Static and dynamic bridge monitoring with distributed fiber optic sensing

Structural health monitoring (SHM) of bridges and other critical infrastructure is progressively gaining more importance, especially since many bridges in Central Europe and North America are coming to the end of their design life time. Efficient monitoring is therefore necessary to ensure safe operation. In order to measure not only fast changes due to traffic loads but also slow changes caused by temperature or degradation, several different sensor types are usually needed. Distributed Fiber Optic Sensing (DFOS) can provide both static and dynamic information. This article focuses on the monitoring of a steel-concrete composite highway bridge in Austria. Two of the seven spans were equipped with fiber optic sensing cables. By using different DFOS techniques such as Distributed Acoustic Sensing (DAS) and Brillouin Optical Frequency Domain Analysis (BOFDA), both dynamic and static monitoring can be realized seamlessly along the sensing cables. The combination of both fiber optic measurement techniques allows the determination of the vibration behavior of the bridge where not only the eigenfrequencies can be observed, but also slow changes caused by external influences such as temperature. We demonstrate that individual vehicles can not only be identified in DAS measurements, but also characterized in terms of mass and speed. To verify the static and dynamic DFOS results, point-wise sensors such as Robotic Total Stations (RTS) and accelerometers are used as reference.