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Steel Designers' Manual - 6th Edition (2003)
8 max _________
_______ 4 I
I II I
(a) (b)
introduce a bending stress that would open the root. Bending to close the root is
admissible, and fillet welds on both sides of a member will prevent root opening.
24.3.3 Butt welds
Recommendations for cost reduction 695
Fig. 24.4 Fillet weld configurations for (a) T-joints, (b) lap joints, (c) corner joints
Whereas fillet welds join the surfaces of adjacent members, butt welds join all or
part of their cross section, and are consequently called full or partial penetration
welds. Even where the joint configuration requires the use of a butt weld, partial
penetration is often sufficient, instead of full penetration. Designers should state the
weld throat dimension required, instead of routinely demanding full penetration
with its extra difficulties and costs. Current practice is to use suitable weld preparations,
procedures, and approved welders to ensure the required depth of fusion
for the throat size. When partial penetration is adequate the designer should not
state, ‘All butt welds must have full penetration’. To a welding engineer, this means
full penetration through the sections, when all that is intended is for the steelwork
contractor to show proof of achieving the required throat depth. Figure 24.5 shows
different approaches to butt welds. The partial penetration weld (Fig. 24.5(a)) is the
most economical to prepare and weld. Throat size can be ensured by use of highcurrent
MIG/MAG, flux-cored arc, or submerged arc welding, and the fabricator can
be asked to provide proof of consistent penetration. Where full penetration is
justified, welds should be made with backing (as Fig. 24.5(b)). Where backing is not
permissible, welds are made by welding one side, grinding or gouging the root to
sound metal for completion from the other side (Fig. 24.5(c)).
r'H\jHV
(a) (b) (c)
Fig. 24.5 Partial penetration butt welds
(c)