Page 290 - Handbook of Structural Steel Connection Design and Details

Partially Restrained Connections

Partially Restrained Connections 275

Figure 4.1 Cyclic performance of T-stub connection.

diaphragm. PR connections may benefit significantly from using rein-
forcing bars in the floor slabs to carry negative moments over the sup-
ports and to redistribute forces in the connection region. The design of
this type of composite PR connection has been covered in detail in
several publications (Leon et al. 1996, Leon, 1997), and a short sum-
mary of the topic is given at the end of the chapter.

4.2 Connection Classification
From the fifth to the eighth edition of the allowable stress specifica-
tion (AISC, 1947, 1978), PR connections were categorized as Type 3
construction. The Type 3 design was predicated on the assumption
that “connections of beams and girders possess a dependable and
known moment capacity intermediate in degree between the rigidity
of Type 1 (rigid) and the flexibility of Type 2 (simple).” This definition
is confusing since it mixes strength and stiffness concepts, and was
generally interpreted as referring to the initial stiffness (K ) of the
i
connection as characterized by the slope of its moment-rotation curve
(Fig. 4.2c). Moreover, these specifications allowed the use of PR con-
nections in “wind frames” under the Type 2 (simple framing) classifi-
cation, where the connections were assumed as simple for gravity
loads and rigid for lateral loads. Until the early 1980s, many steel
frames were designed using PR connections through this artifice,
which has disappeared from the most recent specifications.

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