Prediction of post-fire seismic performance of reinforced concrete frames

Due to the importance of evaluating the seismic behavior of structures after a fire, a numerical study was conducted on RC frames using the detailed finite element method. The simulation process consists of two separate steps. The first step is heat transfer analysis to estimate heat distribution in the various elements of RC frames, and the second step is evaluating the post-fire seismic performance of the frames using thermal-mechanical analysis. The test specimens used to verify the proposed FE model include two RC frames with different beam-column bending capacity ratios, which are in two different conditions, including the specimens at ambient temperature as control specimens and fired specimens inside of the furnace chamber. In the heat transfer analysis step, the sensitivity of responses to two effective parameters, including the moisture content and the emissivity of the concrete surface has been investigated. In the post-fire analysis, among the various models presented for the post-fire behavior of concrete, three stress-strain models were selected for cyclic analysis of RC frames and the results were compared with the test data. Also, the bond-slip behavior of the concrete-steel interface has been simulated using the equivalent springs technique. It was seen from the comparison of the numerical results with the test data, that the proposed model accurately estimates the resistance and the dissipated energy of frames in each cycle. In addition, parametric studies showed that every 30 min increase in the fire duration based on the ISO 834 standard curve causes a 10% decrease in post-fire seismic resistance compared to the control specimen.