Page 295 - Handbook of Structural Steel Connection Design and Details

Partially Restrained Connections

280 Chapter Four

M connection
M p,beam Relative

Brittle Ductile
1.2
SMF ND
1.0

0.8
IMF ID = 2%
0.6 SMF D
Brittle Ductile
IMF D >0.8M p,beam
0.4 at ID = 4%
SMF ID = 4%
0.2 Brittle Ductile
3
Rotation (rad × 10 )
2 10 20 30 40
Ductility (µ)
1 2 3 4 5 6 7 8
Figure 4.4 Possible connection ductility classification.

shown in Fig. 4.3, this definition is troublesome since a yield moment
is difficult to determine. In this case, for the case of the connection in
a special moment frame with no degradation (SMF, solid line) and for
illustrative purposes only, the yield rotation is defined as the rotation
at the intersection of the service and hardening stiffnesses of the con-
nection. In general, relative ductilities of 3 or more are associated with
well-detailed, nonseismic connections and general relative ductilities
of 6 or more are associated with well-detailed, seismic connections.
Since the end of the work on the SAC (a join venture of research orga-
nizations in California) projects, the qualifications for connection perfor-
mance has undergone two significant changes. First, the performance
criteria for special and intermediate moment frames (0.04 rad of total
connection rotation for SMF and 0.03 rad for IMF, both including an
assumed 0.01 rad of elastic deformation) has been changed to the total
interstory drifts (ID 4 and 2%, for SMF and IMF respectively). These
are also shown in Fig. 4.4, but their location in this figure is arbitrary
with respect to the axes. In addition, the original requirement that
the connection capacity at 0.04 rad should not decrease by more than
20% from its maximum has been changed to a requirement that at
4% drift SMF connections should not have less than 80% of the nomi-
nal flexural capacity of the beam. These two are significant changes,
as direct conversions between both interstory drift and connection
rotation, and connection and beam strength are not possible.

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