Recent research in the field of assessment of hygrothermal response has focused on either laboratory experimentation or modelling, but less work has been reported in which both aspects are combined. Such type of studies can potentially offer useful information regarding the benchmarking of models and related methods to assess hygrothermal performance of wall assemblies.
This report documents the experimental results of a benchmark experiment that was designed to allow benchmarking of stud drying predicted by NRC’s an advanced hygrothermal computer model called hygIRC, when subjected to nominally steady-state environmental conditions. hygIRC uses hygrothermal properties of materials derived from tests on small-scale specimens undertaken in the laboratory. The drying rates of wall assembly featuring wet studs that result from moisture accumulated during the framing stage of a 5 or 6 storey building. The drying rate of those studs was assessed in an experiment undertaken in a controlled laboratory setting. The results were subsequently used to help benchmark hygIRC reported under separate cover.
Characteristics of the Radio-Frequency/Vacuum Drying of Heavy Timbers for Post and Beam of Korean Style Housings Part II: For Korean Red Pine Heavy Timbers with 250 × 250 mm, 300 × 300 mm in Cross Section and 300 mm in Diameter, and 3,600 mm in Length
This study examined the characteristics of radio-frequency/vacuum dried Korean red pine (Pinus densoflora heavy timbers with 250 × 250 mm (S), 300 × 300 mm (L) in cross section and 300 mm in diameter, and 3,600 mm in length, which were subjected to compressive loading after a kerf pretreatment. The following results were obtained : The drying time was short and the drying rate was high in spite of the large cross section of specimens. The moisture gradient inall specimens was gentle in both longitudinal and transverse directions owing to dielectric heating. The shrinkage of the width in the direction perpendicular to was 21 percent ~ 76 percent of that of the thickness of square timbers in the direction parallel to the mechanical pressure. The casehardening for all specimens was very slight because of significantly reduced ratio of the tangential to radial shrinkage of specimens and kerfing. The surface checks somewhat severely occurred although the occurrence extent of the surface checks on the kerfed specimens was slight compared withthat on the control specimen.
Cross-Laminated Timber (CLT) is an engineered mass timber product manufactured by laminating dimension lumber in layers with alternating orientation using structural adhesives. It is intended for use under dry service conditions and is commonly used to build floors, roofs, and walls. Because prolonged wetting of wood may cause staining, mould, excessive dimensional change (sometimes enough to fail connectors), and even result in decay and loss of strength, construction moisture is an important consideration when building with CLT. This document aims to provide technical information to help architects, engineers, and builders assess the potential for wetting of CLT during building construction and identify appropriate actions to mitigate the risk.
The pre-air-drying of Korean pine before the high-temperature and low-humidity drying was shown to be effective in uniform moisture content distribution and prevention of surface check. Our results suggest that initial moisture content of the timber also plays important role in high-temperature and low-humidity drying method. The pre-air-drying also helps in the reduction of surface checks in Korean pine when compared to the Korean pine dried by only high-temperature and low-humidity. End-coating was not effective in the prevention of twist, shrinkage, case hardening and internal checks. The pre-air-drying reduces the internal tension stresses which occur during high-temperature and low-humidity drying thus decreasing case hardening and also preventing internal checks. The pre-air-drying decreases the moisture content and causes shrinkage which leads to increased twist in the Korean pine.
Cross-laminated timber (CLT) panels have potential market in North America for building mid-rise structures due to their good structural and seismic performance, lightweight, and prefabricated nature. However, to ensure long-term durability, the hygrothermal performance of CLT wall assemblies needs to be evaluated in terms of drying and wetting potential before their widespread adoption in North America. A test wall was constructed with initially wetted CLT panels, and monitored over a year. The drying behaviour of the panels was analysed, and results were compared to hygrothermal simulations. It was found from the field data that no tested wall assemblies in the given climate prevented the panels from drying in enough time to prevent decay initiation. The hygrothermal simulation program is capable of predicting general trends, and can predict if a wall be safe, but tends to be overly conservative. Further refinement of the model for wood is needed.
Le bois lamellé-croisé (CLT) est un produit massif de bois d’ingénierie qui est fabriqué à partir de multiples pièces de bois de dimension assemblées en couches orthogonales avec des adhésifs structuraux. Ce produit est conçu pour des conditions de service sèches et est couramment utilisé pour construire des planchers, des toits et des murs. Comme l’humidification prolongée du bois peut causer des taches, de la moisissure, des variations dimensionnelles excessives (parfois suffisantes pour provoquer la défaillance des attaches), et même la pourriture et la perte de résistance, l’humidité est un facteur important dans la
construction avec le CLT. Le présent document a pour but de fournir de l’information technique pouvant aider les architectes, les ingénieurs et les constructeurs à évaluer les risques d’humidification du CLT pendant la construction de bâtiments et à prendre les mesures appropriées pour atténuer ces risques.
Cross-laminated timber (CLT) panels have potential market in North America for building mid-rise or even taller structures due to their good structural and fire safety performance, light weight, and prefabricated nature. However, to ensure long-term durability when used in building enclosures, the hygrothermal performance of CLT wall assemblies needs to be evaluated in terms of wetting and drying potential. A test wall consisting of sixteen 0.6 m by 0.6 m CLT panels made of five different wood species (or species groups) and four different wall assemblies was constructed. The CLT panels were initially wetted with the moisture content (MC) in the surface layers approaching or exceeding 30%, and monitored for MCs and temperatures at different depths over one year in a building envelope test facility located in Waterloo, Ontario. The drying behaviour of these panels was analysed and the measured MCs over time were compared to simulation results using a commercial hygrothermal program. This field study showed that most of the CLT panels dried to below 26% within one month except for CLT walls with a low-permeance interior membrane, which indicated that none of the CLT walls would likely remain at a high MC level long enough to initiate decay under the conditions tested. The simulation results generally agree well with the field data at MCs below 26%. However, it was found that the hygrothermal simulation program tended to overestimate the MC in the centre of the panels by up to 5e10%, and simulated MCs at locations deep into the CLT panels were not as responsive to changes in ambient conditions, as the measurements indicated for assemblies with high exterior permeance.