Optimal seismic retrofit of fractional viscoelastic dampers for minimum life-cycle cost of retrofitted steel frames

Previous studies have shown that fractional derivative models present a plausible level of accuracy when it comes to capturing the behavior of viscoelastic dampers due to being capable of expressing the effects of excitation frequency and ambient temperature in viscoelastic damper parameters. Considering the possibility of earthquake occurrence during a structure lifetime, minimizing the life-cycle cost of a building is a practical way of optimizing the seismic design or retrofit plan and performance of the structure. In this paper, the total life-cycle cost of a structure with fractional viscoelastic dampers is chosen as the objective of an optimization problem while considering the effects of the changes in the ambient temperature and uncertainty related to the ground motion excitation which are the decisive parameters in the life-cycle cost analysis. The results for a 5-story steel frame show lower total life-cycle cost, initial cost, and story drift for the optimized structure compared to one with uniform distribution of dampers. Also, more use of dampers in optimized structure with life-cycle cost minimization objective, compared to a structure designed to minimize the cost of the dampers, has led to a significant reduction in the expected life-cycle damage costs.