On the modal incremental dynamic analysis of reinforced concrete structures, using a trilinear idealization model

In order to estimate the seismic demands at the performance level, the inelastic behavior of concrete structures should be considered. Incremental dynamic analysis (IDA) based on a nonlinear response time history analysis (NL-RHA) is considered to be the most accurate method in seismic demand calculations. However, modal incremental dynamic analysis (MIDA), based on the equivalent single-degree-of-freedom (SDF) oscillator, is also often used in studying structural engineering performances. As the MIDA method has usually not been applied to reinforced concrete (RC) structures, in this study an attempt is made to investigate the performances of RC frames and to compare the results obtained through the MIDA against those obtained from exact IDA. Furthermore, an innovative suggestion on approximated pushover curves of the corresponding SDF model, by means of a trilinear idealization representation, is also offered. For this purpose, an eight-story concrete frame subjected to 30 different earthquake records is studied with the trilinear idealization model, and the damage measures, important for the seismic vulnerability of buildings, such as the maximum displacement and the interstory drift ratio, are considered. Comparison of the results has shown reasonable and/or acceptable precision and reveals good agreement of the MIDA method with the new idealization behavior model for concrete frames.