Non-destructive diagnostics for timber structures in historic buildings : Investigation methods and testing tools

Abstract

ABSTRACT: Non-destructive testing is a relatively new field in construction and shows great potential for in-situ testing. Especially for historic structures where no alterations, interventions or damages due to tests are desirable, this form of assessment is ideal. Problematic is that only very little regulations in form of standards and codes exist in this field that would harmonize not only the assessment procedure but also the procedure of the individual techniques. This report performed a theoretical research study to investigate the different techniques and evaluate their potential, limitations as well as their practical implementation so far. The reviewed techniques include visual inspection, moisture measurement, ultrasonic measurements, radioscopy, thermography, ground penetrating radar and the semi-destructive Resistograph (resistance drilling). Following the theoretical part of the study, available codes, standards and guidelines concerning this field of work were critically analyzed. Among these standards were the Euro Code 5, ISO 13822, SIA 269 and UNI 11119. The Italian standard UNI 11119 was thereby the only one available in detail and used for the development of a guideline/best practice consisting of non-destructive techniques that would satisfy the requirements set by the standard. It was concluded that the separate techniques are best used in combination as one alone is not sufficient enough to fulfil the standard’s requirements. A laboratory investigation using some of the reviewed techniques was performed as well, confirming the benefits of combining techniques as salience form visual inspection was confirmed by resistance drilling and ultrasonic through-transmission for instance. The resulting laboratory report can be found in the annex. A conclusion was drawn that the benefits of non-destructive assessments are plentiful as it allows investigating structures without disturbing them, using non-destructive techniques in situ. This is crucial for historical structures as it is possible to differentiate between sound and damaged structural members, which decreases the amount of interventions significantly, preserving cultural heritage.