Enter Bolt And Load Data
Formula Used
Direct bolt tension: Td = (P ÷ n) × Kd.
Eccentric bolt tension: Tm = M × ymax ÷ Σy². Metric moment is converted from kN·m to kN·mm.
Critical service tension: Ts = Td + Tm.
Design tension: Tu = Ts × load factor.
Tensile stress: ft = Tu ÷ Ab.
Design capacity: Rd = φ × Ab × Fselected.
Utilization: U = Tu ÷ Rd. Values above 1.00 need revision.
Pretension: Fp = Ab × proof stress × pretension percentage.
Torque estimate: Torque = K × Fp × d.
How To Use This Calculator
- Select metric or inch-pound units before entering data.
- Enter the total axial load acting on the bolt group.
- Add the number of bolts that actually share the tension.
- Use the distribution factor for uneven load sharing.
- Enter eccentric moment data when the load is off center.
- Select the bolt area basis and material stress basis.
- Press the calculate button to review demand, capacity, and utilization.
- Download the result table or print the page as a PDF record.
Example Data Table
| Case | Load | Bolts | Diameter | Moment | Use |
|---|---|---|---|---|---|
| Small bracket | 40 kN | 4 | M16 | 2 kN·m | Light support review |
| Base plate | 120 kN | 4 | M20 | 8 kN·m | Anchor tension check |
| Hanger connection | 18,000 lb | 6 | 0.75 in | 12,000 lb·in | Steel framing review |
Design Notes for Bolt Axial Loading
Why Axial Load Matters
Bolts in tension carry force along their shank. This force can come from hanger rods, base plates, splice plates, bracing, or uplift anchors. A small error can change the stress ratio fast. Axial checks also affect joint stiffness. They help decide bolt size, grade, washer type, and pretension level.
What The Calculator Checks
This tool estimates direct tension, eccentric tension, design load, tensile stress, and capacity. It also estimates pretension and torque. The moment option is useful for bracket groups and anchor groups. It uses the farthest bolt distance and the sum of squared distances. That gives a practical critical bolt estimate.
Inputs That Need Care
Use the real bolt count that shares the force. Do not include bolts outside the active tension group. Enter the tensile stress area when threads are in the shear plane or tension path. Use shank area only when the unthreaded body controls. Grade stresses must match the selected unit system. Metric stresses are in MPa. Inch based stresses are in psi.
Reading The Result
The utilization ratio is the main review number. A value below one means the calculated design demand is below design capacity. A higher value means the selected bolt is overstressed. The safety factor gives another quick check. It compares available capacity against the calculated demand. The stress output helps compare against material limits.
Construction Use
This calculator is best for early design, estimating, and field review. It supports quick checks before a detailed connection model is made. It can also compare bolt grades and diameters quickly. For critical structures, verify edge distance, spacing, prying action, slip, fatigue, corrosion, and code rules. Anchors may need concrete breakout checks. Timber and masonry connections need separate material checks.
Good Practice
Keep units consistent. Use conservative load factors when the load path is uncertain. Include eccentricity when the load is not centered. Check the most loaded bolt, not the average bolt only. Use certified bolt data for final work. Ask a licensed engineer to review life safety connections.
Limits To Remember
Results depend on entered assumptions. They do not replace a connection specification. Bolts may fail by thread stripping, bearing, tear out, pullout, or bending. These modes need separate checks. Review before final approval.
FAQs
What is bolt axial load?
Bolt axial load is tension acting along the bolt centerline. It stretches the bolt. It can come from direct pull, uplift, hanger force, or eccentric connection action.
What does utilization mean?
Utilization compares design tension with design capacity. A value of 0.80 means the bolt uses 80 percent of calculated capacity. A value above 1.00 needs revision.
Should I use tensile area or shank area?
Use tensile stress area when the threaded part controls tension. Use shank area only when the unthreaded body is the controlling tension section.
How is eccentric moment included?
The calculator adds moment tension using the farthest bolt distance and the sum of squared bolt distances. This estimates the most loaded bolt in the group.
What is the distribution factor?
The distribution factor adjusts for uneven load sharing. Use 1.00 for equal sharing. Use a higher value when geometry, stiffness, or fit-up causes unequal tension.
What resistance factor should I enter?
Use the factor required by your design method, material, and local code. Common preliminary values are below 1.00. Final values need project verification.
Can this calculator size anchor bolts?
It can estimate steel tension in anchor bolts. It does not check concrete breakout, pullout, pryout, edge distance, cracked concrete, or adhesive capacity.
Does the torque result guarantee preload?
No. Torque is only an estimate. Lubrication, coating, thread condition, washers, and installation method can change actual pretension significantly.
Can I use inch-pound units?
Yes. Select inch-pound units. Enter load in pounds, moment in pound-inches, lengths in inches, area in square inches, and stresses in psi.
Why is my safety factor low?
A low safety factor usually means high load, small bolt area, weak material stress, large eccentricity, or a conservative resistance factor. Check each input carefully.
Is this enough for final design?
No. Use it for estimating and review. Final design should check applicable codes, connection geometry, prying, fatigue, slip, bearing, and material-specific limits.