Page 56 - 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 41

This chapter is based on the limit states of the AISC LRFD
Specification (AISC, 2005). The determination of loads, that is, required
strengths, is dependent upon the specific building code required for the
project, based on location, local laws, and so forth. At this time (2008),
there is much transition taking place in the determination of seismic
loads and connection requirements. Wherever examples involving seis-
mic loads are presented in this chapter, the solutions presented are
indicative of the author’s experience in current practice with many
structural engineers, and may need to be supplemented with additional
requirements from local seismic codes. Chapter 5 deals with connections
in high seismic regions and covers these additional requirements.

2.2 Axial Force Connections
2.2.1 Bracing connections
2.2.1.1 Introduction. The lateral force-resisting system in buildings
may consist of a vertical truss. This is referred to as a braced frame and
the connections of the diagonal braces to the beams and columns are the
bracing connections. Figure 2.1 shows various bracing arrangements.
For the bracing system to be a true truss, the bracing connections should
be concentric, that is, the gravity axes of all members at any joint should
intersect at a single point. If the gravity axes are not concentric, the
resulting couples must be considered in the design of the members. The
examples of this section will be of concentric type, but the nonconcen-
tric type can also be handled as will be shown.
2.2.1.2 Example 1. Consider the bracing connection of Fig. 2.2. The
brace load is 855 kips, the beam shear is 10 kips, and the beam axial
force is 411 kips. The horizontal component of the brace force is 627 kips,
which means that 627 411 216 kips is transferred to the opposite
side of the column from the brace side. There must be a connection on
this side to “pick up” this load, that is, provide a load path.
The design of this connection involves the design of four separate con-
nections. These are (1) the brace-to-gusset connection, (2) the gusset-to-
column connection, (3) the gusset-to-beam connection, and (4) the
beam-to-column connection. A fifth connection is the connection on the
other side of the column, which will not be considered here.
1. Brace-to-gusset: This part of the connection is designed first because
it provides a minimum size for the gusset plate which is then used
to design the gusset-to-column and gusset-to-beam connections.
Providing an adequate load path involves the following limit states:
1
a. Bolts (A325SC-B-N 1 / -in-diameter standard holes, serviceabil-
8
ity limit state): The above notation indicates that the bolts are

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