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Moisture-induced stresses perpendicular to grain in cross-sections of timber members exposed to different climates

Fragiacomo, Massimo and Fortino, Stefania and Tononi, Davide and Usardi, Irene and Toratti, Tomi (2011) Moisture-induced stresses perpendicular to grain in cross-sections of timber members exposed to different climates. Engineering Structures, Vol. 33 (11), p. 3071-3078. ISSN 0141-0296. eISSN 1873-7323. Article.

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DOI: 10.1016/j.engstruct.2011.06.018

Abstract

In variable humidity conditions, wood absorbs or desorbs moisture from the air. Unless the change in humidity is very slow, this will develop moisture gradients in the wood sections. These gradients will develop stresses due to constrained swelling or shrinkage strains. These stresses are named moisture-induced stresses. The present paper investigates the main parameters affecting such moisture-induced stresses, including the type of climate, the size of the timber cross-section, and the type of protective coating. A first attempt to identify moisture-induced stresses in different European climatic regions was made. For each climatic region, relative humidity and temperature histories were identified, and characteristic and mean values of yearly and daily variations were calculated. Using a finite element model implemented in Abaqus, the moisture content and stress distribution were computed on different timber cross-sections exposed to the climatic regions and protected with different types of coating. A Fickian moisture transfer model was used to compute the moisture distribution, and a mechanical model for time-dependent behaviour of wood was implemented to calculate the corresponding stress distribution. The variation of moisture was found to result in stresses of magnitudes that would probably cause cracking of wood in the perimeter of any uncoated cross-section size. The use of a protective coating, however, reduced considerably the moisture-induced stresses, and can be regarded as an effective protective measure to avoid cracking due to humidity variations. Considering European climates, Northern climates were found to result in higher surface tensile stresses than Southern climates.

Item Type:Article
ID Code:6385
Status:Published
Refereed:Yes
Uncontrolled Keywords:Abaqus code, climatic zones, finite element analyses, moisture-induced stresses, timber structures
Subjects:Area 08 - Ingegneria civile e Architettura > ICAR/09 Tecnica delle costruzioni
Area 08 - Ingegneria civile e Architettura > ICAR/09 Tecnica delle costruzioni
Divisions:001 Università di Sassari > 01 Dipartimenti > Architettura e pianificazione
Publisher:Pergamon / Elsevier
ISSN:0141-0296
eISSN:1873-7323
Copyright Holders:© 2011 Elsevier Ltd.
Deposited On:23 Aug 2011 13:40

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