Seismic Behavior of Steel-Concrete Composite Frame Structures and Design Practice in the United States

Steel-concrete composite frames have been shown to be a sensible option for use as the primary seismic force resisting system of building structures. However, there remains little data to justify the structural system performance factors (i.e., R, C_d, and Ω_o) that characterize the overstrength and ductility of these systems, which are a vital component of successful design in the United States. Based on a suite of new finite element formulations, this work investigates the behavior of composite moment and braced frames under seismic loading and develops rational system performance factors. A set of archetype frames, selected to be representative of the range of frames seen in practice, were designed according to current design specifications. Nonlinear static pushover and transient dynamic analyses were performed on the frames to generate the statistical data on the seismic response from which the performance factors are 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.