Page 251 - Handbook of Structural Steel Connection Design and Details

Welded Joint Design and Production

236 Chapter Three

second phase of SAC research, also funded by FEMA, began in 1996
and was expected to continue through 1998. Additional information is
expected from these studies.
The principles contained in this section are generally based upon
well-founded engineering principles. However, not all of the recom-
mendations based upon these principles have been subject to testing.
Application of this information to a specific project is necessarily the
responsibility of the engineer of record.

3.9.2 General review of welding
engineering principles
For dynamically loaded structures, attention to detail is critical. This
applies equally to high-cycle fatigue loading, short-duration abrupt
impact loading, and seismic loading. The following constitutes a
review of basic welding engineering principles that apply to all con-
struction, but particularly to seismic applications.

Transfer of loads. All welds are not evenly loaded. This applies to
weld groups that are subject to bending as well as those subject to
variable loads along their length. A less obvious situation occurs when
steels of different geometries are joined by welding. A rule of thumb is
to assume the transfer of force takes place from one member, through
the weld, to the member that lies parallel to the force that is applied.
Several examples are illustrated in Fig. 3.23. For most simple static
loading applications, redistribution of stress throughout the member
accommodates the variable loading levels. For dynamically loaded
members, however, this is an issue that must be carefully assessed in
the design. The addition of stiffeners or continuity plates to column
webs helps to unify the distribution of stress across the groove weld.
Notice that the distribution of stress across the groove weld joining a
beam to an I-shaped column is just opposite that of the same beam
joined to a box column.
Minimize weld volumes. A good principle of welded design is to always
use the least amount of weld metal possible for a given application.
Not only does this have sound economic implications, but it reduces
the level of residual stress in the connection. All hot expanded metals
will shrink as they cool, inducing residual stresses in the connection.
By reducing the volume of weld metal, these tendencies can be mini-
mized. Details that will minimize weld volumes for groove welds gen-
erally involve minimum root openings, minimum included angles,
and the use of double-sided joints. Taken to the extreme, however,
these approaches may violate the principles outlined in “Provide
Ample Access for Welding” section. By reducing the shrinkage stress,
distortion and cracking tendencies can be minimized.

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