Optimal DDBD procedure for designing steel structures with nonlinear fluid viscous dampers

This paper presents an optimal direct displacement-based design (DDBD) procedure for designing steel moment-resisting frames equipped with nonlinear fluid viscous dampers (FVDs). The design method is based on defining an optimization problem to determine the optimal distribution of FVDs along the height of the structure to achieve a desired added damping ratio by FVDs with the minimization of total damping coefficient of dampers. The optimization problem is solved using the distributed genetic algorithm (DGA) to determine the damping coefficient of each FVD. For numerical illustration, the proposed optimal DDBD procedure has been used to design four moment-resisting steel frames of 4, 8, 12, and 20-storey equipped with linear and nonlinear FVDs. The effectiveness of the proposed method has then been evaluated by performing nonlinear time history analysis on the considered frames under 20 earthquake records. Moreover, the effect of the displacement profile on the efficiency of the proposed design method has been discussed. The results of extensive numerical simulations show that using the proposed method for optimal distribution of the dampers in DDBD procedure has been considerably effective in reducing the total damping coefficient and maximum force of the dampers while satisfying the expected performance criteria. It has also been found that designing nonlinear FVDs based on the proposed optimal DDBD method have resulted in a significant reduction in the maximum damper force compared to linear FVDs.