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
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.
San Dimas, Ca.