Nicolas Sauvat

Experimental and numerical aspects in diffusion process characterization in tropical species

The development of timber structures in tropical regions using local species requires characterization of mechanical properties in respect to moisture content. In this context, the estimation of moisture content distribution relies on knowledge of diffusion properties in terms of sorption hysteresis and diffusion kinetics. This paper deals with experimental protocols and numerical approaches used in the 3D orthotropic diffusion characterization for Moabi and Ozigo species.

Découplage expérimental des déformations d’éléments bois sous chargements hydrique et mécanique variables

Résumé Dans la modélisation à long terme des structures en bois, plusieurs phénomènes sont pris en compte notamment la viscoélasticité, la mécano-sorption et le retrait gonflement. Le présent papier présente un protocole expérimental de découplage pour la compréhension des phénomènes rencontrés dans l’évolution de la flèche des poutres en bois soumises à des charges de longue durée. Pour cela, des essais de flexion quatre points ont été conduits en ambiance contrôlée sur des éprouvettes de petites dimensions dont nous mesurons la déflexion des faces supérieures et inférieures. L’analyse des résultats obtenus sur six mois en face supérieure et inférieure permet de découpler les phénomènes observés à savoir le retrait-gonflement transversal, l’effet verrou, la mécano-sorption orthotrope et la viscoélasticité. In long term modeling of mechanical behavior of timber elements, several phenomena have to be considered: mechano-sorption, viscoelasticity and shrinkage - swelling process are the major ones. This paper deals with an experimental procedure which separates and illustrates different phenomena observed on creep evolution of timber beams. For that purpose, a longitudinal four-point creep bending test was performed in controlled atmosphere on small samples by measuring upper and lower deflections. During six months, the result analysis allows a separation of swelling-shrinkage effect, hygro-lock effect, orthotropic mechano-sorption and viscoelasticity.

Diagnostic et comportement des ponts à ossature bois: Application au pont de Merle

ABSTRACT This paper deals with the behavior study of the timber bridge of Merle. This complex structure necessitates understanding its mechanical schema in order to predict the long-term behavior by taking into account the variable climate environment and validating the design hypotheses. Different usual displacement measures like LVDT sensors enable us to characterize displacements for singular points (beam deflections principally). In this context, a new image analysis method has been used. It allows us to obtain the displacement field of the whole bridge with a very high accuracy. In order to validate the design model, we present a 2D and 3D numeric modeling, employing the finite element method, in order to define boundaries, kinematic conditions and the global static mechanical properties by operating an inverse analysis method.

Couplage hygromécanique dans le processus de diffusion dans le bois

ABSTRACT Mechanical properties of timber constructions depend strongly on moisture content state. In this context, it is shown a mecanosorptive coupling. This climatic environment aspect imposes a hygroscopic behavior modeling in order to estimate moisture content variations by integrating the heat and mass transfer processes. If the effect of moisture content on the mechanical behavior has been studied in the literature, this work enables us to precise effects of mechanical state on the transfer laws by taking into account boundary conditions and diffusion properties. In this context, we propose a thermodynamic and experimental approaches which allow to introduce a realistic coupled transfer algorithm in a finite element software.

Using the chemical mass balance model to estimate VOC source contributions in newly built timber frame houses: a case study

Basing on the material emission data obtained in a test chamber, chemical mass balance (CMB) was used to assess the source apportionment of volatile organic compound (VOC) concentrations in three newly built timber frame houses. CMB has been proven to be able to discriminate the source contributions for two contrasted environmental conditions (with and without ventilation). The shutdown of the ventilation system caused an increase in the VOC concentrations due to the increased contribution of indoor surface materials like the door material and furniture explaining together over 65% of total VOCs. While the increase in formaldehyde concentration is mainly due to furniture (contribution of 70%), the increase in α-pinene concentration is almost exclusively attributable to the emission of door material (up to 84%). The apportionment of VOC source contributions appears as highly dependent on the position of source materials in the building (surface materials or internal materials) and the ventilation conditions explaining that the concentrations of compounds after the shutdown of ventilation system do not increase in equivalent proportion. Knowledge of indoor sources and its contributions in real conditions may help in the selection of materials and in the improvement of construction operations to reduce the indoor air pollution.