Diagnostic analysis and dynamic identification of a glass suspension footbridge via on-site vibration experiments and FE numerical modelling

Structural glass represents a relatively new solution for constructions, requiring appropriate knowledge, but is largely used for facades, roofs, footbridges, etc. There, composite systems in which multiple glass members can interact with traditional building materials, should offer appropriate fail-safe performances, within the full lifetime. Further efforts are needed for the vulnerability assessment of glazing systems under extreme loads (seismic events, fire, etc.) or severe operational conditions. In this paper, the dynamic characterisation of an existing glass suspension footbridge is presented for a case study structure in Italy. On-site vibration experiments are first discussed, based on Operational Modal Analysis (OMA) techniques, so as to estimate the fundamental parameters of the composite glass footbridge. A Finite Element (FE) numerical study is then carried out, to further assess and explore the structure performance, including a sensitivity investigation. It is shown how the key dynamic parameters can be susceptible to even minor variations of few geometrical/mechanical influencing parameters, or to possible localised damage scenarios, hence affecting the overall composite behaviour of the glazed structure and requiring careful consideration for design and maintenance purposes. Degradation phenomena in the bonding layers, in particular, can severely affect the overall structural estimates and performances. While existing analytical models can provide simplified estimations only, in addition, the actual restraint configuration of all the assembly components should be also properly taken into account for reliable predictions.