Page 303 - Handbook of Structural Steel Connection Design and Details

Partially Restrained Connections

288 Chapter Four

order of occurrence] and fracture mechanisms [mechanism (10), any
of which will led to connection failure]. For many PR connections
the numerous sources of deformations provide considerable ductility
but complicate the design. Designers are encouraged to develop
their own lists and rankings based on their experience and regional
preferences of fabricators and erectors.
Special note should be made of the fact that the material properties
play an important role in connection performance. In particular, the
separation between the expected yield (R F ) and expected ultimate
y y
strength (R F ) of the material is a key factor. As our understanding
t u
of the failures in steel frames during the 1994 Northridge earthquake
improves, it is clear that material performance played an important
role in some of the failures encountered. Issues related to the ductility
and toughness of the base materials for both welds and bolts, installa-
tion procedures, QA/QC in the field, and need for new, tighter materi-
al specifications have received considerable attention (FEMA, 1997a).
Designers should strive to obtain the latest information in this area
so that future failures can be avoided.
The design process outlined places a heavy additional burden on
designers both in terms of professional responsibility and continuing
education, not to mention substantial additional design time. Two
important points need to be made with respect to these issues. First,
as our designs become more optimal with respect to both strength and
stiffness, many of the traditional assumptions made in design need to
be carefully reexamined. These include, for example, serviceability
criteria based on substantially different partition and cladding sys-
tems than those used today. Second, these optimized systems are far
more sensitive to the assumptions about connection behavior since
typically far fewer moment-resisting connections are used in steel
frames today than 20 years ago.
In this section the fundamentals of design for full-strength, fully
restrained (FS/FR) bolted connections will be discussed first, followed
by that for partial-strength, partially restrained (PS/PR) ones. The
design for both seismic and nonseismic cases will be discussed. The
emphasis will be on understanding the basic steps in connection
design and developing an understanding of the crucial mechanisms
governing their behavior.

4.3.1 Column-welded–beam-bolted
connections
The design and behavior of column-welded–beam-bolted (CW-BB)
connections (Fig. 4.9) has been discussed extensively by Astaneh-Asl
(1995) and Schneider and Teeraparbwong (2002). The mechanistic
model for this type of connection, labeled column-bolted–beam-bolted

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