Intelligent Structural Health Monitoring of Vehicular Bridges Using Fiber Optic Sensors to Detect Acoustic Emission

The recent collapse of the I-35W Mississippi River Bridge in Minneapolis has spawned a growing interest in the development of reliable techniques for evaluating the structural integrity of civil infrastructure. Current inspection techniques tailored to vehicular bridges in particular are widely based on short-term or intermittent monitoring schedules. While these techniques have had reasonable success in assessing the structural integrity of bridges, there are unanswered questions about their effectiveness for monitoring sudden adverse structural changes that can lead to catastrophic bridge failure. Structural health monitoring (SHM) is an alternative inspection paradigm that provides the potential for long-term monitoring of integrity of large-scale structures. The goal of this work is to develop an intelligent structural health monitoring (ISHM) scheme for the long-term assessment of the damage state of in-service vehicular bridges. The presented ISHM scheme builds upon an existing SHM scheme developed at the Center for Quality Engineering and Failure Prevention (CQEFP) at Northwestern University for the evaluation of the structural integrity of safety critical infrastructures. The ISHM scheme consists of diagnostic optical fiber Bragg grating (FBG) sensors for acoustic emission monitoring, signal processing techniques for source localization of acoustic emission events, and model based prediction of structural damage using the measured sensor information. Acoustic emissions consist of dynamic elastic stress waves produced by the sudden release of mechanical energy in a material, and their generation is well correlated with the growth of cracks in a structure produced by stress corrosion or mechanical fatigue from cyclic loading. As such, acoustic emission events serve as warning signs for the initiation of the process of structural failure.