Results
Enter your connection details and press Calculate. Your result card appears here, above the form.
Calculator
Example data
Use these sample rows to validate your workflow and exports.
| Scenario | Vu (kN) | Tu (kN) | Bolt | Grade | Planes | t (mm) | Fu (MPa) | e (mm) | s (mm) |
|---|---|---|---|---|---|---|---|---|---|
| Light module splice | 60 | 10 | M16 | 8.8 | 1 | 8 | 410 | 35 | 60 |
| Typical frame connection | 120 | 35 | M20 | 8.8 | 1 | 10 | 410 | 40 | 70 |
| Heavier lift-point tie | 220 | 70 | M24 | 10.9 | 2 | 16 | 550 | 55 | 90 |
Formula used
Nominal shear per bolt: RnV = Fnv · Ashear · nplanes
- Fnv = 0.48·Fu when threads are in the shear plane.
- Fnv = 0.62·Fu when threads are excluded.
- Ashear uses At (threads) or Ab (shank).
Nominal tension per bolt: RnT = Fnt · At, where Fnt = 0.75·Fu.
Design/allowable strengths apply factors: LRFD uses ϕ = 0.75. ASD uses Ω = 2.0.
Clear bearing length: Lc = min(e − dh/2, s − dh). Nominal bearing: RnB = 1.2·Lc·t·Fu, capped by 2.4·d·t·Fu.
Final bolt count is the maximum of shear, tension, interaction, and bearing requirements. Interaction uses: n ≥ √[(Vu/Rdv)² + (Tu/Rdt)²].
This tool supports practical preliminary checks. Always confirm with project code, connection type, hole detailing, slip-critical requirements, prying action, and eccentric load effects.
How to use this calculator
- Enter the shear load Vu and tension load Tu.
- Choose bolt size, grade, and whether threads cross the shear plane.
- Set shear planes and hole type to match the connection detail.
- Input plate thickness, material strength, edge distance, and bolt spacing.
- Click Calculate to generate the result card.
- Use CSV/PDF buttons to store results for submittals.
Tip: If bearing governs, increase t, e, or s, or reduce hole clearance where permitted.
Professional notes for module connection bolts
This calculator supports preliminary sizing of bolts used to connect modular frames, corner castings, splice plates, and field-installed brackets. It combines bolt shear, bolt tension, plate bearing, and a simple shear–tension interaction check so designers can quickly compare options and document a repeatable workflow for site connections.
1) Define the demand
Start with factored shear Vu and tension Tu for the connection. Use loads that represent the governing case (transport, lifting, wind, seismic, or handling). Where uplift or prying may be significant, confirm that the connection detail and analysis model capture those effects.
2) Select bolt size and property class
Choose a metric bolt diameter (M12–M30) and property class (4.6–10.9). The tool uses the tensile stress area At for tension and, when threads are in the shear plane, for shear as well. Typical shear coefficients are 0.48·Fu (threads included) and 0.62·Fu (threads excluded), with tension based on 0.75·Fu.
3) Check plate bearing and geometry
Bearing at bolt holes can govern thin plates and large clearances. The calculator estimates hole diameter and uses Lc = min(e − dh/2, s − dh) to compute bearing strength RnB = 1.2·Lc·t·Fu, capped by 2.4·d·t·Fu. If Lc is not positive, increase edge distance, spacing, or reduce clearance.
4) Apply design method and interaction
For LRFD, the tool applies ϕ = 0.75; for ASD it applies Ω = 2.0. Required bolts are computed for shear, tension, bearing, and an interaction relation n ≥ √[(Vu/Rdv)² + (Tu/Rdt)²]. The final count is the maximum of these demands and your minimum bolt requirement.
5) Layout, reporting, and review
A near-square bolt pattern is suggested to simplify erection, with an approximate group size based on edge distance and spacing. Export CSV for traceability and PDF for submittals. Always verify detailing limits, slip-critical needs, corrosion protection, installation torque, and any code-specific factors.
FAQs
1) What loads should I enter for Vu and Tu?
Enter the governing design loads for the connection case you are checking. Use consistent load combinations from your structural analysis and keep units in kN for this form.
2) When should I choose “threads in shear plane”?
If threads cross the shear plane in the actual detail, select “Yes.” If the shear plane passes through the unthreaded shank (e.g., proper grip length), you may select “No” for higher shear resistance.
3) Why does plate bearing sometimes govern?
Thin plates, high hole clearances, and small edge distances reduce the clear bearing length Lc. In these cases, bearing capacity can fall below bolt shear capacity, increasing required bolt count.
4) What does the interaction utilization mean?
It combines shear and tension ratios into one check using a square‑root interaction. Values at or below 1.00 indicate the selected bolt count meets the combined demand for the entered loads.
5) Can I use this for slip‑critical connections?
Not directly. Slip‑critical design depends on faying surface class, pretension, and slip factors. Use this tool for bearing‑type preliminary sizing, then perform a dedicated slip‑critical check if required.
6) How is the suggested layout determined?
The tool proposes a near‑square pattern by choosing columns and rows from the required bolt count. It estimates group dimensions using the entered spacing and edge distance for a quick planning check.
7) What should I do if the status shows CHECK?
Increase bolt count, upgrade bolt class, use double shear where appropriate, or improve detailing (larger thickness, greater edge distance, wider spacing). Then re-run the calculator and confirm the governing requirement is satisfied.