This paper presents a methodology for structural health monitoring (SHM) of existing bridges, designed to operate at progressively detailed levels and capable of detecting multiple structural damage scenarios. The SHM system is tailored based on the potential damage the structure may experience throughout its lifespan. By considering the bridge's structural type, materials, construction technology, and current health conditions, a comprehensive list of possible damage scenarios can be identified. The effects of these scenarios can be effectively characterized and either directly or indirectly monitored through the SHM system. Following a data-driven approach, the acquired static and dynamic data are processed using pre-defined algorithms to evaluate and track key parameters associated with the analyzed scenarios over time. The proposed methodology is applied to an existing bridge equipped with an SHM system, with a focus on structural scenarios to demonstrate its practical implementation and effectiveness.