Theory of High Strength Bolting

The principle of slip-critical connections relies upon tensioning each bolt in the connection to a specified minimum tension so that the desired clamping force will be induced in the connection interface. Shear loads are then transferred by frictional resistance in the joint interface rather than by bearing on the bolt shanks and hole faces. In this type of connection, there will be no movement of the connected materials when the connection is subjected to these loads. Movement in many types of joints is highly undesirable, hence the development of the slip-critical connection.

When tension loads are applied in the direction of the bolt axis, tensioning to a specified minimum tension is also important, particularly if the loads are cyclical and could induce loosening or fatigue failure of the bolts. The clamping force at the specified minimum tension should be significantly greater than the applied loads. This will prevent the plies from separating or the bolts from developing an increase in tension stress over the installed pretension stress.