Page 266 - Handbook of Structural Steel Connection Design and Details

Welded Joint Design and Production

Welded Joint Design and Production 251

result of the increased cross section at the weld. This region, inca-
pable of ductility, must be kept below the critical tensile stress, and
the increase in area accomplishes this goal. Second, and most impor-
tant, the most highly stressed region is now at point B, the region of
the beam that is capable of exhibiting ductility. Assuming good work-
manship with no defects or stress raisers, the real success of this con-
nection will depend upon getting the adjacent beam to bend plastically
before this critical section cracks. The way in which a designer selects
structural details under particular load conditions greatly influences
whether the condition provides enough shear stress component so
that the critical shear value may be exceeded first, producing suffi-
cient plastic movement before the critical normal stress value is
exceeded. This will result in a ductile detail and minimize the
chances of cracking.
Details of welded connections. There are no secondary members in
welded construction. Any material connected by a weld participates in
the structural system—positively or negatively. Unexpected load
paths can be developed by the unintentional metallurgical path that
results from the one-component system created by welding. This must
be considered in all phases of a welded steel project but is particularly
significant in detailing.
Weld backing. Weld backing consists of auxiliary pieces of material
used to support liquid weld puddles. The backing can be either tempo-
rary or permanent. Permanent backing consists of a steel member of
similar composition that is fused in place by the weld. The D1.1 code
requires that backing, if used, be continuous for the length of the
joint, free of interruptions that would create stress-concentration fac-
tors. Segments of backing can be made continuous if complete joint-
penetration (CJP) groove welds join the various segments of backing.
It is essential that these splices be completely fused across the back-
ing cross section.
Weld tabs. Weld tabs are auxiliary pieces of metal on which the
welding arc may be initiated or terminated. For statically loaded
structures, these are typically left in place. For seismic construction,
it is recommended that weld tabs be removed from critical connec-
tions that are subject to inelastic loading. It is in the region of these
weld tabs that metal of questionable integrity may be deposited. After
removal, the end of the weld joint can be visually inspected for
integrity.
Weld tab removal is probably most significant on beam-to-column
connections where the beam flange width is less than the column
flange width. It is reasonable to expect that stress flow would take
place through the left-in-place weld tab. In contrast, for butt splices

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