Moisture-induced stresses in large glulam beams. Case study: Vihantasalmi Bridge

Abstract

The structural performance of timber elements may depend on the environmental conditions and in particular on the cyclic variations of the moisture content. Moisture gradients in the sections of the structural elements can produce additional stresses, the so-called moisture-induced stresses (MIS), which can cause the formation of cracks and delamination in wooden components. In order to achieve a reliable evaluation of the safety level of timber structures, the present paper proposes a numerical methodology to evaluate the MIS in glulam beams of timber bridges under Northern European climates and mechanical loads. A hygro-thermal multi-Fickian model for prediction of moisture content, relative humidity and temperature in wood is sequentially coupled with an orthotropic-viscoelastic-mechanosorptive model for calculation of wood stresses. Both models were developed by some of the authors in Abaqus FEM code in previous works and their coupling is used here to analyse the hygro-thermo-mechanical response of a glulam beam of Vihantasalmi Bridge in Finland under bending loads. Both perpendicular and parallel to grain MIS in a beam section sheltered from rain are evaluated during a 10-year analysis and conclusions on the crack risk related to these stresses are given.

Normal stress distribution of timber-concrete composite panels with an adhesive shear connection under thermal and humidity loadings

“…The moisture content varies in time and over the cross-section according to the diffusion laws (Toratti 1992;Fortino et al 2019) and the process depends on the diffusion coefficient, surface emissivity of timber, and moisture content flux through the boundary of the timber cross-section. The temperature and humidity distribution in the TCC crosssection is not uniform after a change in temperature and relative humidity of the environment.…”

“…Timber, concrete, and adhesive have different hygrothermal properties; in addition, timber has different mechanical and hygrothermal properties in various directions, being an orthotropic material (Rindler et al 2017;Chiniforush et al 2019). The changing temperature and moisture cause internal stresses when components are bonded together (Bagoňa et al 2011;Ginz and Seim 2018;Fortino et al 2019;Fojtík et al 2020). The uneven thermal and humidity deformations of each layer of the TCC can lead to the local failure of the timber or concrete part or the delamination of the composite panel (Song et al 2021).…”

A three-dimensional numerical analysis of moisture flow in wood and of the wood’s hygro-mechanical and visco-elastic behaviour

“…Many studies regarding the impact of moisture gradients on beam bending in which simulations have been involved have been carried out. These have concerned both controlled changes in climate (Honfi et al 2014;Ranta-Maunus 2001) and changes in climate that occur naturally (Fortino et al 2019b;Franke et al 2019;Müller et al 2007;Toratti 1992). A variety of constitutive models has been used in such studies, involving one-, two-or three-dimensional space considerations.…”

Health Monitoring of Stress-Laminated Timber Bridges Assisted by a Hygro-Thermal Model for Wood Material

“…As shown in the recent literature [10][11][12], advanced multi-phase models are an effective tool to assist the hygro-thermal monitoring of timber bridge components such as glulam beams. Compared to the single-phase (or single-Fickian) models for transient moisture transport in wood [13][14][15], where the MC is the only variable of a Fick's second law equation, the multi-phase models below the fibre saturation point (FSP) analyse two different water phases, i.e., the water vapour in lumens and the bound water in wood-cell walls.…”

“…The multi-Fickian theory below the FSP is based on the identification of three phenomena occurring in cellular wood during moisture transfer, i.e., the diffusion of water vapour in the lumens, the sorption of bound water and the diffusion of bound water in the cell walls. In the multi-phase models available in the current literature, the two water phases are separated and the coupling between them is defined through a sorption rate [10][11][12][17][18][19][20]. Recently, Autengruber et al [21], developed a whole multi-Fickian model including also the transport of free water in the lumens above the FSP.…”