If you want the bolt to fit - I would say yes!! Say you have 1/2'' holes and 1/2'' bots... It is often a bit@@ to get those in because the bolts have some burrs or even the holes are burred....
I think sail was asking if the bolts holes should be 1/16" larger than the standard (d+1/16") opening (i.e. d +1/8" total) to accommodate the thickness of the galvanizing.
I must admit that I've never thought about that before and I haven't done it, although it does seem like a valid question.
Hot-dip galvanizing is a zinc coating applied to bare steel, and typical coatings range from 3-8 mils (75-200 microns). Therefore, when steel is dipped in molten zinc, the steel becomes slightly thicker. When designing and detailing tapped holes, even the smallest change in thickness is important. When the decision is made to hot-dip galvanize, hole sizes in certain products must be oversized to account for the added thickness of the zinc coating to the edges.
As it can be difficult to predict the exact thickness of the zinc coating, if the hole is not large enough after galvanizing, it can be retapped. Even though retapping will leave exposed bare steel, regalvanizing is not required as the zinc coating on the mating fastener will protect chased or retapped nuts cathodically.
For holes threaded after galvanizing, the hole should be drilled undersize before galvanizing so the threads can be cut after galvanizing.
* ASTM Overtapping Guidelines
Clearance holes must be designed to account for zinc pickup. Oversizing holes according to ASTM guidelines is usually sufficient to account for the thickness of the zinc coating, or the holes can be reamed to fit after galvanizing.
Threaded assemblies must adequately accommodate galvanized fasteners. It is important to make sure the hole is undersized enough so when cutting the threads, all zinc is removed and the hole is still accurately sized. If all of the zinc is not removed from the threaded hole, its relatively soft structure may become damaged when fitting the hole with a fastener. It is best to mate a galvanized fastener with threads solely composed of steel to ensure a quality bolted connection. Cut threads will expose bare steel, but the zinc coating on the threads of the mating hot-dip galvanized fastener will protect the bare steel for the bolted connection.
Utilizing galvanized fasteners is always recommended when connecting galvanized structural pieces, and uncoated fasteners should never be placed in galvanized threaded holes. Zinc’s cathodic protection characteristics cause it to sacrifice itself to protect the uncoated fastener, accelerating the rate in which zinc is consumed.
The use of very small holes should be minimized as well, as they may become completely obscured and/or filled by zinc. If small holes are unavoidable, the area may be heated after galvanizing in order to remove any excess zinc and open the hole.
Only issues I have ever run into were properly over-tapped nuts on large galvanized anchor rods. I had some 2 1/2" chinese galvanized nuts that weren't even close to fitting on hot-dipped galvanized anchor rods. At first I thought the threaded rods weren't properly cleaned but it turned out the chinese nuts were way off. I got some U.S. nuts and they fit perfectly.
If you want to use a bearing condition, you can't make the hole larger than normal. If you do make it larger than a standard hole, you would have to use a slip critical condition.
2.4.4. Are there any special hole size requirements in members or bolts that are galvanized?
No. Holes for galvanized bolts or members are not permitted to be larger than those specified in Table 3.1 of the 2004 RCSC Specification for Structural Joints Using ASTM A325 or A490 Bolts.
I have done several galvanized structures and can honestly say, that with good steel fabs and a good HD galvanizer, it should not be a problem.
I have done several flange type splices in tapered poles and dead end structures that had HD galv and 1/16" over-sized holes with up to 16 bolts in one pattern and they went up without a hitch. I think it just comes down to quality and craftsmanship.
Toad and nutte are correct. There is no need to oversize the holes, and if you do, you have to design the connections as slip critical, which requires special preparation of the galvanized faying surfaces. Another reference...
looks like the answer is no allowance in bolt hole size for galvanizing..even though it goes against my intuition..
I really appreciate all the replies and input....thanks
Sail
I think you have the correct answer. There in no RCSC criteria for a "little bigger" standard hole for a bearing connection. Thus anything larger than the specified standard hole must be designed and installed as slip critical. In most cases these connections fit with little trouble if detailed and fabricated correctly.
Note: if you are using larger bolts > 1 1/4 diameter, problems can occur with standard holes. The ASTM tolerance for overrun on these bolt diameters can theoretically exceed the diameter on a standard hole with the small loss caused by the coating.
