Multi-objective seismic design method for ensuring beam-hinging mechanism in steel frames

Previous research efforts have shown that the column-beam flexural strength ratios of joints in moment resisting steel frames should be higher than 1.0 or even 2.0 for a beam-hinging collapse mechanism. However, it has been pointed out that, in order to prevent a weak story mechanism in a structure, it is not practical to use a specific single value as a limit for the column-beam flexural strength ratio for all joints of a structure. Therefore, an optimal design technique is needed to determine the column-beam flexural strength ratios for joints in a structure. In this paper, a multi-objective seismic design method for ensuring beam-hinging mechanism in steel moment resisting frame structures is presented and applied to optimal seismic design of well-known steel moment frames. In addition to the constraint for ensuring beam-hinging mechanism, the relationship between the structural cost and the energy dissipation capacity of structures is provided by considering the two conflicting objective functions. In order to select the best design among the candidate designs, as a guide for structural engineers, a simple rule is presented in the form of dissipated energy density defined by the ratio of the energy dissipation capacity to the structural weight. (C) 2012 Published by Elsevier Ltd.