KEVOS® MAKEOS · Fasteners
Friction-Grip (Slip-Resistant) Bolted Joint
Will this preloaded bolted joint carry the shear load by friction without slipping, what tightening torque does that need, and what happens if it does slip?
Check of a friction-grip (slip-resistant) bolted joint in shear: bolt stress area and preload as a share of proof load with the tightening torque (as the bolt torque–preload tool), clamp force left after any applied tension per bolt, slip resistance from the friction coefficient and number of faying surfaces with your slip safety factor, and the bearing-type backup check of bolt shear and plate bearing if the joint slips (as the bolt and pin shear tool).
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Number of bolts | Number of bolts sharing the shear. | |
| Bolt diameter | mm | Nominal bolt diameter. |
| Thread pitch | mm | Thread pitch. |
| Bolt proof strength | MPa | Proof strength of the bolt grade (for example about 600 MPa for 8.8, 830 for 10.9). |
| Preload as share of proof load | % | Preload as a share of the proof load. |
| Nut factor | Nut factor for the thread condition (about 0.2 dry steel, 0.15 lubricated). | |
| Slip (friction) coefficient | Slip coefficient of the prepared faying surfaces (your value from the surface class). | |
| Faying surfaces (slip planes) | Number of contact surfaces the shear crosses (1 for a lap joint, 2 for a double cover plate). | |
| Slip safety factor | Factor you require against slip. | |
| Shear load on the joint | kN | Shear force on the whole joint. |
| Applied tension per bolt | kN | External tension per bolt, which reduces clamp force. |
| Thinnest plate (for bearing) | mm | Thinnest plate the bolts bear on if the joint slips. |
| Allowable bolt shear stress | MPa | Allowable shear stress of the bolt for the bearing-type backup. |
| Allowable bearing stress | MPa | Allowable bearing stress of the plate. |
Method and formulas
- Stress area A_s = π ÷ 4 (d − 0.9382P)²; preload F_p = share × S_p A_s; torque T = K F_p d (as the bolt torque–preload tool).
- Clamp left per bolt = F_p − F_t (applied tension taken fully off the clamp, conservative).
- Slip resistance = n × planes × μ × clamp ÷ slip factor.
- Backup: bolt shear τ = V ÷ (n × planes × π d² ÷ 4); bearing σ = V ÷ (n d t) (as the bolt and pin shear tool).
- Example: 4 M16 bolts at 75% proof clamp 70.501 kN each and resist 67.681 kN against 40 kN; torque 225.6 N·m.
Limitations
- Nut factor scatter makes torque-controlled preload uncertain by ±25% or more.
- Structural friction-grip joints must follow the steel code for bolt grade, surface class and inspection.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Design a slip-resistant splice or bracket connection
- Check a joint that must not move under reversing loads
- Find the tightening torque for the clamp needed
Who it is for
- Structural engineers
- Design engineers
- Maintenance engineers
What you get
- Preload and tightening torque
- Slip resistance against the shear load
- Bearing-type backup if slip occurs
Interpreting the result
- Surface preparation sets the slip coefficient: blasted, unpainted surfaces grip far better than painted ones.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1521–1535, 1720–1735. Topic reference; no source tables or recommended settings are reproduced.
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Open the Friction-Grip (Slip-Resistant) Bolted Joint calculator
