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Re: Pretensioning Of Anchor Bolts

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Please help me understand the design philosophy of pre-tensioned anchor
bolts.
 
Under an externally applied moment (and axial load) in a column, one or
more anchor bolts will experience tensile stresses.  The actual tensile
stress is then compared with allowable tensile stress.  In pre-tensioned
case, is the bolt subjected to a tensile stress even before external
load acts on the base plate?  I understand that the pre-tension is as
high as 2/3rd of the yield value.  This, in itself, is more than the
allowable stress for the bolt.  So, where does the bolt get its capacity
to resist external moment in addition to bearing the pre-tensile stress?
 
Something is incorrect in my line of thinking, but what is it?  In
post-tensioned concrete, after tensioning the tendons and releasing the
jacks, the tendons tries to get back to its original condition, thereby
introducing compression in concrete.  I have not been into prestressed
concrete after my college course 25 years ago.  But does not the tendon
retain some initial prestress?
 
Rajendran