A New Seismic Design Method for Steel Structures

A seismic design methodology for steel building frames which combines the advantages of the well-known force-based and displacement-based seismic design methods in a hybrid force/displacement design scheme is proposed. The method controls structural performance by first transforming user-specified values of the interstorey drift ratio (non-structural damage) and local ductility (structural damage) to a target roof displacement and then calculating the appropriate strength reduction factor for limiting ductility demands associated with the target roof displacement. The main characteristics of the method are: (1) it treats both drift and ductility demands as input variables; (2) it does not use a substitute single degree of freedom system; (3) it makes use of conventional elastic response spectrum analysis and design; (4) it includes the influence of the number of storeys; (5) it recognizes the influence of the type of the lateral load resisting system (moment resisting frame or concentrically braced frame); (6) it recognizes the influence of geometrical (setbacks) or mass irregularities.