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RE: Moment Frames with Slip Critical Shear Connection

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Charlie Carter wrote:  "I'd like you to show me how to erect a beam so that
bolts are not in bearing due to dead weight." 

My Response (Bill): I think you answered this question in your own answer
regarding "banging bolts" in the 07/01/1999 Steel Interchange: "Leaving the
drift pin in as bolts are installed and tightened tends to center the holes
in the connected plies and increases the potential for slip in the
connection." 

Charlie: "Load reversals are covered under a separate requirement in the
specification, so need not be used to confuse the questions here." 

Bill: If a roof is subject to wind uplift, the vertical reaction at the beam
connections may reverse from downward to upward. If bearing bolts are in
bearing for a downward load, won't they need to slip for an upward load? Why
isn't that an issue here? 

Charlie: "I was asking why you disagree with the rational thought that went
into the AISC recommendations you questioned."

Bill: Clearly the snug-tight condition for bearing bolts is not intended to
prevent slip - otherwise a slip-critical bolt must be used, by definition.
In my opinion, assuming that bearing bolts are always in contact in any
connection where the bolts are on a different faying surface than the welds
is not "rational". I have offered my opinions as rational thought until
offered clear evidence that reality is different. 

Charlie: "But all that has been offered to date is theory and opinion, which
is counter to the long-standing performance record of what is being
questioned." 

Bill: So far, no clear evidence that bearing bolts may always be assumed to
be in bearing has been offered - just "theory and opinion". The "banging
bolts syndrome" seems to raise questions regarding the "long-standing
performance record" of such connections. Per R. Schwein's article on "The
Banging Bolt Syndrome": "The moment resisting connections with welded
flanges and bolted webs would be less prone to this bolt slip because the
flange welds, being stiffer, would attract and resist most of the strain
before the load would cause bolt slips in the web." Please explain how a
welded flange can deform sufficiently for bolts to slip into bearing at a
web connection, such that the weld will not carry "an indeterminately larger
share of the load". To date, I do not think that AISC has presented a clear
case for its apparent position on this issue. 


William C. Sherman, PE 
(Bill Sherman) 
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com
 

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