Investigation of seismic Fragility and collapse capacity of RC Moment Frames Considering the increase of stiffness of the column relative to the beam under far and near field earthquakes

In the present research, the seismic fragility and collapse capacity of concrete moment frames have been investigated by considering different ratios for the weak beam-strong column rule in the optimization process in the performance-based design framework. In order to implement performance-based optimization, the center of mass metaheuristic algorithm has been applied in this research. The philosophy of design approach based on performance and even traditional design methods allows the structure to suffer damage facing strong and relatively strong earthquakes. Therefore, in order to estimate the level of safety of the structure against earthquakes, it seems necessary to use quantitative indicators of seismic safety and the collapse capacity of the structure. In order to predict the collapse capacity of each optimal structure, using incremental dynamic analysis, the modified collapse safety margin ratio under far and near fault earthquakes has been calculated. Two examples, 3-span three and six floor frames have been studied in this research, which are designed in the performance-based optimization framework and considering the coefficients of 0.8, 1.2 and 1.6 to control the weak beam-strong column rule in the optimization process. The results indicate that increasing the rigidity of the column compared to the beam in this research actually affects the ductility of the structure, and by choosing structures with greater rigidity of the column compared to the beam, it leads to an increase in the collapse capacity and a decrease in the fragility of the structure.