Influence of Varying Material Properties on the Load-Bearing Capacity of Glued Laminated Timber

https://research.thinkwood.com/en/permalink/catalogue173
Year of Publication
2014
Topic
Mechanical Properties
Material
Glulam (Glue-Laminated Timber)
Application
Beams
Author
Fink, Gerhard
Organization
ETH Zurich
Year of Publication
2014
Country of Publication
Switzerland
Format
Thesis
Material
Glulam (Glue-Laminated Timber)
Application
Beams
Topic
Mechanical Properties
Keywords
Knot Clusters
Non-Destructive
Tensile tests
Load Carrying Capacity
Joints
Model
Language
English
Research Status
Complete
Summary
Glued laminated timber (GLT) is a structural product composed of several layers of timber boards glued together. GLT components have many advantages, such as the larger range of available component dimensions to choose from, the environmental sustainability or the e- cient ratio between weight and load-bearing capacity. Because of that, GLT beams have been established as one of the most important products in timber engineering in the last decades. As a natural grown material, timber properties exhibit higher variability, compared with other building materials. The variability is pronounced not only between dierent structural elements but also within single elements, the latter being highly related to the occurrence of knot clusters. Due to the highly inhomogeneous structure of timber, the prediction of the material properties of GLT beams is aected by large uncertainties. In the presented thesis, the in uence of varying material properties on the load-bearing capacity of GLT beams was investigated. Thus the thesis contributes to develop the quality of GLT beams, in terms of reliability and eciency. Detailed, non-destructive investigations of altogether 400 timber boards were performed. Thereby, dierent strength and stiness related indicators, such as the position and characteristic of knots, or the eigenfrequency, were assessed. Furthermore, non-destructive tensile test were performed to estimate the stiness properties of knot clusters. Out of the investigated timber boards, GLT beams having a precisely-known beam setup were fabricated. As a result, the exact position of each particular timber board (and each particular knot cluster) within the GLT beams was known. Afterwards, bending tests were performed to estimate the load-bearing capacity of these GLT beams. Thereby, the in uence of knot clusters and nger joint connections on the deformation and failure behaviour was investigated. In addition to the experimental investigations, a probabilistic approach for modelling GLT beams (referred to as GLT model ) was developed. Thereby, at rst, timber boards are simulated according to their natural growth characteristics. Afterwards, out of the simulated timber boards, virtual GLT beams are fabricated. Finally, the load-bearing behaviour of these GLT beams is estimated by using a numerical model. To assure the quality of the numerical model, it was validated with the test results. Using the GLT model, the in uence of dierent parameters, such as the position and characteristics of knots, or the quality of nger joint connections, on the load-bearing capacity of GLT beams was investigated. One further goal of this thesis was the investigation of machine-grading indicators, that are measured during the grading process. Therefore, all the investigations presented in this thesis are conducted for indicators measured in laboratory and machine-grading indicators. The same applies for the GLT model, which was also developed for both types of indicators
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