Page 256 - Handbook of Structural Steel Connection Design and Details

Welded Joint Design and Production

Welded Joint Design and Production 241

Because of the versatility of welding, there is the possibility of configur-
ing the materials in ways in which ductility cannot be achieved. It is
essential that a fundamental understanding of ductility be achieved in
order to ensure ductile behavior in the steel in general, and in the
welded connections in particular.
Unique capabilities of welded designs. Welding is the only method by
which multiple pieces can be made to act in complete unison as one
metallurgical system. Loads can be efficiently transferred through
welded connections, and joints can be made to be 100% efficient.
There are, however, no secondary members in welded designs. Weld
backing, for example, participates in conducting forces through mem-
bers, whether intended or not. The design versatility afforded by the
welding process allows for configuring the material in less than opti-
mum orientations. The constraints associated with other systems
such as bolting or the use of steel castings provide other constraints
that may force compromises for manufacturing but may simultane-
ously optimize the transfer of stress through the members. It is critical,
therefore, that the engineer utilize designs that capitalize upon weld-
ing’s advantages and minimize potential limitations.
Requirements for efficient welded structures. Five elements are present
in any efficient welded structure:
1. Good overall design
2. Good details
3. Good materials
4. Good workmanship
5. Good inspection

Each element of the preceding list is important, and emphasis on one
item will not overcome deficiencies in others. Both the Northridge
and Kobe earthquakes have shown that most of the undesirable
behavior is traceable to deficiencies in one or more of the preceding
areas.

3.9.4 Design of seismically resistant
welded structures

System options. Several systems are available to the designer in
order to achieve seismic resistance, including the eccentrically braced
frame (EBF), concentrically braced frame (CBF), special moment-
resisting frames (SMRF), and base isolation. Of the four mentioned,
only base isolation is expected to reduce demand on the structure.

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