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Re: Anchor Bolts in Fatigue

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On Aug 28, 2007, at 4:21 PM, Daryl Richardson wrote:

The force in the anchor bolt is equal to the GREATER of the pretension OR the applied bolt load. If the pretension is 125% of the fatigue loading it should never change, hence, zero stress range, hence zero fatigue (unless I'm misunderstanding your description of the problem).
This assumes that the bolt is a lot softer (compliant soft, not brinnell soft) than the contact compliance of the parts being clamped together. This is usually true for bolted joints steel, but maybe not for anchor bolts embedded in concrete. What actually happens in that case is that the change in applied loading nearly equals the change in contact force so the bolt tension doesn't change much. So a cyclic applied load doesn't cycle the bolt load, provided the two halves of the joint remain in contact.

You might want to check your joint design compliances to make sure the relative stiffness is such that the bolt load doesn't cycle. There's a good explanation of all this in machine design handbooks and the arithmetic isn't difficult. If you're really intending to do this, you might also want to make provisions that mimic the installation of preloaded high strength bolting in ordinary structural joints.

Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw(--nospam--at)skypoint.com   | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw/



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