A seismic moment frame comprises of a rectangular system of rigidly connected columns and beams that resist moment and shear forces developed during earthquake ground shaking. Seismic standards typically consider the system extremely ductile and assign it the highest allowable response modifcation coeffcient.
It is one of only few systems permitted in SDCs D, E, and F for buildings exceeding 160ft in height. Because earthquake motions can induce multiple inelastic displacement cycles, special proportioning and qualifcation requirements are essential for robust moment frame performance.
Although the steel special moment frame (SMF) is a relatively recent development in building codes, steel frames have been in use for more than 100 years, dating to the earliest use of structural steel in building construction. Framing in these early structures typically utilized “H” shapes built up from plate, “L” and “Z” sections. The connections typically incorporated large stiffened triangular gusset plates, joined to the beams and columns with angles and rivets.
The basic construction style remained popular for high-rise construction through the 1930s. By the early 1900s, rolled “H” shape sections began to see increasing use in place of the built-up sections, in particular for lighter framing. Many tall structures including the Empire State Building in New York, for many years the world’s tallest structure, are of this construction type.
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