Formula Used
Thread shear pull out: F = π × de × Le × τ × Kt × R
Bond pull out: F = π × d × Lembed × b × R
Cone breakout: F = Acone × σt × R
Pull through: F = Awasher × σt × R
Bolt tensile limit: F = At × σbolt
Working load: Working Load = Governing Ultimate Load ÷ Safety Factor
Here, R equals installation factor × edge factor × spacing factor.
The calculator uses the lowest selected capacity as the governing result.
How To Use This Calculator
Choose the unit system first. Enter bolt diameter, engagement length, embedment depth, and material strengths. Add reduction factors for edge distance, spacing, and installation quality. Select one failure mode or compare all modes. Press the calculate button. Review the governing capacity, working load, and utilization ratio.
Example Data Table
| Example |
Bolt diameter |
Engagement |
Embedment |
Shear strength |
Bond strength |
Safety factor |
| Mild steel tapped plate |
10 mm |
20 mm |
40 mm |
140 MPa |
5 MPa |
3 |
| Concrete adhesive anchor |
12 mm |
30 mm |
90 mm |
100 MPa |
8 MPa |
4 |
| Soft aluminum thread |
8 mm |
16 mm |
30 mm |
70 MPa |
4 MPa |
3.5 |
Bolt Pull Out Force Basics
A bolt pull out force calculator estimates the axial load that may pull a fastener from its base material. It is useful for tapped holes, anchors, inserts, studs, and embedded bolts. The result is not one universal number. Several failure modes can control the design.
The calculator compares thread shear, bond failure, cone breakout, and pull through. It also estimates bolt tensile capacity. The smallest capacity is normally the governing value. This conservative view helps users see the weakest part of the connection.
Important Inputs
Diameter controls contact area. Engagement length controls how much material resists pull out. Shear strength or bond strength describes the resistance of the receiving material. Tensile strength describes the bolt itself. Edge factor, spacing factor, and condition factor reduce capacity when the installation is not ideal.
Use consistent units. Millimeters and MPa work together because one MPa equals one newton per square millimeter. Inches and psi also work together, but the calculator converts them to SI values internally. This keeps the formulas stable.
Why Safety Factor Matters
A calculated ultimate load is not the same as a safe working load. Real anchors face vibration, corrosion, misalignment, poor drilling, weak concrete, and temperature changes. A safety factor reduces the ultimate value to a working load. Higher factors are usually better for uncertain materials or critical loads.
Practical Design Notes
Thread pull out is common in soft materials. Aluminum, plastic, wood inserts, and weak castings need careful engagement length. Bond pull out often applies to adhesive anchors. Cone breakout can control concrete or masonry anchors. Pull through can control thin plates or washers.
Always inspect the actual installation. Verify embedment, hole size, thread condition, material grade, and tightening method. This calculator is a planning tool. Final designs should follow project codes, manufacturer data, and qualified engineering review. When values look close, increase engagement, use a larger washer, choose a stronger insert, or reduce the applied load.
Reading The Output
The result panel shows each capacity, the governing limit, and the working load. It also reports utilization when an applied load is entered. A utilization below one is acceptable for the chosen factor. A value above one needs changes or approval before installation.
FAQs
What is bolt pull out force?
It is the axial force needed to pull a bolt, anchor, or insert from its base material. It depends on diameter, engagement, embedment, material strength, and failure mode.
Which failure mode should I select?
Use compare all modes when unsure. Select one mode only when you know the connection is controlled by thread shear, adhesive bond, cone breakout, pull through, or bolt tension.
Why is the lowest result used?
The connection usually fails at its weakest limit. Using the smallest calculated capacity gives a conservative governing value for design checks and safety review.
What is thread engagement length?
It is the length of thread contact between the bolt and receiving material. Longer engagement usually raises pull out resistance until another failure mode controls.
What safety factor should I use?
Common checks use values from 2 to 5. Use higher values for uncertain materials, critical loads, vibration, poor installation, or outdoor exposure.
Can this calculator replace manufacturer data?
No. Manufacturer anchor tables and project codes should control final design. This calculator is useful for planning, comparison, and early engineering checks.
Why enter edge and spacing factors?
Close edges and nearby anchors can reduce capacity. These factors let you reduce the estimate when the installation has limited surrounding material.
Does it work for concrete anchors?
It gives a simplified cone and bond estimate. Concrete anchor design can require code equations, cracked concrete checks, seismic factors, and approved product data.