Page 238 - Handbook of Structural Steel Connection Design and Details

Welded Joint Design and Production

Welded Joint Design and Production 223

that the area of the welded connection now becomes just the length of
the weld.
Instead of trying to determine the stress on the weld (this cannot be
done unless the weld size is known), the problem becomes a much
simpler one of determining the force on the weld.

3.6.7 Use standard formulas to find force
on weld

When the weld is treated as a line by inserting the property of the
welded connection into the standard design formula used for that par-
ticular type of load (see Table 3.1), the force on the weld may be found
in terms of pounds per lineal inch of weld.
For example, for bending:
Standard design formula Same formula used for weld
(bending stress) (treating weld as a line)
M M
f
S S
w
Normally the use of these standard design formulas results in a
unit stress, in pounds per square inch; however, when the weld is
treated as a line, these formulas result in a force on the weld, in
pounds per lineal inch.
For secondary welds, the weld is not treated as a line, but standard
design formulas are used to find the force on the weld, in pounds per
lineal inch.
In problems involving bending or twisting loads, Table 3.2 is used.
It contains the section modulus, S , and polar moment of inertia, J ,
w w
of some 13 typical welded connections with the weld treated as a line.
For any given connection, two dimensions are needed, width b and
depth d.
Section modulus S is used for welds subjected to bending loads,
w
and polar moment of inertia J for twisting loads.
w
Section moduli S from these formulas are for maximum force at
w
the top as well as the bottom portions of the welded connections. For
the unsymmetrical connections shown in the table, maximum bend-
ing force is at the bottom.
If there is more than one force applied to the weld, these are found
and combined together. All forces which are combined (vectorially
added) must occur at the same position in the welded joint.
Calculating weld size for longitudinal welds. Longitudinal welds con-
stitute the majority of the welding performed in many types of con-
struction and hence justify special emphasis. These include the

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