Bolt holes oversized 1/16" or 1/8" for galvanized members 1

[IFRs]

When hot dip galvanizing is to be used, does the AISC allow 1/8" oversized holes or is it necessary to stick with 1/16" oversize? These particular connections are bearing designed but I am also interested in other connection designs are the same (friction, slip critical, etc).

 

[transmissiontowers]

We use bearing connections and galvanized steel angles with holes 1/16 larger than the bolt for 5/8 and 3/4 bolts.

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I have been called "A storehouse of worthless information" many times.

 

[WillisV]

See:

http://www.aisc.org/template.cfm?template=/ContentManagement/ContentDisplay.cfm&ContentID=27795

They recommend tapping the holes after galvanizing.

 

[transmissiontowers]

I was thinking that the holes were not threaded since IFRs specified either 1/16 or 1/8 oversize and this would be too large to get threads in. I was assuming that the holes were for bolts with nuts to connect 2 members either in a bearing type connection or a friction connection.

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[WillisV]

Good point transmissiontowers - the answer I provided really only applies to galvanized nuts or threated holes.
For just a typical bearing bolt conditition the answer is that the 1/16" clearance per AISC is adequate even for galvanized parts - see:

http://www.aisc.org/MSCTemplate.cfm...tomSource/Faq/SteelInterchange.cfm&FaqID=1943

 

[IFRs]

Yes - I meant clearance holes for bearing type connections. Thanks for the link WillisV.

Another question has come up - are slotted holes allowed for cross bracing of pipe rack type structures, as requested by our erector to make the job of erecting the steel go easier?

 

[jike]

Oversized and short slotted holes may be used without regard to direction of load. Long slots can only be used when load is applied perpendicular. Ref. pg 5-271, 9th Edition AISC manual.

It has been my practice to use oversized holes for bracing with A325 SC bolts to allow the erector some adjustment in fitup.

 

[IFRs]

Jike - is this for slip critical designs only or can bearing type connections use short slot connections?

 

[WillisV]

It is common practice for one of the connecting pieces to have short slots for easier fitup (even in bearing type simple shear connections).

 

[IFRs]

WillisV -
I appreciate that fact but I'm not able to convince the powers that be to allow it since the AISC manual does not cover it. The section quoted on page 5-271 seems to be for slip-critical not bearing connections. In addition, queries on the AISC web site bring up specific Q&A that deem slots unacceptable.

 

[WillisV]

The AISC manual does cover it quite explicitly - see following in 13th edition manual:

Double Angle Connections: p10-9 to 10-10 - read paragraph on "shop and field practices" - "Alternately, short-slotted holes can also be used."

Single Angle Connections: p10-123 - "shop and field practices" - ..."play in the open holes or horizontal slots in the angle leg may be used to provide the necessary adjustment to compenssate for mill variation."

etc. etc. etc.

As long as the slot is not IN THE DIRECTION of the applied load then it is perfectly acceptable in a standard shear connection.

Also see Item no. 32 in the "57 tips for reducing connection costs" :

http://www.aisc.org/Template.cfm?Se...Management/ContentDisplay.cfm&ContentID=22326

 

[IFRs]

Is it possible to achieve slip-critical connections on hot-dip galvanized members? Is this covered in AISC?

 

[WillisV]

Yes and Yes.

 

[IFRs]

I'll read my 9th and 10th editions again...