This paper describes a preliminary study on the use of ultrasonic Lamb waves for detecting fatigue cracks and other types of defects in steel girders at long distances. Lamb waves are capable of propagating long distances, making them ideal for detecting defects in large portions of bridge girders with the transducer placed at an easily accessible location. In this study, practical field testing methods and procedures for detecting fatigue cracks were developed in the laboratory by testing small steel members and a large W section. These methods were then used in a field test of a steel girder biridge to determine if fatigue cracks could be detected in the area of a connection to the web at long ranges. Results from the laboratory tests indicate that cracks can be detected at long ranges using Lamb waves. Field test results indicated that Lamb waves can be used to detect fatigue cracks in the area of a connection to the girder web.
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