Page 55 - Handbook of Structural Steel Connection Design and Details

Design of Connections for Axial, Moment, and Shear Forces

40 Chapter Two

bolts or welds, let the economics of fabrication and erection play a role
in the choice. Different fabricators and erectors in different parts of the
country have their preferred ways of working, and as long as the prin-
ciples of connection design are followed to achieve a safe connection, local
preferences should be accepted. Some additional considerations that
will result in more economical connections (Thornton, 1995B) are:
1. For shear connections, provide the actual loads and allow the use of
single plate and single angle shear connections. Do not specify full-
depth connections or rely on the AISC uniform load tables.
2. For moment connections, provide the actual moments and the actual
shears. Also, provide a “breakdown” of the total moment, that is, give
the gravity moment and lateral moment due to wind or seismic loads
separately. This is needed to do a proper check for column web dou-
bler plates. If stiffeners are required, allow the use of fillet welds in
place of complete joint penetration welds. To avoid the use of stiff-
eners, consider redesigning with a heavier column to eliminate them.
3. For bracing connections, in addition to providing the brace force, also
provide the beam shear and axial transfer force. The transfer force
is the axial force that must be transferred to the opposite side of the
column. The transfer force is not necessarily the beam axial force that
is obtained from a computer analysis of the structure. See Thornton
(1995B) and Thornton and Muir (2008) for a discussion of this. A
misunderstanding of transfer forces can lead to both uneconomic and
unsafe connections.

2.1.4 Types of connections
There are three basic forces to which connections are subjected. These are
axial force, shear force, and moment. Many connections are subject to two
or more of these simultaneously. Connections are usually classified accord-
ing to the major load type to be carried, such as shear connections, which
carry primarily shear; moment connections, which carry primarily
moment; and axial force connections, such as splices, bracing and truss con-
nections, and hangers, which carry primarily axial force. Subsequent sec-
tions of this chapter will deal with these three basic types of connections.

2.1.5 Organization
This chapter will cover axial force connections first, then moment con-
nections, and lastly shear connections. This is done to emphasize the
ideas of load paths, limit states, and the lower bound theorem, which
(except for limit states) are less obviously necessary to consider for the
simpler connections.

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