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RE: seaint Digest for 22 Jul 1998

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I've spent too much time on this, but I guess I just don't want to get back
to work.

There appears to be a misconception regarding the clamping stresses in bolts
in tension in connections. It has been asserted that applied loads to the
connection will relieve some of the stresses on bolts, loads up to the point
where clamping stress equals stress due to applied loads. 

My own understanding is that the only way to relieve tension stress in the
bolt is to remove the strain in it...in other words, let the bolt shorten to
its original length. As the tension load is applied to the bolt through the
connected parts, the bolt is not going to  get shorter (thereby relieving
strain) but get stretched even more. As the bolt stretches more, it is under
still more stress, a stress in proportion to its dimensions and the applied
force.

An analogy in prestressed concrete is in the tendons. The tendons are
prestressed. When a load is applied to the beam, the stress goes up in the
tendon, not down. Fine, the tendons take advantage of steel's high strength
and ductility. HS bolts are used in the same way. They have a higher
capacity for loads in real connections than what one would determin from
just P/(A x Fu).

Ted