Sensor array for the health monitoring of truss structures by means of guided ultrasonic waves

This paper presents the results of an experimental work where guided ultrasonic waves (GUWs) were used for the health monitoring of a real size truss, which was part of a highway variable message sign structure dismantled from service. The monitoring strategy proposed here combines the advantages of GUWs with the extraction of defect-sensitive features to perform a multivariate diagnosis of damage. The effectiveness of the proposed approach is tested by monitoring the propagation of waves along one of the main chords of the truss and by observing the onset and growth of two artificial cracks. The ability to diagnose the presence of these artificial defects located around the welded joints between one main chord and two diagonal members concurring on the weld is discussed. It is shown that by exploiting the stepwise response of the Mahalanobis squared distance, it is possible to discriminate and quantify defects of various sizes; moreover, it is found that certain wave paths better identify the position of damage.