Abstract
An orthotropic steel deck is a type of slab that has the function of directly supporting trucks on bridges. Since orthotropic steel decks are constructed by welding together thin steel plates, numerous fatigue cracks have occurred on routes with heavy truck traffic. In particular, cracking at the rib-to-deck welds in orthotropic steel decks poses one of the most serious problems. Cracks in the rib-to-deck welds cannot be detected by visual inspection and can be investigated most effectively by ultrasonic testing. The main issues with conventional manual testing are that it takes a lot of time to detect the cracks and that skilled engineers are required. This paper introduces a newly developed cutting-edge ultrasonic imaging method and its application to inspect deck plate fatigue cracks and bead fatigue crack of orthotropic steel deck bridges. The inspection system presented here involves advanced high-speed ultrasonic inspection equipment that incorporates parallel processing circuitry for image synthesis and a remotely operated four-wheel scanner with an ultrasonic array probe for angle beam inspection. The system is capable of synthesizing 3D images of the crack propagation and its shape with high resolution along the weld line, in real time, by integrating the B-scope images taken after each 2 mm of scanner movement. Through verification testing of fatigue crack propagation test specimens, it was confirmed that this inspection system gives improvements of inspection performance by achieving better crack shape visualization and a higher measurement accuracy of ±0.8 mm at a depth of 1.3 mm or more for a deck plate crack and ±1.0 mm at a depth of 1.9 mm or more for a bead crack compared to traditional inspection methods. Verification tests are currently being conducted on actual bridges, with a practical application planned for the near future.
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