Combination of non-destructive tests for assessing decay in existing timber elements

Existing timber structures often present elements with different levels of decay and the choice to maintain them comes from the structural assessment, made by a civil engineer on the basis of the results coming from the on-site survey. The choice may also rely on visual inspection combined non-destructive tests. In that case, the choice to maintain an element will greatly depend on the accuracy and reliability of the results obtained through these tests. This work aims to assess the properties of timber elements through non-destructive tests, using resistance drilling, pin penetration, ultrasound, and acoustic emission tests. The tests were carried out on three timber elements from two old timber roof trusses. The results are analysed regarding the specimen size and the use of multiple non-destructive test parameters. Decay was initially identified by means of visual inspection and different levels of decay were identified taking into account their influence on the non-destructive test results and on the predictability of models based on single and multiple regression analysis. Moreover, the obtained classification was found to increase the reliability on the prediction of density.