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RE: Dogbone Connections

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There have been a number of tests of "dogbone" connections conducted 
over the past 15 years.  This is not really a new idea.  Of the 
various post-Northridge moment connections, this one appears to 
provide a good combination of economy and reliability in testing to 
date.  The SAC Joint Venture is currently in the process of 
publishing an Interim Guidelines Advisory - as a supplement to FEMA-
267.  Among other things, this contains a detailed design procedure 
for dogbone connections.  FEMA will distribute this free of charge to 
all holders of the FEMA-267 document.  It should be available in 
about 30 days.

Engineers desiring to specify dogbones should be aware that there are 
several alternative shape configurations for the cut outs in the 
flanges.  Of these, the circular arc appears to be the most promising 
with regard to performance.  This configuration has not been tested 
as much as several other types.  However, there has been limited 
testing of this type by Mike Engelhardt at U.T. Austin and by E. 
Popov at U.C. Berkeley.

There are several critical issues to be aware of:
1- Interaction with slab effects may be critical.  The slab, if not 
properly detailed, could prevent the dogbone from providing the 
intended fuse action.  Recent testing by Ecole Polytechnic in 
Montreal suggests that it is possible to obtain good behavior by 
omittting attachments between the slab (metal deck) and the beam in 
the region of the dogbone cutouts and by leaving a gap between the 
face of the column and the slab, to permit unrestrained relative 
rotation.

2- The reduced section at the flange cut outs has a reduced warping 
resistance and is subject to lateral buckling.  It should be braced 
with transverse framing or "kickers".

3- Designers should avoid welding to the beam directly within the 
dogbone region as this can cause potential stress risers that will 
initiate fracture during cyclic inealstic deformation.

Ronald O. Hamburger
Project Director for Product Development
SAC Joint Venture