Enter the bolt diameter, pitch, and material strengths.
- Type the tensile area if you already know the exact value.
- Set preload factor and joint stiffness factor for the assembly.
- Add total external tensile and shear loads on the joint.
- Enter the number of bolts sharing the service load.
- Choose friction coefficient and your target safety factor.
- Press Calculate Strength to show results above the form.
- Download the result summary as CSV or use print-to-PDF.
Frequently Asked Questions
1. What does this calculator check?
It estimates bolt proof load, preload, tensile stress, shear stress, combined stress, slip resistance, and utilization. That helps you compare service demand against selected material limits.
2. Can I use a known tensile stress area?
Yes. If you already have the published tensile stress area for a bolt size, enter it directly. The calculator will then skip the geometric approximation.
3. What is the joint stiffness factor?
It represents the share of external tensile load transferred into the bolt. A higher value means the bolt takes more of the service tension.
4. Why is preload important?
Preload creates clamp force, improves fatigue behavior, and can resist transverse shear by friction. Too little preload reduces joint security, while too much risks proof overload.
5. How is shear strength handled?
The tool uses a shear strength factor multiplied by ultimate strength, then divides by the safety factor. This gives a practical allowable shear stress for design screening.
6. What does the interaction ratio mean?
It combines tensile and shear demand into one indicator. Values at or below one generally indicate the selected allowable limits are not exceeded.
7. Is this suitable for code compliance?
Use it for preliminary engineering checks and comparisons. Final designs should still follow the governing standard, manufacturer data, and project-specific assumptions.
8. How do I save the output as a PDF?
Click the PDF button. It opens the browser print flow, where you can choose Save as PDF. That keeps the visible result section and reference content.