Civil Engineering Association

EVALUATION OF SEISMIC DEFORMATION DEMANDS USING NON- LINEAR PROCEDURES IN MULTISTORY STEEL AND CONCRETE MOMENT FRAMES

A key component of performance-based seismic evaluation is the estimation of seismic demands. In FEMA-356 (FEMA, 2000b), which is now recognized as the model for future performance-based seismic codes in the US, these demands are evaluated at the component level in terms of ductility demands or plastic rotations when using non-linear procedures. Since acceptance criteria for various performance objectives are assessed in terms of local component demands, it is essential that a rational basis be established for determining such demands. Of the non-linear procedures advocated in FEMA-356,
pushover procedures are becoming increasingly popular in engineering practice. However, there are still several unresolved issues in identifying appropriate lateral load patterns to be used in a pushover procedure. This paper investigates the correlation between demand estimates for various lateral load patterns used in non-linear static analysis. It also examines the rationale for using component demands over story and system demands. Results reported in the paper are based on a comprehensive set of pushover and non-linear time-history analyses carried out on eight- and twelve-story steel and concrete moment frames. Findings from this study point to inconsistencies in the demands predicted by different
lateral load patterns when using pushover analysis and also highlight some issues in the current understanding of local demand estimates using FEMA-based procedures.