Document Type



Master of Science


Structural Engineering

First Adviser

Richard Sause


This research explores the use of the Conditional Mean Spectrum for selecting and conditioning ground motion records for the seismic analysis of nonlinear systems with an emphasis on self-centering systems. Self-centering systems are an innovative type of seismic lateral force-resisting system which can reduce the post-earthquake damage sustained by building structures. Self-centering systems may experience greater lateral displacements than conventional systems, resulting in more significant period elongation. The period elongation may cause self-centering systems to be more sensitive to ground motions selected and conditioned on periods other than the initial natural period. Specifically, this study focuses on the influence of conditioning period with respect to the displacement-ductility demands on self-centering and conventional systems. During the study, nonlinear response spectra for 25 different single-degree-of-freedom models were evaluated over a range of 60 natural periods. Conditional Mean Spectra were constructed for ten logarithmically spaced conditioning periods. Twenty ground motions were selected and amplitude scaled to match each of these ten Conditional Mean Spectra. The results show that conditioning periods greater than the initial natural period of the structure produced the largest ductility demands. A conditioning period ratio was defined as the ratio of the conditioning period which produces the largest ductility demand to the initial natural period. The results show that the conditioning period ratio is strongly dependent on the strength reduction factor and energy dissipation, and approximately independent of the initial natural period. The effects of variation of the post-yielding stiffness are not considered. For a given strength reduction factor and energy dissipation, the conditioning period ratio appears to be constant. Conventional bilinear elasto-plastic systems exhibited a period ratio close to unity for strength reduction factors greater than 2. Although the results suggest a relationship between the conditioning period and the nonlinear characteristics of self-centering and conventional systems, further study is required due to the limited number of conditioning periods considered in the present study.