Page 273 - Handbook of Structural Steel Connection Design and Details

Welded Joint Design and Production

258 Chapter Three

ASTM steel specifications need additional controls that will limit
the upper value of acceptable yield strengths for materials as well as
the ratio of F /F . A new ASTM specification has been proposed that
y u
will address these issues, although its approval will probably not be
achieved before 1997.
In Fig. 3.36, five zones have been identified in the area of the con-
nection, with the sixth material property being located in the beam.
Thus far, only two have been discussed, namely, the beam yield
strength and the beam ultimate strength. As shown in the figure,
these are designated with the subscript X to indicate that these are
the properties in the orientation of the longitudinal axis of the beam.
The properties of interest with respect to the column are oriented
in the column Z axis. This is the direction which will exhibit the least
desirable mechanical properties. Current ASTM specifications do not
require measurement of properties in this orientation. While there
are ASTM standards for the measurement of through-thickness prop-
erties (ASTM 770), these are not normally applied for structural
applications. It is this through-thickness strength, however, that is
important to the performance of the connection.
The weld metal properties are also very important, as indicated by
the designation F in Fig. 3.36. These are discussed in “Weld Metal
u w
Properties.”
On either side of the weld are two heat-affected zones (HAZ), one
located on the column side of the weld and the other located on the
beam side. These properties are also important to the performance of
the connection and are discussed in “Heat-Affected Zones.”
Notch toughness is defined as the ability of a material to resist
propagation of a preexisting cracklike flaw while under tensile stress.
Pre-Northridge specifications did not have required notch toughness
for either base materials or weld metals. When high loads are
applied, and when notchlike details or imperfections exist, notch
toughness is the material property that resists brittle propagation
from that discontinuity. Rolled shapes routinely produced today,
specifically for lighter-weight shapes in the group 1, 2, and 3 category,
generally are able to deliver a minimum notch toughness of 15 ft lb at
40°F. This is probably adequate toughness, although additional
research should be performed in this area.
For heavy columns made of group 4 and 5 shapes, this level of
notch loughness may not be routinely achieved in standard produc-
tion. After Northridge, many engineers began to specify the supple-
mental requirements for notch toughness that are invoked by AISC
specifications for welded tension splices in jumbo sections (group 4
and 5 rolled shapes). This requirement for 20 ft lb at 70°F is obtained
from a Charpy specimen extracted from the web-flange interface, an

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