This paper investigates the optimal design of steel moment-resisting frame (MRF) buildings, with and without metallic yielding dampers, using a life-cycle cost (LCC)-based optimal design process. The aim is to minimize the LCC as the design criterion, which includes construction cost and the loss of lifetime seismic consequences. The study employs the endurance time (ET) method for structural response analysis and the FEMA P-58 procedure for seismic loss assessment. Four design approaches are examined: (1) typical code-based design of an existing MRF without damper, (2) optimal LCC-based design of a new MRF without damper, (3) optimal LCC-based design of an existing MRF equipped with damper, and (4) optimal LCC-based design of a new MRF equipped with damper. In the third scenario, only the damper properties are optimized, whereas in the fourth scenario, both the frame and damper properties are optimized together. The main contribution of this study is the simultaneous comparison of the design outcomes from the four aforementioned design approaches. The results indicate that LCC-based re-designed structures can effectively reduce costs compared to code-based designs. The best results were achieved by incorporating metallic dampers. Moreover, incorporating dampers also reduced the construction cost for the LCC-based re-designed cases. Based on the results, when dealing with similar scenarios, adding dampers to an existing frame can be sufficient, eliminating the need to redesign both the damper and frame together.

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