XTRACT: A Tool for Axial Force - Ultimate Curvature Interactions

Abstract

XTRACT started as an academic and research tool at the University of California at Berkeley as a program titled UCFyber. At its infancy, UCFyber was the first interactive Microsoft Windows based program that performed moment curvature analysis for reinforce concrete cross sections. The program had the capability of performing realistic analysis of cross sections incorporating the effects of increased strength and ductility of confined concrete as well as nonlinear steel behavior within a graphical environment. While XTRACT has become an invaluable instrument for concrete research within earthquake engineering, it has also evolved to become a production tool for analysis and design of concrete systems within design offices around the World. XTRACT is an important tool for earthquake engineering analysis when a realistic assessment of moment and curvature capacities of a cross section is required. This paper discusses some of the basic analytical features within XTRACT and introduces some innovative uses of the program for seismic assessment of reinforced concrete columns. During seismic excitation of concrete moment resisting frames axial forces vary due to overturning demands. This, in turn, affects the ultimate curvature capacity and consequentially, the seismic displacement capacity of the concrete columns. By generating a plot of axial force verses ultimate curvature, curvature demands can be checked directly for a concrete column within a seismic force resisting frame. This paper outlines the methodology behind the creation of this type of diagram and includes example diagrams for both unconfined and confined rectangular concrete cross sections.