Caculator for Bolt Preload Tension Force and Equation

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Bolt Preload Tension Force Equation & Calculator

Bolt Preload Tension Force: In the tension joint, the bolt and clamped components of the joint are pre-load designed to transfer the external tension load through the joint by way of the clamped components through the design of a proper balance of joint and bolt stiffness. The joint should be designed such that the clamp load is never overcome by the external tension forces acting to separate the joint (and therefore the joined parts see no relative motion)..

Bolt torque and clamping angle graph

Installed Bolt PreLoad Equations:

F = cAtSp


F = Preload Tension Force
At = Tensile Shear Area of Bolt
Sp = Proof Load of Bolt (or some percentage less than 100% of yield load of bolt, typically 85 % of yield Sy)
c = 0.75 For connections requiring reuse
c = 0.89 For permanent connections

Open --> Bolt Preload Tension Force Calculator

Accuracy of Bolt Preload Based on Bolt Preload Method

Method Accuracy
Torque wrench on unlubricated bolts ± 35%
Torque wrench on cad plated bolts ± 30%
Torque wrench on lubricated bolts ± 25%
Preload indicating washer ± 10%
Strain gauges ± 1%
Computer controlled wrench (below yield) ± 15%
Computer controlled wrench (yield sensing) ± 8%
Bolt elongation ± 5%
Ultrasonic sensing ± 5%