Output-Only Modal Analysis and System Identification for Indirect Bridge Health Monitoring: Needs, Requirements, and Limitations

Vibration-Based Structural Health Monitoring (SHM) relies on analyzing the vibrational response of structures to identify damagesensitive features, offering early warnings of potential structural anomalies. Widely adopted over the past decades, these methods typically utilize data from permanently installed sensing devices, enabling continuous and permanent dynamic monitoring under ambient excitation. Operational Modal Analysis (OMA) algorithms play a crucial role in extracting damage-sensitive modal parameters, such as natural frequencies and associated mode shapes. Despite the success of this traditional framework, challenges arise when applied to extensive road networks, such as the Italian highway system, characterized by a multitude of bridges and viaducts spanning over 3,000 km. Consequently, there has been a notable surge in interest in recent years in drive-by or indirect Bridge SHM (iBSHM), where data is collected by a moving sensing vehicle. However, characterizing bridge dynamics solely based on output recorded during vehicle movement or while stationary presents a complex undertaking. This paper aims to provide a comprehensive overview of the primary theoretical and practical challenges in the realm of drive-by or indirect SHM. Additionally, it explores the necessary enabling technologies to effectively address these challenges, shedding light on the evolving landscape of structural health monitoring in extensive infrastructure networks.