VAXJO, Sweden -- At Linnaeus University Min Hu, PhD has been studying timber for the future of sustainable building. The focus of this research is the stiffness of the boards, which is the governing engineering property in many structural applications.

The suggested timber models in this research enable an accurate stiffness profile along timber boards, by which an effective IP to the stiffness can be established and used for the prediction of stiffness. This research will contribute to development of timber buildings, which offers major environmental benefits and contributes to a sustainable society.

IP is a parameter that is used to predict density, stiffness and strength of timber boards. The full name is Indicating Property (IP), which is established based on non-destructively assessed board properties.

According to Linnaeus University, the research will contribute to a long-term goal: The development of a method for prediction of bending strength that is more accurate than the methods available today. This work has included laboratory investigations of local material directions, and development of models for fiber directions of the interior of boards. The work also included application of one-dimensional analytical models and three-dimensional finite element models of individual boards for the mechanical behavior, analysis of mechanical response of boards based on experiments and based on the suggested models.

The suggested models were evaluated by comparisons of calculated and experimentally determined local bending stiffness along boards, and of predicted and experimentally determined bending strength.

The Linnaeus University research has also contributed knowledge on local fiber directions close to knots, and detailed information on variation of the local bending stiffness in boards. Also, fiber angle models for fiber directions in the interior of boards have been presented. By application of the fiber angle models in the three dimensional model of the whole board, the local bending stiffness along timber boards can be determined over a very short length (l < 50 mm).

A comparison with results determined on an experimental basis show a very close similarity implying that the applied models are sufficient to capture the variation of local bending stiffness, caused by knots and fiber distortions, with very high accuracy. Furthermore, it is found that by means of IPs derived using the suggested models, bending strength can be predicted with high accuracy. For a timber sample comprising 402 boards, such IPs result in coefficient of determination as high as R-squared = 0.73. However, using IPs based on the 3D finite element model did not improve the R-squared value achieved when using the IPs based on the 1D model. 

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