Several significant seismic events have highlighted the need to assess the seismic vulnerability of critical infrastructures, particularly high-voltage grids, which are crucial for maintaining power supply in emergency scenarios. Despite the installation of advanced nonlinear energy dissipation devices to protect against seismic actions, design documentation is often inadequate, leaving gaps in accurately predicting system behavior. This paper proposes a simplified approach to effectively assess the seismic vulnerability of articulated structures exhibiting nonlinear behavior. A by-pass switch equipped with four wire rope dampers has been subjected to seismic qualification tests at the L.E.D.A. (Laboratory of Earthquake Engineering and Dynamic Analysis) Research Centre of the University of Enna Kore. A Finite Element Method (FEM) model has been developed using displacement and acceleration data, followed by a two-step optimization process using a novel optimisation technique, called Continuous Particle Swarm Optimisation. In the first step, the frequencies and damping were accurately approximated to the experimental values, but the comparison in terms of displacement results remained imprecise. After the optimization of the nonlinear parameters, the dynamic response showed a good degree of agreement with the experimental data in terms of frequency and damping, as well as in terms of displacements and accelerations. This provides a reliable framework for developing simplified and validated FEMs for complex structures with nonlinear dampers.