A Simplified Method for the Preliminary Assessment of the Optimal Damping Ratio of Dissipative Exoskeletons

Steel exoskeletons have emerged as an effective solution for the seismic retrofit of existing buildings, particularly for strategic facilities where rapid, non-invasive interventions are required. When equipped with dissipative devices, these systems can reduce seismic demand through energy dissipation rather than stiffness increase alone, potentially leading to more efficient and economical designs. However, the preliminary design of dissipative exoskeletons remains complex, mainly due to the nonlinear behavior of damping devices and the high computational effort associated with nonlinear dynamic analyses. This study proposes an automated optimization framework for the preliminary design of dissipative steel exoskeletons. A simplified methodology is adopted to correlate the nonlinear damping coefficient of fluid-viscous dampers with an equivalent damping ratio used in linear dynamic analyses, allowing the replacement of nonlinear time-history simulations with spectrum-based analyses. This approach drastically reduces computational time, making it suitable for optimization purposes. A Genetic Algorithm is implemented to determine the optimal exoskeleton layout, member sizing, and damping capacity by minimizing the total intervention cost under drift and strength constraints. The results demonstrate that maximizing the dissipative contribution while reducing steel consumption leads to the most cost-effective solution, satisfying all performance requirements. The proposed framework provides a practical and computationally efficient tool for the early-stage design of dissipative exoskeleton retrofits.