HYBRID MOMENT RESISTING STEEL FRAMES

A new type of moment resisting steel frame, called a Hybrid Moment Resisting Frame, is described. Unlike a typical moment frame, where all member sizes and connection details fit a specific set of rules (e.g. for a special moment frame), the Hybrid Frame contains members and connections with a variety of detailing rules, including those typically associated with ordinary (OMF), intermediate (IMF), and special moment frames (SMF). Elements that have special detailing are designed to yield at force levels well below the design basis earthquake, and thereby provide some inelastic energy dissipation that helps to control dynamic amplification. Elements with ordinary detailing are designed to remain elastic during the design basis earthquake, and to provide enough positive stiffness to counteract P-delta effects. The resulting system is expected to perform better than the traditional special moment frame, and to be more economical than the special moment frame because a limited number of elements and connections have special detailing. The behavior of the system is demonstrated through incremental nonlinear dynamic response history analysis.