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RE: Holes for galvanized bolts

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This issue came up a few years back and I did an informal telephone survey 
of fabricatorsto find some answers. The fabricators I talked to 
acknowledged that galvanizing can create a problem with getting bolts 
through the holes if standard holes are used (1/16-in. clearance). However, 
they also indicated these problems were more the exception than the rule 
and usually resulted when there was an unusual build-up of galvanizing 
inside the hole. A few fabricators indicated that their galvanizers use 
compressed air to "blow out" the holes after galvanizing, which eliminates 
this. Others said they didn't do this, but still rarely had any problems.

I also looked into specification requirements (AISC and RCSC). There are no 
specific provisions that address hole sizes for galvanizing as being any 
different than those for other applications. The specs simply state the 
maximum hole sizes that can be used for standard, oversized, short-slotted 
and long-slotted holes. A 1/32-in. tolerance is implicit in these nominal 
values allows a slightly larger hole that might result from the punching or 
drilling equipment or a very slight amount of reaming. But I don't see 
anything that permits standard holes to be made with a 1/8-in. clearance 
when galvanized.


-----Original Message-----
From:	Bohm, Gabriel [SMTP:GBohm(--nospam--at)]
Sent:	Tuesday, April 13, 1999 4:57 PM
To:	'seaint(--nospam--at)'
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 ?, 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.