Bolt Tensile Input Form
The page stays single-column overall, while the input area uses 3 columns on large screens, 2 on smaller screens, and 1 on mobile.
Example Data Table
This worked example uses the default values prefilled in the form.
| Parameter | Symbol | Example Value | Unit |
|---|---|---|---|
| Bolt designation | - | M20 | - |
| Nominal diameter | d | 20 | mm |
| Thread pitch | p | 2.5 | mm |
| Number of bolts | n | 4 | count |
| Ultimate tensile strength | Fu | 800 | MPa |
| Yield strength | Fy | 640 | MPa |
| Proof strength | Sp | 600 | MPa |
| Preload ratio | α | 0.75 | - |
| Joint stiffness factor | C | 0.25 | - |
| Distribution factor | λ | 1.10 | - |
| Total external tensile load | P | 140 | kN |
| Safety factor | Ω | 1.50 | - |
| Tensile stress area | At | 244.794 | mm² |
| Proof load per bolt | Fp | 146.876 | kN |
| Peak bolt tension | Fmax | 119.782 | kN |
| Proof utilization | Uproof | 81.55 | % |
Formula Used
This calculator uses a practical metric-thread tensile model for quick connection review.
At = (π / 4) × (d − 0.9382p)2
Fp = At × Sp / 1000
Fy,load = At × Fy / 1000
Fu,load = At × Fu / 1000
Fi = preload ratio × Fp
Pbolt = (P / n) × λ
ΔFb = C × Pbolt
Fmax = Fi + ΔFb
Psep,total = [Fi / (1 − C)] × n / λ
nreq = ceil[(P × λ × C) / ((Fp − Fi) / Ω)]
How to Use This Calculator
- Enter the bolt designation for reference, such as M16 or M20.
- Provide the nominal diameter and thread pitch in millimeters.
- Enter the number of bolts resisting the applied tensile force.
- Fill in the bolt material properties: ultimate, yield, and proof strengths.
- Choose a preload ratio. A common estimate is 0.70 to 0.80.
- Enter the joint stiffness factor C to represent how much external load transfers into the bolt.
- Add a distribution factor λ if eccentricity, uneven sharing, or uncertainty increases demand.
- Enter the total external tensile load and the target safety factor.
- Press the calculate button. The result will appear below the header and above the form.
- Review stress area, tension checks, separation threshold, and required bolt count.
- Use the CSV and PDF buttons to download a calculation summary.
FAQs
1) What is tensile stress area in a threaded bolt?
Tensile stress area is the effective resisting area at the threaded section. It is smaller than the shank area because the thread root reduces the metal available to carry tension.
2) Why does this calculator use proof strength?
Proof strength is useful for preloaded bolts because it reflects the load that can be sustained without permanent set. It gives a practical limit for preload-based service checks.
3) What does the preload ratio control?
The preload ratio scales the initial clamp force as a fraction of proof load. Higher preload can improve joint clamping, but it also consumes more of the bolt’s tensile reserve.
4) What is the joint stiffness factor C?
C represents how much external tensile load goes into the bolt instead of unloading the clamped parts. Lower values mean the joint absorbs more load before bolt tension rises.
5) Why is there a distribution factor λ?
The distribution factor increases the nominal per-bolt load to reflect uneven sharing, eccentricity, fabrication tolerance, or simplified load path assumptions in real construction connections.
6) Can I use inch-based bolts with this page?
Yes, but first convert diameter and pitch into millimeters and use strengths in MPa. Keeping all units consistent is essential for reliable output.
7) Why does the required bolt count sometimes jump sharply?
It rises when preload is high, proof reserve becomes small, or the joint factor and distribution factor increase. These inputs reduce the extra load each bolt can safely accept.
8) Does this calculator replace detailed code-based connection design?
No. It is best for preliminary evaluation, comparison, and education. Final design should still confirm applicable standards, prying action, fatigue, slip behavior, and detailing requirements.