Keywords: steel moment frame, drift design, optimization, column-to-beam strength ratio, resizing.

This paper proposes an optimum drift design model, using linear-static analysis, which can control the elastic and inelastic performance of the steel moment frames. The proposed method is formulated as a problem that minimizes the lateral displacement at the top of the building, while also satisfying the constraints on the total structural weight and the column-to-beam strength ratio at the joints. This can increase the stiffness of buildings without increasing the structural weight, because the resizing of the size of the elements is based on the displacement participation factor (DPF) calculated by the unit-load method. In other words, the structural weight of each member is efficiently redistributed according to its displacement participation. At the same time, this constrains the column-to-beam strength ratio at the joints, which prevents excessive redistribution of the weight of the columns to the weight of the beams. Hence, the inelastic performance of the structure can be controlled.

The three-storey steel moment frame example was used to verify the proposed model. When the structure was redesigned, with just the displacement participation factor, with no consideration for the flexural strength ratio, the initial stiffness was increased, but inelastic performance, such as energy dissipation capacity decreased. However when the flexural strength ratio for joints were considered simultaneously, the initial stiffness showed a smaller increase, but inelastic performance was enhanced. In other words, the proposed model was confirmed to be effective in controlling the initial stiffness and energy dissipation capacity of the structure.

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