Inputs
Example data table
These examples illustrate typical input combinations and how utilization changes with bolt count and shear planes.
| Diameter | Strength | Planes | Bolts | Demand | Typical result | Utilization note |
|---|---|---|---|---|---|---|
| 20 mm | 800 MPa | 1 | 4 | 120 kN | Moderate capacity, shear often governs | Improve by adding bolts or double shear |
| 16 mm | 800 MPa | 2 | 6 | 140 kN | Higher capacity due to two planes | Utilization usually drops significantly |
| 3/4 in | 120 ksi | 1 | 2 | 35 kips | Small group, demand may control design | Check bearing when plates are thin |
| 1 in | 120 ksi | 2 | 4 | 80 kips | Robust connection with low utilization | Often governed by geometry, not strength |
Formula used
Shear strength
AISC-style: Nominal per-bolt shear is computed as Rn = C · Fub · A · n, where C depends on threads, A is the selected area, and n is the number of shear planes.
Strength design uses φRn with a typical φ value. Allowable design uses Rn/Ω with a typical Ω value.
Eurocode-style: Design resistance per bolt is computed as Fv,Rd = (αv · fub · A · n) / (γM2 · √3).
Bearing limit (optional)
When enabled, nominal bearing is approximated with Rn = 1.2 · Lc · t · Fu, limited by 2.4 · d · t · Fu. The calculator reports the smaller of shear and bearing as governing.
How to use this calculator
- Select the unit system and the design standard used on your project.
- Enter bolt diameter, ultimate strength, shear planes, and bolt count.
- If threads are in the shear plane, keep the conservative option selected.
- Optionally provide a stress area when threads control shear capacity.
- Enter a demand shear to see utilization for the whole connection.
- Enable the bearing option when plate thickness or edge distance is critical.
- Press calculate to view results above the form, then export if needed.
Use project-specific values and verify drawings before construction.
Bolt shear design notes
Why bolt shear matters on site
Shear connections transfer force through bolts when members slide. Underestimated shear capacity can lead to oversized bolt groups, costly rework, or unsafe detailing. This calculator consolidates key inputs into a clear per-bolt capacity and a total group capacity for practical checks. For preliminary design, engineers often target utilization between 60% and 90% to allow tolerances, erection variability, and future load revisions without redesign on site.
Inputs that drive capacity the most
Capacity is strongly affected by bolt diameter, bolt ultimate strength, and the number of shear planes. Because area scales with diameter squared, small diameter changes can create large capacity shifts. Using consistent units is essential to avoid hidden errors.
Single shear versus double shear
Shear planes represent how many interfaces share the load. A single-shear lap joint typically uses one plane. A double-shear configuration, such as a clevis-style detail, uses two planes and can nearly double the per-bolt nominal shear, subject to governing limits.
Threads and effective shear area
Threads in the shear plane reduce the effective area and often reduce the governing strength. The calculator lets you use a conservative threads-included option or a threaded stress area when you have standard table values. For advanced checks, a custom coefficient is also available.
Bearing can control in thin plates
Even when bolt shear is adequate, the connected plate may fail in bearing. Thin plates, short edge distances, and small clear bearing lengths tend to reduce bearing capacity. The optional bearing check compares shear and bearing and reports the governing mode for safer sizing.
Standards and design philosophies
The calculator supports an AISC-style approach and a Eurocode-style approach. These methods use different safety formats and coefficients, which can change the final design resistance. Select the standard that matches your project requirements and documentation.
Using utilization to size the bolt group
When demand shear is provided, utilization is computed as demand divided by connection capacity. Values near 100% indicate a tight design, while lower values indicate reserve capacity. If utilization is high, increase bolt count, add shear planes, or increase diameter.
Practical tips for reliable results
Confirm bolt grade and material properties from approved submittals. Verify the connection geometry before relying on bearing results, because edge distance and clear length definitions vary across details. Use the CSV or PDF export to attach calculations to RFIs and submittal packages.
FAQs
1) What is the difference between nominal and design strength?
Nominal strength is the base capacity from the equation. Design strength applies the selected safety format, such as a resistance factor or a division factor, to produce a value suitable for checking against demand.
2) When should I use threaded stress area instead of shank area?
Use stress area when threads cross the shear plane or when specifications require it. If the shear plane is through the unthreaded shank, shank area is typically appropriate and may give higher capacity.
3) How do I choose the number of shear planes?
Count the interfaces that resist slip in the direction of the applied shear. Lap joints are usually one plane. Double-shear details, where a plate is sandwiched between two plates, often have two planes.
4) Why might bearing govern even with strong bolts?
Bearing depends on plate thickness, plate strength, and available clear length. Thin plates or short clear lengths reduce bearing resistance, so the plate can deform or tear before the bolt reaches its shear capacity.
5) Does the calculator include slip-critical checks?
No. This tool focuses on bolt shear and an optional bearing limit. Slip-critical design depends on pretension, surface condition, and friction factors, and should be checked with the project’s specified slip-resistant procedure.
6) Should I enter demand per bolt or total demand?
Enter total demand for the connection if bolts share the load. The calculator computes group capacity by multiplying the governing per-bolt strength by the bolt count, then reports utilization using the total demand value.
7) Why do AISC-style and Eurocode-style results differ?
They use different coefficients, partial factors, and formats for converting material strength into a design resistance. Always match the standard used in your drawings and specifications for consistent documentation.
Accurate inputs produce dependable shear checks for every project.