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Re: Oversizing Galvanized Bolt Holes

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Rickard,

This question comes up frequently and has been answered several times in AISC Modern Steel Construction.  The standard reply is that you should NOT oversize bolts holes due to galvanizing.  Here is one such link from MSC:

http://www.modernsteel.com/steelinterchange_details.php?id=822

Thomas Hunt, S.E.
Fluor



Richard Calvert <RichardC(--nospam--at)lbbe.com>
07/14/2009 01:22 PM
Please respond to seaint
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Subject
Oversizing Galvanized Bolt Holes





I’m being told that it is ‘required’ to use a standard OVS bolt hole for members that are to be hot dip galvanized by a detailer on a job.  Something that I was admittedly never aware of. 
In this case they are doing this for a tension splice.  My design was based on standard holes and a bearing type connection. 
So, do I need be using slip-critical connections to keep the splice from forming a gap due to the extra size of the holes?
Does the hole HAVE to be a full 15/16” for a ¾” bolt? Or is something like 7/8” acceptable?
How does the hole surface maintain any real thickness of zinc coating with several thousand PSI bearing on it anyways? In other words, why go through the trouble of oversizing for fear of ruining the coating if once the bolt is engaged it will seemingly ruin it anyways?
 
Doing my own research I’ve found three different answers… one says that no increase is required… another says it does, and another says that the holes must be tapped after the galv. process…
 
 
Richard Calvert, EIT
Project Engineer
 
Lindemann Bentzon Bojack
Architects & Engineers
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