In-situ assessment of timber structural members: Combining information from visual strength grading and NDT/SDT methods - A review

The non-destructive assessment of mechanical properties of timber members in situ is currently done by applying visual strength grading standards (VSG) which were developed specifically for sawn timber. The well-known limitations of the full application of VSG in situ lead to the necessity to adapt those standards. This was done by selecting the most important strength-reduction features and considering insight information such as the position of defects with regard to stress distribution in the element. Concurrently, to tackle the subjectivity and limitations of VSG, other non- and also semi-destructive testing (NDT/SDT) methods were developed to support/validate the VSG results. This paper presents a review of the application of VSG in situ and the way the information has been combined with information provided by other NDT/SDT methods to obtain a more reliable assessment of the mechanical performance of timber structural members.