Page 249 - Handbook of Structural Steel Connection Design and Details

Welded Joint Design and Production

234 Chapter Three

Preset or precamber parts before welding: Parts to be joined may be
preset or precambered before welding. When weld shrinkage causes
distortion, the parts will be drawn back into proper alignment.

3.9 Special Welding Issues for Seismically
Resistant Structures

3.9.1 Introduction and background
Steel is an inherently forgiving material, and welded construction is
a highly efficient, direct method by which several members can be
made to function as one. For statically loaded structures, the inher-
ent ductility associated with steel allows the material to compensate
for deficiencies in design, materials, and fabrication. For structures
containing deficiencies in one or more of these three areas that are
subject to cyclical loading, the repeated plastic (or inelastic) defor-
mations can lead to fatigue failure when enough cycles are present.
Fabrication of components such as bridges and crane rail supports is
therefore more sensitive to deficiencies in design, materials, and
fabrication than is fabrication of statically loaded structures. In a
similar manner, welded structures subject to seismic loads are sen-
sitive to these three issues as well. This section addresses those
issues that are necessary to improve the seismic resistance of welded
steel structures.
In addition to providing a concise summary of those items that
should be considered in the design, fabrication, and erection of steel
buildings subject to seismic loading, these items have been separated
from the requirements in the body of this book in order to avoid the
potential introduction of the conservative provisions of this chapter
into requirements for structures subject to standard wind and gravity
loads. Just as it would be inappropriate, and uneconomical, to
impose on all buildings the requirements for bridge fabrication, so it
would be undesirable to see these requirements for fabrication in
seismic zones automatically transmitted to all structures. The cost
increases without any obvious improvement in structure perfor-
mance would be a disservice to the industry and ultimately the owners
of these structures.
The principles presented in Chap. 5 generally apply to seismic con-
struction as well, and the importance of conforming to these princi-
ples is even more significant for seismic construction. The very low
levels of variable stress typically associated with structures subject to
cyclical loading are significantly different from the inelastic loads
imposed by an earthquake. Nevertheless, many of the details as they
relate to weld backing, weld quality issues, and desirable details are
relevant to seismically loaded structures. Chapter 3 provides insight

Downloaded from Digital Engineering Library @ McGraw-Hill (www.accessengineeringlibrary.com)
Copyright © 2009 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.