Comparison between Predicted and Measured Moisture Content and Climate in 12 Monitored Timber Structures in Switzerland

Wood is a hygroscopic material that primarily adapts its moisture content to the surrounding relative humidity. The climate in a structure or building depends on the building type and the region the structure is located in. In this study, the effect of region on the moisture content of wood was investigated. Measurements taken in 12 ventilated timber structures were compared to the theoretical equilibrium moisture content calculated from the relative humidity and temperature in 107 meteorological stations across Switzerland. The monitored load-bearing elements were made of softwood and protected from the direct impact of weather. The climatic conditions around the Alps, a mountain range that runs from France to Austria and crosses Switzerland, can be divided into the following three different regions: (1) south of the Alps, where the climate is affected mainly by the Mediterranean sea; (2) north of the Alps, where the climate is affected by the Atlantic Ocean; and (3) the inner Alps, where the climate is considered to be relatively dry. The climatic conditions of the three separate regions were reflected in the measurements made in the monitored timber structures. Differences between the regions were quantified. The moisture content and relative humidity, similarly to temperature, depended on altitude (above sea level).

Moisture buffering effect of hygroscopic materials under wall moisture transfer

Hygroscopic material can moderate the indoor humidity variation due to its moisture buffering effect. This effect would change when used as interior finish mainly due to air exchange and wall moisture transfer. The author focused on clarifying the extent of the wall'’s influence on indoor moisture buffering and building humidity environment. A room model was established and the situation of no wall moisture transfer was simulated by adding a vapour barrier between the interior finish and the wall. Comparing this result with wall moisture transfer, the moisture buffering effect of the wall can be quantitatively analysed. The results verify that the buffering effect and the humidity environment, especially the seasonal buffering, change with the wall moisture transfer. The wall has great impacts on buffering in the cases of thin interior finish, high moisture production and low ventilation. Because the layer under the hygroscopic material also has buffering capacity, the difference of using various thicknesses of material is not obvious. Frequent ventilation reduces the buffering effect but improves the RH optimality.

Formalizing shape-change: Three-dimensional printed shapes and hygroscopic material transformations

Shape-changing materials have become increasingly popular among architects in designing responsive systems. One of the greatest challenges of designing with these materials is their dynamic nature, which requires architects to design with the fourth dimension, time. This article presents a study that formalizes the shape-changing behavior of three-dimensional printed wood-based composite materials and the rules that serve to compute their shape-change in response to variations in relative humidity. In this research, we first developed custom three-dimensional printing protocols and analyzed the effects of three-dimensional printing parameters on shape-change. We thereafter three-dimensional printed kirigami geometries to amplify hygroscopic material transformation of wood-based composites.

Influence of hydric solicitations on the morphological behavior of hemp concrete

The use of bio-based materials such as hemp concrete in the field of construction allows limiting environmental impacts and improving the energy performances of buildings. The aim of this paper is to understand the influence of adsorption and desorption of moisture in hemp concrete on its internal morphology and its dimensional variations. That’s why, the high porosity and the adsorption capacity of hemp concrete were discussed. Then, an experimental cell was developed to follow the geometric evolution over time of hemp concrete microstructure under hydric solicitations: humidification and drying. The digital image correlation was used to determine the strains fields on the surface of the material. This technique showed the behavior of this hygroscopic material subjected to different hygrometries. Indeed, the hemp shiv undergoes larger strains than the binder, thus affecting the morphology of hemp concrete. The results obtained highlighted the influence of the hydric state of hemp concrete on its very heterogeneous microstructure. It has also been revealed that the durability of the material can be affected by the dimensional variations caused by the relative humidity variations.

DETERMINATION OF HYGROEXPANSION COEFFICIENTS OF WOOD USING ANALYTICAL AND NUMERICAL HOMOGENIZATION

This paper is concerned with the determination of hygroexpansion coefficients of wood. Wood is a naturally hygroscopic material, attracting moisture from its surroundings. Its dimensions change depending on the actual moisture content. This dependence is characterized by the coefficient of hygroexpansion. For complex microstructures, this coefficient can be determined, similarly to the coefficient of thermal expansion, either from analytical or numerical homogenization. The homogenization procedure, used in this paper, comprises several steps corresponding to the wood structural composition. Accuracy of this approach is governed by correctness of the chosen input parameters. One of the most important parameters are the volume fractions of the earlywood and latewood. Ascertained dependence of the earlywood and latewood volume fractions on dry wood density is also presented.