Seismic Safety and United States Design Practice for Steel-concrete Composite Frame Structures

In United States design practice, three system performance factors (R, Cd, and o) characterize the inelastic behavior of structures and are a crucial component of common elastic design methodologies. However, for steel-concrete composite frame systems these factors have been selected based on comparisons to more traditional and well-studied reinforced concrete and structural steel frame systems, without significant quantitative justification. In this study, the seismic behavior of steel-concrete composite moment and braced frames is investigated and rational system performance factors are developed. A set of archetype frames, selected to be representative of the range of frames seen in practice, were designed according to current design specifications. Using a suite of new finite element formulations for composite systems, nonlinear static pushover and transient dynamic analyses were performed on the frames. The results of the analyses served as statistical data on the seismic response from which the performance factors were quantified. The results from this investigation enable a better understanding of the variability in collapse performance of composite frame systems and will facilitate more effective designs of these systems.