Optimal Design and Performance Assessment of Viscous Dampers in Steel Frames Based on Life Cycle Cost

In recent years, it is tried to express the expected performance of structures as financial and social measures. In this study, an algorithm for optimal design of viscous dampers with the goal of achieving minimum total cost is presented. For this purpose, an appropriate cost model to determine the initial cost of equipping structures with viscous dampers has been presented and the expected costs of the structure due to possible earthquakes over its life cycle have been estimated using life cycle cost analysis (LCCA). The results of this analysis have been used in an optimization algorithm with the aim of achieving minimum total cost of structures. To evaluate the seismic behavior of structures, the Endurance Time (ET) method is used as a dynamic analysis method which requires much less computation effort than conventional time history methods. In this regard, three moment frames with 3,7 and 15 stories having weakness in initial design are modeled nonlinearly, and then, using genetic algorithm the optimum arrangement of linear and nonlinear viscous dampers along with the damping exponent (Alpha) is acquired. Two closed form methods have also been used for the design of viscous dampers, namely energy-based damping design and direct displacement design. Finally, the performance of the structures has been evaluated under 12 far-field and 12 near fault ground motion records.