Seismic Design of Bolted Steel Moment Resisting Frames 95

Moment-resisting frames (MRFs) are structures that resist applied forces
primarily by bending of their members and connections. MRFs can provide large
open spaces without the obstruction usually caused by braces or shear walls. In
addition, because of their flexibility and relatively long period of vibration, MRFs
usually attract smaller seismic forces than the comparable braced or shear wall
systems.
Since the early days of riveting, steel MRFs have been very popular in
building construction. Many structures including the monumental high-rises of
the late nineteen and early twentieth centuries have been built using riveted steel
MRFs. On the west coast, many turn-of-the-century tall buildings in San
Francisco have riveted steel MRFs. Since the 1960's, with the advent of highstrength
bolting as well as welding technologies, bolted steel moment-resisting
frames (BMRFs) and welded steel moment-resisting frames (WMRFs) have been
one of the main structural systems used in office and residential buildings.
In recent years because of ease of fabrication and design and for
economical reasons, most of the steel moment-res]sting frames used in seismic
areas such as California have had welded moment connections. However,
welded steel moment-resisting frames are only one of the many possibilities of
steel moment frames.
The main purpose of this report is to present information on the seismic
design of steel rigid moment-resisting frames with bolted or bolted/welded
connections. Today, there is sufficient information and experience that bolted
and bolted/welded steel moment-resisting frames can be designed and
fabricated to provide safe and economical structural systems for seismic regions.
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