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Re: [SEAOC] Steel Moment Connections with Cover Plates

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On3/27 - Anthony Tarek wrote:
> This question is in regard to steel moment connections with cover plates.
> Most of the test conditions and published results (i.e FEMA guidelines)
> that I have seen have a continuous column with a beam butting against it.
> If a beam is continuous over the column is it necessary to use cover plates
> on the beam? And if so, does this effectively shift the plastic hinge away
> from the connection.
> Another scenario is to place cover plates at the column flanges instead of
> beam flanges. Does this strengthen or adversely undermine the column
> connection?

Running the beam through the column may be an effective solution in 
some cases.  This would not shift the plastic hinge away from the 
joint.  You would still have a plastic hinge forming at the face of 
the column, where presumably, you would have a joint in the column 
flange, however, you would probably not be placing this welded joint 
into a plastified condition, so long as the column is of adequate 
strength relative to the beam to assure that plastic action occurs in 
the beam.

Please note however, that you introduce a discontinuity (the welded 
joint) into the column at a point of high stress, which is genearlly 
not good practice.   Essentially, you are introducing a column splice 
at the point of highest stress.  While this is not prohibited, it can 
result in fracture initiation in the column, if the weld is of 
inadequate toughness and incorporates sufficiently large  flaws or 
discontinuities.  Full penetration welds should always be specified 
for this joint, not partial penetration, as the partial penetration 
weld can easily initiate fracture under high stress demand.

You may be interested to note that a detail somewhat similar to this 
is quite common in Japan.  A number of buidlings using this detail 
in Kobe experienced fracture at the column to girder splice 
connection, as a result of either the use of fillet welds for this 
joint, partial penetration welds, or welds of inadequate toughness.

If this detail is attempted, it would be a good idea to perform some 
qualitifcation testing, as I am not aware of any available data on 
the performance of this connection type.  Also, the full pen welds of 
the column flanges to the beam should incorporate notch tough weld 
metal (20 ft-lbs at 0deg. F) as suggested by the SAC Interim 
Guidelines (FEMA-267)  for critical joints.

Ron Hamburger
Project Director for Product Development
SAC Steel Project
Ronald O. Hamburger, SE
Regional Manager
EQE International, Inc.
San Francisco, California