Steel Special Moment Frames: A Historic Perspective

June 29, 2010
Publication: Structure Magazine
Author(s): Ronald Hamburger Scott M. Adan

Many modern buildings use steel special moment frames for their seismic lateral force-resisting system. A moment frame is comprised of a rectangular system of rigidly connected columns and beams that resist moment and shear forces developed during earthquake ground shaking. The building code considers the system extremely ductile and assigns it the highest allowable response modification coefficient. It is one of the only few systems permitted in Seismic Design Categories D, E and F for buildings exceeding 160 feet in height. With the absence of diagonal braces or structural walls, the system facilitates architectural versatility for interior space layout and aesthetic exterior expression. Because earthquake motions can induce multiple inelastic displacement cycles, special proportioning and qualification requirements are essential for robust moment frame performance. The numerous interrelated code provisions that address these special requirements are not necessarily arranged in a logical sequence, making their application challenging for all but the most experienced designers.

Services: Structural Design