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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, construction of the most precise possible probabilistic model for the estimation of seismic demand in steel moment-resisting frames, with different heights, using the Bayesian Statistic, is attempted. In this study, after proving that the best form for defining the model is a linear combination of the logarithm of Intensity Measure (IM) parameter, the best IM was selected based on the practicality, efficiency and sufficiency of models. Some particular results show that the precision of models with one single IM depends on the number of stories in the structure, so no model including the current one, i.e. the one with spectral acceleration in the first period as IM can be introduced as the best model of all frames with whatever height. Since making use of a combined IM including two spectral values as a solution is not practical due to the extreme difficulty of producing a multiple parameter seismic hazard curve, in this study it was shown that the best possible method for construction of the model is the use of two single IMs, i.e. the best model to cover all structural heights is the one with a linear combination of the logarithm of spectral acceleration at the first and second periods.