The Friction Pendulum System (FPS) is one of the most widely used sliding-based energy dissipation devices for reducing damage in structures. In this system, the motion of the slider due to external forces, along with its contact with concave or spherical surfaces, generates a friction force. On the other hand, research has shown that variations in normal force and sliding velocity are two critical factors influencing the friction parameter. Notably, changes in the friction parameter can significantly impact FPS performance and, consequently, the response of the structure isolated by this system. Vertical force also affects the coefficient of friction, attributed to variations in the normal force. Therefore, this subtle factor can strongly affect the responses of structures that use friction-dependent devices like FPSs. This study investigates the nonlinear response of a three-span continuous concrete I-girder bridge equipped with FPS. A sinusoidal dynamic load was generated and applied to the structure using Opensees platform. Employing nonlinear time-history analysis, structural responses were obtained and analyzed, including axial force in columns, isolator force, isolator displacement, and column displacement. The results show that variations in vertical force significantly influence the nonlinear dynamic behavior of both the bridge and the isolator, demonstrating that friction and vertical force interactions play a crucial role in the seismic response of FPS-isolated structures.