AbstractReinforced concrete (RC) structures with weak or soft stories have exhibited poor seismic performance in several past earthquakes, primarily due to high seismic force and deformation demands on the columns in these soft stories. This study presents a strategy to improve the seismic performance of these structures by using structural steel–reinforced concrete (SRC) columns. A design methodology using the energy-balance concept was proposed for the RC-SRC hybrid structures. A five-story study frame with conventional RC as well as SRC columns was numerically modelled in the computer software OpenSees to assess seismic collapse performance. The nonlinear modelling technique was validated by comparing the predicted cyclic force-deformation behavior with the past test results. Nonlinear cyclic pushover and dynamic time-history analyses were conducted to compare the seismic performance of the RC and SRC frames. Incremental dynamic analyses (IDAs) were conducted to predict their collapse probabilities and derive their collapse fragility curves. The results of the static and dynamic analysis show a significant improvement in the seismic performance of the hybrid frame over the original RC frame.

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