Steel bridges are susceptible to a variety of deterioration conditions including fatigue damages resulting from the irregular loadings of various traffic volumes. Fatigue is best defined as the initiation and propagation of microscopic cracks into macro cracks by the repeated application of stresses. To evaluate damage, the Federal Highway Administration (FHWA) uses condition ratings in bridges as a way to classify a structure’s current condition and inherent durability. However, the quality of the condition-ratings is subjective (visual inspection based on the inspectors view) and time delayed due to inspection cycles, which are scheduled for every two years. Furthermore, fatigue damage can slip from visual inspections due to the lack of visible signs and can even fracture before showing visible signs of damage. Through structural health monitoring technologies and non-destructive evaluation techniques, implementing sensors on bridges can act as effective monitoring systems to detect damage, including sensing of small cracks developing in fatigued members. Further, the implementation of SHM and NDE technologies can be grouped with engineering analyses to provide inspectors with an accurate quantification of a structure’s damage and the service life of infrastructure. These modern technologies can specifically be applied to steel bridges as part of an Integrated Structural Health Monitoring (ISHM) system, particularly suited for the fatigue detection of highway steel bridges.
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