Optimum Plastic Design of Moment Resisting Frames Using Mechanism Control

Abstract In this paper, optimum plastic design using mechanism control (PDMC) for steel moment resisting frames (MRFs) is presented. The PDMC method in the solid plastic analysis, by considering the second-order effects, achieve the global mechanism and prevent undesired mechanisms, which leads to decrease the ductility and energy dissipation capacity of structures, is guaranteed. The concept of the PDMC is based on the plastic rotation of columns in developing a mechanism in which for a specified target displacement, the global mechanism has a minimum plastic rotation of columns among all other undesired collapse mechanisms. In terms of involving optimization to the PDMC procedure, two methods are considered: 1) based on the sum of the reduced plastic moment of columns in each story, 2) based on the plastic moment of all members. For both methods, minimum structural weight is obtained by defining a linear programming problem. To show the accuracy of the design procedure, three frames consisting of four, eight, and twelve-story MRFs are designed by two methods, then they evaluated under the pushover and the IDA analyses. The results indicate that the designed frames by the second method have less weight compared with those designed using the first method. However, frames designed by both mentioned methods had high seismic performance and the design goal that is attaining to the global mechanism is achieved.