The Hygroscopic Warping of Cross-Laminated Timber

Author

• Thomas GerekeEmail author
• Per Johan Gustafsson
• Kent Persson
• Peter Niemz

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3. 3.

Chapter

First Online: 

20 October 2010

Abstract

This chapter focuses on moisture-induced deformations in three-layered cross-laminated timber with a symmetrical build-up, where the fibre direction of the middle layer is oriented perpendicular to that of the outer layers. Dimensional stability, i.e. the ability to resist warping, is of main interest for the application of such wood panels. The cross lamination of the layers is advantageous to warping. The moisture-induced expansion/contraction of each single layer is partly restrained by the adjacent layers. The free swelling and shrinkage of adjacent layers differ approximately by a factor of 10 (radial/longitudinal) to 20 (tangential/longitudinal). As a consequence of this difference, stresses and even cracks may occur. In large-scale panels warping was observed. This reduces the serviceability in the practice. Due to a climate gradient considerable distortions (warp) in the form of cup and twist may occur. Models to calculate the moisture and stress fields are provided and validated to experimental tests.

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