Just to give you an idea of what other fabricators are doing - I just
finished reviewing shop drawings that involve tens of thousands of
galvanized high strength bolts where the holes are fabricated 1/16" larger
than the bolt.
> -----Original Message-----
> From: Bohm, Gabriel [SMTP:GBohm(--nospam--at)kticorp.com]
> Sent: Tuesday, April 13, 1999 2:57 PM
> To: 'seaint(--nospam--at)seaint.org'
> Subject: Holes for galvanized bolts
> A certain steel fabricator insists that hole diameters for galvanized
> bolts must be the nominal bolt size plus 1/8 inch. They say it's because
> of the increased bolt diameter due to galvanizing. We would like them to
> provide standard holes, as the diameter increase is deemed to be
> negligible, when galvanizing follows the requirements of ASTM A325
> paragraph 4.3.4.
> We're talking about bearing type connections using ¾, 7/8 and 1 inch
> diameter A325 bolts.
> Neither AISC's Specification for Structural Steel Buildings, nor RCSC's
> Specification for Structural Joints using ASTM A325 or A490 Bolts appear
> to have the definitive answer to our dispute. Both codes recognize
> standard and oversize holes (bolt diameter, plus 1/16 and 3/16 inch,
> respectively). No word about a 1/8 inch increase.
> Paragraph J3.2.c of the AISC specification states that oversized holes
> "shall not be used in bearing-type connections". This leaves us with the
> standard hole option only. But here's what the RCSC specification says
> in its Commentary C3 Bolted Parts: "Research has shown that, where
> greater latitude is needed in meeting dimensional tolerances during
> erection, somewhat larger holes can be permitted for bolts 5/8 inch
> diameter and larger without adversely affecting the performance of shear
> connections assembled with high-strength bolts. The oversize and slotted
> hole provisions of this Specification are based upon these findings".
> Well, if bolts in oversize holes perform OK, why does AISC prohibit
> their use? In other words, can I accept the fabricator's approach
> without violating codes? I'm sure some of you have encountered this
> problem before. Any suggestion will be appreciated.
> Gabe Bohm
> San Dimas, Ca.