Paper of the Month November: Infrastructure Distributed fibre optic acoustic sensing for bridge monitoring

01/11/2022

Bridges are essential for modern transport infrastructures and their condition is of immense importance for our society. Systematic condition monitoring of bridge infrastructures for the purpose of early detection and location of damages is therefore mandatory to prevent catastrophic events. Distributed vibration measurement using distributed fibre optic acoustic sensors is an efficient method for bridge monitoring.

The Division "Fibre Optic Sensors" at BAM has been involved in the development of distributed fibre optic acoustic sensors for bridge monitoring, for years. The sensor technique is based on the distributed, high-sensitive measurement of the intensity and phase of the backscattered light in the fibre, which are influenced by acoustic vibrations in the environment. This way, the optical fibre is transformed into a series of microphones, making it possible to detect vibrations along the bridge, seamlessly. The obtained sensor signals provide information about the location, the frequency and the amplitude of the vibrations.

A new fibre optic acoustic sensor technique developed at BAM (the intensity-based coherent optical time domain reflectometry) was recently used to measure vibrations of a decommissioned bridge in Brandenburg, Germany. By intentionally destructing the bridge, various bridge damages (such as cracks) were induced. The vibration signals obtained with the innovative fibre optic sensor system during the destruction process provided important information that helped civil engineers to evaluate the condition of the bridge and to detect and localize existing damages.

Application of Intensity-Based Coherent Optical Time Domain Reflectometry to Bridge Monitoring
Xin Lu, Sebastian Chruscicki, Marcus Schukar, Sven Münzenberger, Katerina Krebber
published in Sensors, Vol. 22, issue 9, page 3434, 2022
BAM Fibre Optic Sensors division