Tutorial on the Basics of Bolted Joints

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The Effect of a Compressive External Force

If the joint experinces a compressive external force this has the effect of increasing the clamp force acting on the joint and decreasing the tension in the bolt. This is illustrated with the joint diagram shown below. If the compressive external force is great enough then either:

1. The tension in the bolt can be reduced to a low value - if the external load is cyclic then the bolt could fail due to fatgue (since it is experiencing tension variations under a compressive external force). Also the bolt is more susceptable to vibrational loosening.

2. The yield limitations of the clamped material may be exceeded since the joint is sustaining a compressive force in addition to that provided by the bolt's preload. This will result in some permanent deformation that upon the release of the external force a loss of bolt preload would result.

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