Modified‐modal‐pushover‐based seismic optimum design for steel structures considering life‐cycle cost

A modified‐modal‐pushover‐based optimization technique is presented to design steel moment resisting frame buildings for minimizing the life‐cycle cost based on the framework of performance based earthquake engineering. Modified modal pushover analysis (MMPA) procedure capturing the higher mode effect well is utilized to analyze the inelastic seismic demands of the structures subjected to the considered design earthquakes in terms of the Chinese seismic code for buildings, especially for the medium‐ to high‐rise buildings. Furthermore, the life‐cycle cost is formulated as the summation of the initial material cost and the future expected damage loss, which can be stated as a function of seismic performance levels and their corresponding failure probability by means of a statistical model. Meanwhile, the damage loss is explicitly and continuously expressed by the defined interstory drift index using the fuzzy‐decision theory. Moreover, the powerful adaptive simulated annealing algorithm is applied to solve the discrete optimization problem due to the discreteness of standard steel sections. Finally, a 9‐story planar steel frame is provided to illustrate the effectiveness of the proposed optimization design technique, which achieves not only more cost‐effective design but greatly improves the robustness of the optimum design as well.