Page 306 - Handbook of Structural Steel Connection Design and Details

Partially Restrained Connections

Partially Restrained Connections 291

where Y 1 if (F /F ) < 0.8 or 1.1 otherwise. In order to ensure a duc-
t y u
tile failure, the ratio of the effective area (A ) to the gross area (A ) of
e g
the plate should be at least:
A e R F y
y
$ (4.2)
A g R g F u
2. For the case of seismic loads another key issue is the design of
the welds to the column flange. In this area there are recent,
detailed guidelines proposed by SAC (FEMA, 1995, 1997a) and AISC
358 (2005). The AISC provisions require that a welding procedure
specification (WPS) be prepared as required by AWS D1.1 (AWS,
2005). AWS D1.1 provides detailed procedures for welding (see
Chap. 3) and this standard should become familiar to all structural
engineers. In addition, a minimum Charpy V-Notch test (CVN)
toughness of 20 ft-lb at –20
F is required of all filler metal by the
seismic AISC specification.
3. Local buckling criteria: The current limits suggested by AISC
(2005) 0.38 2 sE>F d for b/t in beam flanges in compression and
y
3.76/2 sE>F y d for webs in flexural compression seem to provide a rea-
sonable limit to ensure that the nominal plastic moment capacity of
the section is reached. For seismic applications, these limits have
been tightened somewhat to 0.30 2 sE>F d for b/t in beam flanges and
y
d for webs in flexural compression to
something less than 3.142 sE>F y
ensure not only that the capacity can be reached, but also that suffi-
cient rotational ductility is available. The typical buckle that forms
when these criteria are met is a smooth, small local buckle. This pre-
cludes the development of a sharp buckle that may lead to fracture
under reversed inelastic loading. The current limits on web slender-
ness also seem to provide reasonable limits although the actual per-
formance will be tied to the detailing of the web connections and
whether composite action is expected. The slenderness of the connec-
tion plates, measured between the weld to the column flange and the
centerline of the first row of bolts, should also be kept as low as prac-
ticable to prevent the formation of a local or global buckle in this
area. Current criteria for unsupported compression elements are
applicable in this case.
4. Bolts: The bolt group should be designed not only to prevent a
shear failure of the connectors but also to provide adequate perfor-
mance during the slipping phase of the moment-rotation behavior.
Since slip provides a good energy-dissipation mechanism, it is pru-
dent to design the connection such that the slip occurs well above the

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