Ultrasonic indirect method for evaluating clear wood strength and stiffness

Abstract

Strength and stiffness assessment of timber members in-service is a crucial task in the rehabilitation of a timber structure. Unsatisfactory results given by traditional procedures applied for appraisal of in-service structural timber members are a strong motivation for research on non-destructive techniques (NDT). For assessing strength and stiffness of clear wood zones of structural members an indirect ultrasonic method is proposed, given the advantage of requiring the access to only one surface of the element. This paper presents results of a study comprising three different wood species (oak, maritime pine and european spruce) with two different cross-sections and 150kHz transducers. Different arrangements of the transducers on the same surface were tested and the results compared with the ones obtained with a direct method (transducers placed at opposite ends of the specimens). The results obtained are discussed having in mind the ones already obtained in almost clear structural timber elements as well as in small size clear wood specimens.