Advancing Structural Health Monitoring: Case Studies in Operational Modal Analysis for Existing Structures

Aging infrastructure has become a pressing concern nowadays, particularly in countries like Italy where major infrastructures were built more than 60 years ago. Structural health analyses and investigations on these existing structures should be performed without damages or service interruptions. Modal analysis, aimed at identifying eigenfrequencies and eigenmodes, proves to be a highly effective strategy for understanding structural characteristics. In this work we present two compelling cases of Operational Modal Analysis OMA. The first case focuses on a 154-m-long viaduct constructed using a system of pre-stressed reinforced concrete box girders, divided into five spans of almost 30 m each. The second case involves two reinforced concrete ‘arch-stayed’ type bridges with a span of 55.25 m. In both instances, experimental OMA has been conducted to identify structural eigenfrequencies, which have been used to evaluate the structural mechanical characteristics. This approach addresses an inverse problem, where the results of experimental modal analyses are considered as known inputs, while the structural parameters of a mathematical model representing the real structure are the unknowns. This method can help the identification of constraint conditions, material characteristics, and, in general, serves as an effective approach for structural health monitoring of bridge structures.