Tuesday, July 14, 2009

Re: Oversizing Galvanized Bolt Holes


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:


Thomas Hunt, S.E.

Richard Calvert <RichardC@lbbe.com>
07/14/2009 01:22 PM
Please respond to seaint
"seaint@seaint.org" <seaint@seaint.org>
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
290 Citrus Tower Blvd, Suite 200, Clermont, Fl. 34711
tel: 352.242.0100 ext.141 fax: 352.242.0302
Proudly Serving America's Top Builders
Internet Email Confidentiality
Privileged/Confidential Information may be contained in this message.

If you are not the addressee indicated in this message (or responsible
for delivery of the message to such person), you may not copy or deliver
this message to anyone. In such case, you should destroy this message
and kindly notify the sender by reply email. Please advise immediately if
you or your employer do not consent to Internet email for messages of
this kind. Opinions, conclusions and other information in this message
that do not relate to the official business of my firm shall be understood
as neither given nor endorsed by it.
------------------------------------------------------------ The information transmitted is intended only for the person  or entity to which it is addressed and may contain  proprietary, business-confidential and/or privileged material.   If you are not the intended recipient of this message you are  hereby notified that any use, review, retransmission, dissemination,  distribution, reproduction or any action taken in reliance upon  this message is prohibited. If you received this in error, please  contact the sender and delete the material from any computer.    Any views expressed in this message are those of the individual  sender and may not necessarily reflect the views of the company.   ------------------------------------------------------------