Page 33 - Handbook of Structural Steel Connection Design and Details

Fasteners and Welds for Structural Connections

18 Chapter One

9
Economy of fillet welds
8
7
# of Passes
6
Relative strength
5
4
3
2
1
0
3/16 1/4 5/16 3/8 7/16 1/2 9/16 5/8 11/16 3/4
Leg size (in)
Figure 1.10 Relationship of number of passes to strength.

number of passes required for some frequently used types of welds.
This table is only approximate. The actual number of passes can vary
depending on the welding process used. Figure 1.10 shows the number
of passes and fillet weld strength. It can be seen that cost, which is
proportional to the number of passes increases much faster than
strength.
Double-V and double-bevel groove welds contain about half as much
weld metal as single-V and single-bevel groove welds, respectively
(deducting effects of root spacing). Cost of edge preparation and added
labor of gouging for the back pass, however, should be considered. Also,
for thin material, for which a single weld pass may be sufficient, it is
uneconomical to use smaller electrodes to weld from two sides.
Furthermore, poor accessibility or less favorable welding position (Sec.
1.3.4) may make an unsymmetrical groove weld more economical,
because it can be welded from only one side.
When bevel or V grooves can be flame-cut, they cost less than J and
U grooves, which require planning or arc-air gouging.
For a given size of fillet weld, the cooling rate is faster and the restraint
is greater with thick plates than with thin plates. To prevent cracking due
to resulting internal stresses, the AISC Specification section J2.2 sets
minimum sizes for fillet welds depending on plate thickness, see Table 1.9.
To prevent overstressing of base material at a fillet weld the maximum
weld size is limited by the strength of the adjacent base metal.
A limitation is also placed on the maximum size of fillet welds along
edges. One reason is that edges of rolled shapes are rounded, and weld
thickness consequently is less than the nominal thickness of the part.

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