Page 93 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

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CONNECTIONS

CONNECTIONS 3.25

3.2.14 Economy in Weld Type Selection
In selecting a weld, designers should consider not only the type of joint but also the type of weld that
will require a minimum amount of metal. This will yield a saving in both material and time.
While the strength of a fillet weld varies with size, the volume of metal varies with the square of
1
the size. For example, a / 2-in fillet weld contains four times as much metal per inch of length as a
1 / 4-in weld but is only twice as strong. In general, a smaller but longer fillet weld costs less than a
larger but shorter weld of the same capacity.
Furthermore, small welds can be deposited in a single pass. Large welds require multiple
passes. They take longer, absorb more weld metal, and cost more. As a guide in selecting welds,
Table 3.7 lists the number of passes required for some frequently used types of welds. The values
in this table are only approximate. The actual number of passes can vary depending on the welding
process used.
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 (Art. 3.2.17) 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.

3.2.15 Weld Size and Length Limitations
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
(Sec. J2.2) sets minimum sizes for fillet welds depending on plate thickness, Table 3.8.
To prevent overstressing of base material at a fillet weld, the maximum weld size is limited by
the strength of the adjacent base metal.

TABLE 3.7 Number of Passes for Welds
Single-bevel groove Single-bevel groove
welds (back-up weld welds (back-up weld
not included) not included)
Weld size,* in Fillet welds 30° bevel 45° bevel 30° open 60° open 90° open
3 1
/ 16
1 1 1 1 2 3 3
/ 4
5 1
/ 16
3 3 2 2 3 4 6
/ 8
7 4
/ 16
1 4 2 2 4 5 7
/ 2
5 6 3 3 4 6 8
/ 8
3 8 4 5 4 7 9
/ 4
7 5 8 5 10 10
/ 8
1 5 11 5 13 22
1
1 / 8 7 11 9 15 27
1 8 11 12 16 32
1 / 4
3
1 / 8 9 15 13 21 36
1 9 18 13 25 40
1 / 2
3
1 / 4 11 21
*Plate thickness for groove welds.
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