Page 285 - Handbook of Structural Steel Connection Design and Details

Welded Joint Design and Production

270 Chapter Three

approach may be technically possible, although the degree of control
necessary on both the material properties and the welding operations
may not be practical.
Cover-plated designs. This concept uses short cover plates that are
added to the top and bottom flanges of the beam. Fillet welds transfer
the cover-plate forces to the beam flanges. The bottom flange cover
plate is shop-welded to the column flange, and the bottom beam
flange is field-welded to the column flange and to the cover plate.
Both the top flange and the top flange cover plate are field-welded to
the column flange with a common weld. The web connection may be
welded or high-strength bolted. Limited testing of these connections
has been done, with generally favorable results.
The cover-plate approach has received significant attention after
Northridge because it offered early promise of a viable solution. Other
methods may emerge as superior as time progresses. While the cover-
plate solution treats the beam the same as other approaches (that is,
it moves the plastic hinge into a region where ductility can be demon-
strated), it concentrates all the loading to the column into a relatively
short distance. Other alternatives may treat the column in a gentler
manner.

Flange rib connections. This concept utilizes one or two vertical ribs
attached between the beam flanges and column face. In a flange rib
connection, the intent of the rib plates is to reduce the demand on the
weld at the column flange and to shift the plastic hinge from the column
face. In limited testing, flange rib connections have demonstrated
acceptable levels of plastic rotation provided that the girder flange
welding is correctly done.
Vertical ribs appear to function very similarly to the cover-plated
designs but offer the additional advantage of spreading that load over
a greater portion of that column. The single rib designs appear to be
superior to the twin rib approaches because the stiffening device is in
alignment with the column web (for I-shaped columns) and facilitates
easy access to either side of the device for welding. It is doubtful that
the single rib would be appropriate for box column applications.
Top and bottom haunch connections. In this configuration, haunches
are placed on both the top and bottom flanges. In two tests of the top
and bottom haunch connection, it has exhibited extremely ductile
behavior, achieving plastic rotations as great as 0.07 rad. Tests of sin-
gle, haunched beam-column connections have not been as conclusive;
further tests of such configurations are planned.
Haunches appear to be the most straightforward approach to
obtaining the desired behavior out of the connection, albeit at a fairly
significant cost. The treatment to the column is particularly desirable,

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