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RE: [StrucTX] Grade 8 Bolts

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Title: RE: [StrucTX] Grade 8 Bolts

From AISC's A Guide to Engineering and Quality Criteria: Common Questions Answered,

"6.2.5. Is it acceptable to substitute SAE J429 grades 5 and 8 bolts for ASTM A325 and A490 bolts, respectively?

No. The strength properties of SAE J429 grade 5 bolts and ASTM A325 bolts are identical; likewise, SAE J429 grade 8 bolts are the strength equivalent of ASTM A490 bolts. These material specifications differ, however, in that ASTM A325 and A490 specify thread length and head size, whereas SAE J429 does not. Additionally, quality assurance and inspection requirements for ASTM A325 and A490 bolts are more stringent."

Since AISC and RCSC specifications call for pretensioned installation for your application (which involves fatigue), I would question whether the SAE fasteners that were installed were properly installed. Also, I'd question if the head size, threading and quality assurance were adequate for the application.

Usually, the request to substitute an SAE fastener for A325 or A490 comes because SAE's are cheaper. Perhaps that gives you the answer right there.

Charlie

-----Original Message-----
From: fconner(--nospam--at)pcola.gulf.net [mailto:fconner(--nospam--at)pcola.gulf.net]
Sent: Friday, February 25, 2000 10:02 AM
To: seaint(--nospam--at)seaint.org
Cc: StructTX
Subject: [StrucTX] Grade 8 Bolts


I have an long-time industrial client who recently replaced a bunch of
*missing* structural bolts with "Grade 8" (I assume SAE, Grade 8) bolts.  I
can only guess what happened to the original bolts.  I'm sure they weren't
stolen, so that leaves the options of working loose or breaking under
repetitive load cycles -- This is a vertical bolt, attaching a crane girder
to a column cap plate.  Can anyone say, "fatigue"?

I'm not comfortable with this replacement.  So far as I can tell, the grade
8 machine bolt is hard, tough, and *brittle*.  'Sounds like courting
disaster to me...

I recommended replacing the *new* bolts with A325, but the client is
reluctant to spend money twice for the same work. 

Guidance and counsel, anyone? 

Fountain E. Conner, P.E.
Gulf Breeze, Fl. 32561

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