For decades, the vibration performance of pedestrian structures, like footbridges and floors, has attracted the attention of researchers. According to the literature, specific vibration performances must be satisfied, depending on the class of use, structural typology and material composition of a given pedestrian system. Additional design issues, however, may derive from the presence of structural components that can be susceptible to unfavourable ambient conditions and/or time or extreme loads, including progressive degradation of material properties. This is the case for glass structures, where mostly slender load-bearing elements (with high span-to-thickness ratio) are used in combination with complementary materials (i.e., for bonding) that are often characterized by time/temperature/ambient-dependent behaviour. The relatively high span-to-thickness ratio generally manifests itself in structural masses that can be small, compared to the occupants. Human-Structure Interaction (HSI) phenomena, in this regard, may be relevant and require dedicated studies. In this paper, the dynamic performance of an existing indoor suspension glass footbridge is taken into account and explored via Operational Modal Analysis (OMA) techniques. A wide range of loading configurations (i.e., walking scenarios) are of technical interest and thus taken into account for the case-study system. These include variations in the imposed human-induced vibrations, such as the movement features, number of occupants (combined standing/walking persons), ambient conditions, size effects and mechanical restraints. Sensitivity of measured accelerations, fundamental frequencies and damping ratios for the occupied system is then discussed.
