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The most important feature of the behavior factor is that it allows the structural designer to be able to evaluate the structural seismic demand, using an elastic analysis, based on force-based principles quickly. In most seismic codes, this coefficient is merely dependent on the type of lateral resistance system and is introduced with a fixed number. However, there is a relationship between the behavior factor, ductility (performance level), structural geometric properties, and type of earthquake (near and far). In this paper, a new and accurate correlation is attempted to predict the behavior factor (q) of EBF steel frames, under near-fault earthquakes, using the genetic algorithm (GA). For this purpose, a databank consisting of 12960 data is created. To establish different geometrical properties of models, 3−, 6−, 9−, 12−, 15, and 20− story steel EBF frames were considered with 3 different types of link beam, 3 different types of column stiffness, and 3 different types of brace slenderness. Using nonlinear time history under 20 near-fault earthquake, all models were analyzed to reach 4 different performance levels. 6769 data were used as GA training data. Moreover, to validate the correlation, 2257 data were used as test data for calculating mean squared error (MSE) and correlation coefficient (R) between the predicted values of (q) and the real values. In addition, the MSE and R were calculated for correlation in the train and test data. Also, the comparison of the response of maximum inelastic displacement of 5 stories EBF from the proposed correlation and the mean inelastic time-history analysis confirms the accuracy of the estimate relationship.

In this article, it is intended to find a proper spectral Intensity Measure parameter (IM), using Bayesian statistics, to estimate the seismic demand of steel moment-resisting frames in such a way that applying this IM to both parts of seismic demand estimation, i.e. the probabilistic seismic demand model and collapse fragility curve, leads to a precise estimation for all frames with different heights. After results show that finding such IM parameter is impossible among spectral accelerations individually, due to effects of different modes and nonlinear behavior of structures, the area under the spectral acceleration is introduced as a new IM. Considering the results of incremental dynamic analysis of frames subjected to 80 selected ground motion records, on the condition of selecting a suitable interval of periods, this new IM can reduce the dispersion of results. This interval can be defined as [αTm-βT1], in which T1 and Tm are the first period and the period with 95% mass participation and α and β are two modification coefficients.