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RE: Moment Frames with Slip Critical Shear Connection

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Charlie is right regarding what the AISC Spec "requires" but I will offer a
differing opinion. I feel that bolts should be slip-critical when used with
welds even if "not on the same faying surface". If bolts are not
slip-critical, then it may require some movement for them to develop
strength in bearing. But the welds will be very rigid and will prevent
movement. Thus the welds may effectively carry all of the load until the
welded connection deforms adequately for the bolts to go into bearing. 
 
The assumption that bolts will be in bearing due to self-weight is just that
- an "assumption". It is not "required" by the Spec and may not be a valid
assumption in the case of uplift or axial load on the connection. 


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

________________________________

	From: Carter, Charlie [mailto:carter(--nospam--at)aisc.org] 
	Sent: Monday, July 26, 2004 7:28 AM
	To: seaint(--nospam--at)seaint.org
	Subject: RE: Moment Frames with Slip Critical Shear Connection
	
	> ... SDC C ... designed as "steel structures not specifically
	>detailed for seismic resistance" (R=3).  The moment connection
	>consists of flange plates welded to the column and beam.  The
	>shear connection calls for the bolts in the shear connection to
	>be slip-critical.  I thought this was a requirement for moment
	>connections?  Do the bolts in the shear connection have to be
	>slip-critical?

When bolts and welds share load on the same faying surface, the AISC Spec
has a requirement that the bolts be slip critical. In this case, the bolts
and welds do not share the same load, so that requirement does not apply.

I have seen these connections specified both ways and ultimately it is a
decision to be made by the engineer of record. I personally do not think a
slip of any magnitude is likely in the shear connection, since that tends to
be brought into bearing by member self weight during erection. As a result,
I would be comfortable using bearing bolts instead of slip-critical bolts.

	Charlie
	 

	 

	 

	 

	 

	 


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