The scaled nonlinear dynamic procedure

Although nonlinear static procedures (NSPs) have become widely accepted for use in seismic design and evaluation in recent years, their accuracy is poor for response quantities that are significantly affected by the vibration of multiple degrees of freedom (termed MDOF effects). In recent work performed for the ATC-55 project, a design-oriented approach, called the scaled nonlinear dynamic procedure (Scaled NDP), was identified for determining such response quantities for nonlinear systems. The Scaled NDP provides an alternative to current code approaches for scaling ground motions for dynamic analyses and is readily used in performance-based seismic design and evaluation. The Scaled NDP appears to provide a valid basis for establishing force quantities at stated levels of confidence and provides an indication of deformation demands for use in design and evaluation. The results can be used to determine the strengths required of members in order to ensure that ductile behavior develops, and to evaluate the deformation performance of a given design.