Page 242 - Handbook of Structural Steel Connection Design and Details

Welded Joint Design and Production

Welded Joint Design and Production 227

material, where the minimum specified filler metal/base metal prop-
erties for yield are 60/50 ksi and for tensile are 70/65 ksi. Even
though the filler metal has slightly higher properties than the base
metal, this is considered to be a matching combination.
Many see the filler metal recommendations provided in codes that
reference “matching” combinations for various grades of steel and
assume that is the only option available. While this will never gener-
ate a nonconservative answer, it may eliminate better options.
Matching filler metal tables are designed to give recommendations for
the one unique situation where matching is required (for example,
CJPs in tension). Other alternatives should be considered, particularly
when the residual stresses on the welded connection can be reduced
in crack-sensitive or distortion-prone configurations.
Matching filler metal is required for CJP groove welds loaded in
tension. In order to achieve a full-strength welded connection, the
filler metal must have a strength that is at least equal to that of the
material it joins.
Undermatching weld metal may be used for all weld types and load-
ing types except one: complete joint penetration groove welds loaded
in tension. For all other joints and other loading types, some degree of
undermatching is permitted. For example, CJPs in compression may
be made with weld metal that has a strength of up to 10 ksi less than
matching. CJPs in shear or loading parallel to the longitudinal axis
may be made with undermatching filler material. All PJPs, fillet
welds, and plug or slot welds may be made with undermatching weld
metal. Design of the weld sizes, however, must incorporate the lower
filler metal strength in order to ensure the welded connection has the
proper capacity.
Undermatching may be used to reduce the concentration of stresses
in the base material. Lower-strength filler material generally will be
more ductile than higher strength weld metal. In Fig. 3.21, the first
weld was made with matching filler material. The second design uti-
lizes undermatching weld metal. To obtain the same capacity in the

Figure 3.21 Matching and undermatching filler
metal. (Courtesy of The Lincoln Electric Company.)

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