Structural glass represents a relatively innovative and not well-known solution for constructions, where it is largely used for facades, roofs, footbridges, etc. There, multiple (sandwich) glass members can interact with traditional building materials, and should offer appropriate fail-safe performances, within the full life time. However, severe operational conditions, or extreme loads, can increase the intrinsic vulnerability glazing systems. In this paper, the dynamic characterization and damage diagnostic assessment of an existing glass footbridge is carried out, based on Operational Modal Analysis (OMA) techniques.