, Volume 9, Issue 3, pp 189-205

The viscoelasticity of wood at varying moisture content

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Abstract

Wood is regarded as a viscoelastic material. Creep deformations that arise from variations in the moisture content are described by a theory of hydroviscoelasticity developed by the author. Two different types of behaviour have been apparent: one, arising from a continuously increasing strain with periodic variation in the moisture content, and another with no cumulative effect. The theory has been applied to previously published experimental results concerned with beech, pine, hoop pine, klinki pine, along with birch and spruce plywood. Birch and spruce plywood have been used for experiments concerned with periodically-cycling bending moment and moisture content. The results obtained have been compared with the theory presented. Glue-laminated beams have been subjected to long-term outdoor loading extending for five years. A brief discussion is given of the results obtained.

The author is indebted to Professor Siimes and Mr. Saarelainen for the planning and carrying out of glue-laminated beam tests and for being kind enough to make the results available to the author for publication. The author acknowledges the valuable assistance of Mr. Kortesmaa in connection with recovery experiments, and computation of the results.