KEVOS® MAKEOS · Fasteners
Bolted Joint Load Sharing and Separation
How much of the external load reaches the bolt, and when will the joint separate?
Bolt and member stiffness, joint constant, bolt load, remaining clamp force and separation load of a preloaded tension joint, with an optional frustum estimate of member stiffness.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Nominal diameter | mm | Nominal bolt diameter. |
| Pitch | mm | Thread pitch. |
| Grip length (clamped thickness) | mm | Total thickness of the parts clamped between the bolt head and nut faces. |
| Threaded length within the grip | mm | Length of thread inside the grip (the rest is plain shank). |
| Bolt elastic modulus | GPa | Bolt modulus. |
| Member stiffness | choice | Estimate for plain steel-on-steel plates with washer-face bearing, or enter a value from FEA or tests. |
| Member elastic modulus | GPa | Modulus of the clamped material (for the estimate). |
| Member stiffness (if entered) | kN/mm | Member stiffness from analysis or tests, used when "Enter a value" is chosen. |
| Bolt preload | kN | Installed preload (see the torque and preload tool). |
| External tensile load per bolt | kN | External load trying to separate the joint, per bolt. |
| Proof strength of the bolt | MPa | Proof strength of the bolt property class. |
Method and formulas
- kb = 1 ÷ (Ls ÷ (E Ad) + Lt ÷ (E At)); Ad = πd²/4, At = π/4 (d − 0.938194P)².
- Estimate: km = 0.5774 π E d ÷ (2 ln(5(0.5774 l + 0.5d) ÷ (0.5774 l + 2.5d))).
- C = kb ÷ (kb + km); bolt load Fb = Fi + C P; clamp Fm = Fi − (1 − C) P.
- Separation load P₀ = Fi ÷ (1 − C).
- Example: 35 kN preload with 10 kN external load gives C = 0.19434, a bolt load of 36.943 kN and 26.943 kN left clamping.
Limitations
- Concentric tension joint; prying, bending and thermal loads are not modelled.
- The frustum estimate suits plates of one material with washer-face bearing; gaskets and different materials need a measured or calculated stiffness.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check flange, cap and bracket bolts under external tension
- Find the preload needed to prevent separation
- Compare short and long grip bolts
Who it is for
- Design engineers
- Maintenance fitters
- Quality inspectors
What you get
- Bolt and member stiffness
- Joint constant C
- Bolt load and stress
- Remaining clamp force
- Separation load and load factor
Interpreting the result
- Keep a clear margin against separation; a separated joint transfers the full alternating load to the bolt and loosens.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1521–1535. Topic reference; no source tables or recommended settings are reproduced.
- VDI 2230 Part 1: Systematic calculation of highly stressed bolted joints
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