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RE: Bolt Tension

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The high bolt pretension force assures that the bolt will be loaded at the time of installation to such a level as to provide a clamping action in the assemblage.  After the bolts in a connection are fully tensioned and the whole connection is loaded from zero to the design load level, the bolts will have no increase or decrease in stress.  The only way to induce a change of stress in the bolt is to exceed the design load of the connection.  With no variation in the stress in the preloaded bolt, there is no cyclic loading or fatigue in the bolt.

The high pretension force also means that if the bolt is not of good quality, it will generally break during the installation process.  That is why the counterfeit bolt problem of the late 80's early 90's was not too big of a problem in A325 bolts.  Essentially each bolt is tested when it is installed.  Counterfeit bolts were a problem with the Grade 5 bolts where bolt pretension is not mandated and failures occurred after design loads were applied.

I realize that the engineer can wave tensioning A325 bolts.  That should only be done in rare cases.

Harold Sprague
Krawinkler, Luth & Assoc.




-----Original Message-----
From:	Alex Nacionales [SMTP:anacio(--nospam--at)skyinet.net]
Sent:	Tuesday, April 28, 1998 3:20 AM
To:	seaoc(--nospam--at)seaoc.org
Subject:	Bolt Tension

Hello all.
There is something I do not understand in the AISC manual.
The required minimum bolt tension to fasten bolts is much larger than the allowable tension load of the bolts.
Maybe you guys can help.
Thanks in Advance.
Alex Nacionales, C.E.
anacio(--nospam--at)skyinet.net


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