Minimum column-to-beam strength ratios for beam-hinge mechanisms based on multi-objective seismic design

The current strong-column weak-beam design criterion presents a single value as the acceptance limit of strength ratios for Special Moment Resisting Frames (SMRFs). However, previous research efforts have shown that the required column-beam flexural strength ratios of joints in SMRFs vary with the factors such as the height of frames. Therefore, in this paper, the multi-objective seismic design method based on nonlinear static analysis is proposed and applied to find optimal column-to-beam strength ratios required for ensuring the beam-hinge mechanism. In this formulation, the optimal method is to minimize the two objective functions of the structural weight as well as the column-to-beam strength ratio while satisfying the constraints. Based on multiple Pareto-optimal solutions with beam-hinge mechanisms, the relationship between the structural weights and optimal strength ratios is provided. Using the well-known two moment resisting example structures, instead of suggesting a specific single value as a limit for the column-beam flexural strength ratio, a common tendency is identified through investigating the relationships between optimal strength ratios and structural weights.