Overview of 40 bridge monitoring projects using fiber optic sensors

In the last 15 years, fiber optic sensing has become a useful and increasingly widely used tool for structural health monitoring of bridges and other civil structures. We have been fortunate to participate to their development and introduction to real field applications. This paper is an overview of 40 bridge monitoring projects carried out over the last 15 years in 13 different countries. In particular we concentrate on the analysis of the different types of bridges that were monitored, their situation (new construction, existing structure, refurbishment.) and the main purpose of the installed monitoring system. Two main categories emerge form this analysis: new bridges with innovative aspects or particular relevance and existing bridges with known deficiencies. We will than analyze the most typical sensor architectures used to monitor those bridges, giving statistics on the number and type of installed sensors, their survival rate and the duration of the monitoring project. For some projects, the monitoring concentrated on a specific event in the life of the bridge, for example its construction or refurbishment. Other projects aimed to longterm monitoring and are still running, in some cases after almost 10 years. In the early applications of fiber optic technology the cost of the measurement instruments and their fragility were discouraging permanent monitoring and many projects called for periodic manual measurements. In the last 5 years, significant progresses in the instrument reliability and lower cost have enabled a growing number of permanent instrumentations. Another interesting aspect concerns the entities involved in each monitoring project. We will analyze weather the project originated form a research entity (university, research institute) or was driven more by the bridge owners. Finally we will summarize the main findings of each project and show concrete examples of actionable information that could be gained thanks to monitoring.