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RE: Washers for A490 Bolts

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Title: RE: Washers for A490 Bolts

>On one of our projects,  1-1/2" dia. A490N bolts were specified for shear
>tab beam connection.  Because of fit-up, the contractor made the connection
>using short slotted holes in the beam web.  However, the requirements for
>minimum 5/16" thick washers were overlooked.  The beam is in place now and
>because of the existing conditions, the connection can not be accessed to
>replace the bolts and the washers. What is the reason for requiring 5/16 inch
>washers?

Thicker washers are required for pretensioned applications with A490s of diameter greater than 1 in.because of the tendency of standard F436 washers to dish into the hole, thereby reducing the clamping force induced using an otherwise acceptable installation procedure.

>Can one use some reduced capacity when standard thickness washers are used
>instead of 5/16 inch washers?

One possible solution is to consider whether pretension is actually required in the first place. If the bolts are in shear, snug-tightened installation of A490s is often acceptable (pretension is often not required). And per RCSC Specification Section 6.1.2, for snug-tightened bolts in slotted holes in exterior plies, a standard ASTM F436 washer is suitable.

Hope this helps.

Charlie

P.S. If you don;t already have it, you can get the 2000 RCSC Specification as a free download from http://www.boltcouncil.org.