Abstract Glued laminated timber (glulam) is known in timber constructions since more than 100 years. Glulam members can delaminate due to aging and excessive changes of temperature and humidity. This results in significantly reduced load bearing capability of the affected structural members. This contribution focuses on the ultrasonic point-contact inspection of gluing plane delamination as a nondestructive method. Ultrasonic measurements on a section of a 90-year-old roofing glulam member are presented. The results are compared with manual detection and evaluation of delamination with a feeler gauge, with X-ray computed tomography analyses, and with numerical simulations. Appropriate data evaluation of the mechanized ultrasonic results allows the determination of material separation that are deeper than 20 mm in the signature of the surface wave and large-scale delamination (>80% of the complete bonding width) in the back-wall echo. Numerical simulations based on the finite-difference time-domain method shed light into the details of the wave propagation and support the experimental findings.

Timber bridges have been built for decades all around the world. The hygroscopic material behavior of wood leads to the change of the moisture content of the wood and the dimensions depending on the climate. Therefore in regular inspections following questions arise: what happens with the wood due to the climate changes? Are there major changes of the moisture content? Are there differences between the natural material axes or within the cross section of the structural members? To answer these questions, traffic timber bridges with big cross sections are long term monitored within a research project. The results of the moisture contents measured and a comparison between the different measuring groups and positions are presented. The analyses confirm that the moisture content in the wood follows the climate changes delayed and with smaller amplitude against the calculated equilibrium moisture content. In first steps, a different behavior of the change of the moisture content could be determined over the cross section and along the span of the member.

The applications and limitations of different non-destructive and semi-destructive techniques to evaluate the structural integrity of timber members in a pedestrian bridge are presented as a case study. Sophisticated assessment tools are required to detect hidden damages in timber structures: for example stress-wave techniques are used to evaluate the modulus of elasticity of bending members and resistance to drilling is used to gain knowledge of areas of changed density due to insect or moisture induced damages. Reliably relating the gathered data to the structural integrity of the structure is a complex issue. Bending members and connection details of a decommissioned timber bridge were evaluated using non destructive assessment tools. Eventually these parts were tested destructively to assess their remaining modulus of elasticity and load bearing capacity. The need for improvements in the current practice is highlighted by comparing the results from the non-destructive, semidestructive and destructive tests. Résumé Les applications et les limites de différentes techniques d’analyse non destructives de structures porteuses en bois sont présentées dans le cas concret d’une passerelle piétonne. Des moyens d’investigations sophistiqués ont été mis en œuvre pour déceler des dommages cachés : par exemple, les ultrasons sont couramment utilisés pour mesurer le module de Young d’éléments porteurs et la résistance à la pénétration est souvent utilisée pour déterminer l’étendue des attaques d’insectes ou de pourritures suite à des champignons lignivores qui provoquent de fortes chutes de la densité du bois. Des éléments porteurs et des assemblages d’un pont piétonnier désaffecté ont été évalués par des moyens non destructifs. Par la suite, ces éléments et assemblages ont été testés de manière classique afin d’en déterminer la capacité portante et le module de Young résiduel. Les besoins d’amélioration des pratiques actuelles sont démontrés par la comparaison des résultats des mesures non destructives avec les mesures classiques destructives.