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RE: A325 bolts - nuts not fully engaging threads

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I may be wrong, but I think the 2 thread beyond the bolt comes from an ASME specification such as for bolted pipe flanges.

Thomas Hunt, S.E.

"Carter, Charlie" <carter(--nospam--at)>
04/27/2006 12:53 PM
Please respond to seaint
RE: A325 bolts - nuts not fully engaging threads

No, but it is a pervasive wives’ tale. The nut size already accounts for the taper to make it all as easy as could be.

From: Michel Blangy [mailto:mblangy(--nospam--at)]
Thursday, April 27, 2006 2:44 PM
RE: A325 bolts - nuts not fully engaging threads

I was taught to look for two threads beyond the nut since the first couple are slightly tapered. Is this in any spec.?
Michel Blangy
-----Original Message-----
Carter, Charlie [mailto:carter(--nospam--at)]
Thursday, April 27, 2006 9:07 AM
RE: A325 bolts - nuts not fully engaging threads

The height of the nut is selected to develop the strength of the bolt, but that presumes the point of the bolt is st least flush with the surface of the nut. Since the various methods of pretensioning A325 and A490 bolts actually elongates the bolt slightly, I suspect you will some thread stripping during installation with partially engaged nuts.
Even if you didn’t strip threads during installation, the strength calculations for partial engagement can be complex. The strength in tension may now be controlled by the stripping mechanism, which is a much more variable mechanism than bolt tension failure. The shear strength of the bolt is unaffected, but it still seems like a bad practice to allow improperly selected components. I’d suggest that they go buy bolts of the right length.
How did they wind up with short bolts anyway?



From: Haan, Scott M POA [mailto:Scott.M.Haan(--nospam--at)]
Thursday, April 27, 2006 10:43 AM
A325 bolts - nuts not fully engaging threads


I had a question posed to me about a project using A325 bolts where the threads are not being fully engaged at some of the joints.  This is apparently occurring at some brace connections [designed under old building code] that are required to be fully pre-tensioned because they are resisting seismic forces and at beam connections that are allowed to be bearing connections.

I know the RCSC spec says bolts are supposed to be long enough fully engage the nuts but what are the strength issues involved with having bolts to short to fully engage nuts for: direction tension connections, connections that resist seismic forces in shear, bearing shear plate connections?

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