Experimental study on glued laminated timber beams with well-known knot morphology

Abstract

Nowadays, the impact of knots on the failure behaviour of glued laminated timber (GLT) beams is considered by subjecting the single lamellas to a strength grading process, where, i.a., tracheid effect-based laser scanning is used to obtain information about knot properties. This approach single-handedly defines the beam's final strength properties according to current standards. At the same time, advanced production processes of such beams would allow an easy tracking of a scanned board's location, but, at this point, previously obtained detailed information is already disregarded. Therefore, the scanning data is used to virtually reconstruct knot geometries and group them into sections within GLT beams. For this study, a sample of 50 GLT beams of five different configuration types was produced and tested under static four-point-bending until failure. As for each assembled lamella the orientation and position within the corresponding GLT beam is known, several parameters derived from the reconstructed knots can be correlated to effective GLT properties. Furthermore, the crack patterns of the tested beams are manually recorded and used to obtain measures of cracks. A detailed analysis of the generated data and their statistical evaluation show that, in the future, dedicated mechanical models for such timber elements must be developed to realistically predict their strength properties. A potential approach, using fluctuating section-wise effective material properties, is proposed.

Calibration and Validation of a Linear-Elastic Numerical Model for Timber Step Joints Based on the Results of Experimental Investigations

“…Various experimental tests of timber joints show a strong dependence of the results on the inhomogeneous material properties of the sample, in particular the arrangement and twist of the fibres, as well as the presence of knots [ 9 , 10 ]. Furthermore, the results are dependent on the chosen geometry of the joint and the accuracy of craftsmanship in regard to the execution [ 7 ].…”

Predicted and Experimental Bending Behaviour of Glulam Bonded by RPF Adhesive

“…Material, here wood, was modelled as an elastic material without considering the failure. Additionally, the model does not consider any wood defects, although there are already studies dealing with this issue [2]. In order to model the elastic region, it is necessary to know several basic material characteristics.…”

“…It is a sustainable option because it is made from a renewable resource and has a smaller carbon footprint compared to these other materials [1]. Another great advantage of glulam is that lamellae with better mechanical properties are used for production; therefore, by selecting and combining such lamellae, it is possible to obtain higher values of characteristic strengths than can be achieved with solid wood [2].…”

Bending test on large-scale GLT beams with well-known beam setup using machine grading indicator

“…Foschi and Barrett 1980; Colling 1990; Blaß et al 2009; Fink et al 2015; Kandler et al 2018) Some of the experimental studies have been performed on GLT beams with known beam setup; e.g. Ehlbeck and Colling (1987a, 1987b) recorded the position of the timber boards and knots of the lowest 2 lamellas, Fink et al (2015) and Kandler et al (2018) recorded the entire beam setup based on machine grading information. Nevertheless, so far none of these tests have been performed on large-scale tests, which are needed for the validation of GLT models.…”