Page 100 - Handbook of Structural Steel Connection Design and Details

Design of Connections for Axial, Moment, and Shear Forces

Design of Connections for Axial, Moment, and Shear Forces 85

is, the load paths involved. The final connection as shown in Fig. 2.15
has small welds of the gusset to the beam and the end plate, but the rest
of the connection is very expensive. The column stiffeners are expensive,
and also compromise any connections to the opposite side of the column
3
web. The / 4-in end plate must be flame cut because it is generally too
thick for most shops to shear. The web-doubler plate is an expensive
detail and involves welding in the beam k-line area, which may be prone
to cracking (AISC, 1997). Finally, although the connection is satisfactory,
its internal admissible force distribution that satisfies equilibrium
requires generally unacceptable couples in the members framed by the
connection.
As a comparison, consider the design that is achieved by the UFM.
The statically admissible force distribution for this connection is given
in Fig. 2.14c. Note that all elements (gusset, beam, and column) are
in equilibrium with no couples. Note also how easily these internal
forces are computed. The final design for this method, which can be ver-
ified by the reader, is shown in Fig. 2.16. There is no question that this
connection is less expensive than its L weld counterpart in Fig. 2.15,
and it does not compromise the strength of the column and strut. To
summarize, the L weld method seems a good idea at the outset, but a
complete “trip” through the load paths ultimately exposes it as a fraud,
that is, it produces expensive and unacceptable connections. As a final
comment, a load path assumed for part of a connection affects every
other part of the connection, including the members that frame to the
connection.

2.2.1.7 Bracing connections utilizing shear plates. All of the bracing con-
nection examples presented here have involved connections to the
column using end plates or double clips, or are direct welded. The UFM
is not limited to these attachment methods. Figures 2.17 and 2.18 show
connections to a column flange and web, respectively, using shear plates.
These connections are much easier to erect than the double-angle or
shear plate type because the beams can be brought into place laterally
and easily pinned. For the column web connection of Fig. 2.18, there are
no common bolts that enhance erection safety. The connections shown
were used on an actual job and were designed for the tensile strength
of the brace to resist seismic loads in a ductile manner.

2.2.1.8 Connections with non-concentric work points. The UFM can be
easily generalized to this case as shown in Fig. 2.19a, where x and y
locate the specified non-concentric work point (WP) from the intersec-
tion of the beam and column flanges. All of the forces on the connection
interfaces are the same as for the concentric UFM, except that there is
an extra moment on the gusset plate M Pe, which can be applied to

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