Ultrasonic inspection of glued laminated timber fabricated with defects

FHWA set up a validation test to compare the effectiveness of various nondestructive inspection techniques for detecting artificial defects in glued laminated (glulam) members. The validation test consisted of a glulam beam fabricated with artificial defects known to FHWA personnel but not originally known to the scientists performing the validation tests. Ultrasonic inspection was effective in identifying voids within the glulam beam. The glulam was inspected across the width and through the depth. The inspections from each direction were combined to accurately detect and locate artificial voids in three dimensions. Wave travel time allowed identification of some of the voids, but signal amplitude parameters, such as root-mean-square voltage and peak voltage, provided more precise location of the voids. The three-dimensional image provided valuable insight into the internal condition of the glulam. However, through-the-width inspection was able to locate voids in two dimensions along the length and depth of the glulam. For a field inspection, two-dimensional location of decay would provide sufficient information for judgments to be made on the future of the inspected specimen.