Optimal Properties of Nonlinear Viscous Dampers in Steel Structures Considering the Life Cycle Cost

Recent studies demonstrated that high-frequency earthquakes have the most effect on the economic losses during seismic events. However, code-based seismic design criteria mainly aim to provide the occupants' life safety. In this regard, code-compliant structures may result in significant economic losses during their life span. These damages contribute to the higher repair costs and lengthy functional disruptions of these structures. Improving the seismic behaviour of the structures by control devices could be one of the most efficient solutions. On this subject, applying fluid viscous dampers (FVDs) is an economical and reliable method. Optimizing the properties of these devices contributes to more efficient seismic behaviour of the structures. In this study, the key design parameters of viscous dampers, including damping coefficient and velocity exponent, are considered as optimization variables to achieve minimum life cycle cost (LCC) using the genetic algorithm (GA). To investigate the efficiency of the proposed approach, four-, eight- and twelve-story structures in high-seismic regions are investigated to consider different assumptions. The Endurance Time method (ETM) is adopted to conduct nonlinear analysis due to its high computational cost-efficiency and reliability. The results show that the nonlinear viscous dampers would decrease the total seismic loss of the structures by up to 40% in comparison with linear dampers. The optimal amount of velocity exponent is also obtained as a function of variation with the height and seismic region of the structures.