جلال اکبری

Force-based and displacement-based seismic design methods are common methods in seismic designing of the structures. Disadvantages of these methods have been led that the researchers introduce combined seismic design methods in recent years. The purpose of this study is to introduce a new combined method called modified earthquake coefficient method. This new method is formed from the combination of the force-based design method that presented in the standard 2800, and the displacement-based method presented in the 360 issue. In the proposed method, the behavior and reflection coefficient factors are determined by considering the actual behavior of the structures and taking into account the analytical periods of them in the calculations process. In order to determine the behavior factor in the modified earthquake coefficient method, the nonlinear static analysis is used. For evaluating the performance of the proposed method in this research, steel moment-resisting frames in the form of three, six and nine-story frames and assuming special ductility for them were designed according to force method, modified earthquake coefficient method and hybrid force/displacement seismic design procedure. Finally, the seismic responses under seven severe earthquake records and Rayleigh damping model and stiffness proportional damping were performed, and the results were compared. The results show that the reduction of the weight in comparison with force method for the studied three, six and nine-story frames in the level of life safety performance are respectively 242, 601 and 840 kg (almost 8 %).