Direct displacement-based seismic design

Abstract

There has been considerable discussion recently in New Zealand about the relative merits of displacement-based, and displacement-focused force-based seismic design. This paper puts the case for direct displacement-based seismic design. It is shown that the emphasis on secant stiffness to maximum displacement, rather than initial stiffness (as in force-based seismic design) is important for rational force-distribution to different seismic-resisting structural elements, and in most cases obviates the need for iteration in the design process, which is inherent in displacement-focused force-based seismic design. It is shown that the influence of hysteretic characteristics has been underestimated in recent force-based studies. These assertions are supported by results of recent analytical studies, which have included refinement of ductility/equivalent-viscous damping relationships, and an examination of the important (and largely ignored) role of “elastic” damping in inelastic time-history analyses.