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CONNECTIONS

CONNECTIONS 3.39

3.3 GENERAL CONNECTION DESIGN PROCEDURE

Determine the external (applied) factored loads, also called required strengths, and their lines of
action. Make a preliminary layout, preferably to scale. The connection should be as compact as pos-
sible to conserve material and to minimize interference with utilities, equipment, and access. Decide
on where bolts and welds will be used and select bolt type and size. Decide on a load path through
the connection. For a statically determinate connection, there is only one, but for indeterminate con-
nections there are many possibilities. Use judgment, experience, and published information to arrive
at the best load path. Now provide sufficient strength, stiffness, and ductility, using the limit states
identified for each part of the load path, to give the connection sufficient design strength, that is, to
make the connection adequate to carry the given loads. Complete the preliminary layout, check
specification-required spacings, and finally check to ensure that the connection can be fabricated and
erected. The examples of this chapter will demonstrate this procedure.

3.3.1 Economic Considerations
For any given connection situation, it is usually possible to arrive at more than one satisfactory solu-
tion. Where there is a possibility of using bolts or welds, let the economics of fabrication and erec-
tion play a role in the choice. Fabricators and erectors in different parts of the country have their
preferred ways of working, and as long as the principles of connection design are followed to achieve
a safe connection, local preferences should be accepted. Some additional considerations which will
result in more economical connections (Thornton, 1995b) are as follows.

1. For shear connections, design for the specified factored 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, design for the specified factored moments and 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 doubler
plates. If stiffeners are required, allow the use of fillet welds in place of complete joint-penetration
welds. To avoid the use of stiffeners, 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. As discussed in Art. 3.1.6, 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. A misunderstanding of transfer
forces can lead to both uneconomic and unsafe connections.

3.3.2 Types of Connections

There are three basic forces to which connections are subjected: axial force, shear force, and moment.
Many connections are subject to two or more of these simultaneously. Connections are usually classified
according 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 connections, hangers, etc., which carry primarily axial force.

3.3.3 Strength Limit States
Many of the limit states that govern main-member design also must be considered in the design of
connection elements.

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