Nonlinear Seismic Design of Multistory Frames

Abstract
A five-step, computer-aided design procedure representing a significant change from current seismic design practices is proposed.In the first step, the ‘design earthquake’ and the safety and serviceability criteria are established, and appropriate values of a damping coefficient and displacement ductility factor are assumed. An iterative preliminary analysis procedure, centered around specified values of a seismic coefficient and a drift index, is used to determine the design story shears using modal analysis.Then, a preliminary design is carried out using a simplified story-wise optimization procedure. This is followed by inelastic static and dynamic analyses of the design. The maximum values of story shears and ductilities and their overall pattern, so obtained, are compared against those used initially. The procedure is repeated until a satisfactory agreement is obtained and the final design story shears are determined. In the fourth step, these shears are used to attain the final optimum design through a procedure similar to that used in the preliminary design, but using an improved story subassemblage and a more formal linear optimization technique.Finally, the reliability of the optimum design is evaluated by determining its nonlinear response to severe earthquakes and its serviceability. The design procedure is demonstrated on a 10-story 3-bay frame.