Integrity monitoring of fracture critical bridges

Many bridges worldwide are approaching the end of their lifespan and it is necessary to assess their health condition in order to mitigate risks, prevent disasters, and plan maintenance activities in an optimized manner. The fracture critical bridges are of particular interest since they have only little or no load path redundancy. Structural health monitoring (SHM) recently emerged as a branch of engineering with a great potential to help the assessment of structural condition. Distributed optical fibre sensing technology has opened a new possibility in structural health monitoring. Distributed deformation sensor (sensing cable) is sensitive at each point of its length to strain changes and cracks. Such a sensor practically monitors one-dimensional strain field and can be installed over all the length of monitored structural members (suspension cables, girders, etc.), and therefore provide for integrity monitoring, i.e. for direct detection and characterisation (including recognition, localization, and quantification or rating) of local strain changes generated by damage. Integrity monitoring principle for bridges is developed and presented in this paper. Finally, a large scale real on-site application is briefly presented.