In wood-frame buildings of three or more stories, cumulative shrinkage can be significant and have an impact on the function and performance of finishes, openings, mechanical/electrical/plumbing (MEP) systems, and structural connections. However, as more designers look to wood-frame construction to improve the cost and sustainability of their mid-rise projects, many have learned that accommodating wood shrinkage is actually very straightforward. This publication will describe procedures for estimating wood shrinkage and provide detailing options that minimize its effects on building performance.
The current research investigated the delamination process of adhesively bonded hardwood (European beech) elements subject to changing climatic conditions. For the study of the long-term fracture mechanical behavior of gluedlaminated components under varying moisture content, the role of moisture development, time- and moisture-dependent responses are absolutely crucial. For this purpose, a 3D orthotropic hygro-elastic, plastic, visco-elastic, mechano-sorptive wood constitutive model with moisture-dependent material constants was presented in this work. Such a comprehensive material model is capable to capture the true historydependent stress states and deformations which are essential to achieve reliable design of timber structures. Besides the solid wood substrates, the adhesive material also influences the interface performance considerably. Hence, to gain further insight into the stresses and deformations generated in the bond-line, a general hygro-elastic, plastic, visco-elastic creep material model for adhesive was introduced as well. The associated numerical algorithms developed on the basis of additive decomposition of the total strain were formulated and implemented within the Abaqus Finite Element (FE) package. Functionality and performance of the proposed approach were evaluated by performing multiple verification simulations of wood components, under different combinations of mechanical loading and moisture variation. Moreover, the generality and efficiency of the presented approach was further demonstrated by conducting an application example of a hybrid wood element.
Wood preservation is an important issue for agricultural buildings with timber structure. This is among others due to their halfway opened construction, high level of moisture release from livestock breeding or storing goods. However, regarding the possibly high moisture content in the building structure and the potential threat caused by wood-destroying organisms, there is still a substantial need for research. The latest results of the research work carried out by Technical University of Munich, in cooperation with the Bavarian State Research Center for Agriculture, show that, for the most agricultural buildings built from spruce, no preventative chemical wood preservation is necessary to ensure a durable construction.
There is a need of more advanced analysis for studying how the long-term behaviour of glued laminated timber structures is affected by creep and by cyclic variations in climate. A beam theory is presented able to simulate the overall hygro-mechanical and visco-elastic behaviour of (inhomogeneous) glulam structures. Two frame structures subjected to both mechanical and cyclic environmental loading are analysed to illustrate the advantages the model involved can provide. The results indicate clearly both the (discontinuous) inhomogeneity of the glulam products and the variable moisture-load action that occurs to have a significant effect on deformations, section forces and stress distributions within the frame structures that were studied.
Cross-laminated timber (CLT) modular construction possesses the advantages of wood, such as excellent carbon storage and thermal insulation, and of modular construction, such as considerably reduced construction period and cost as well as high productivity. This study evaluates the hygrothermal performance of CLT walls considering modular construction in future climatic conditions. Firstly, CLT walls with plywood applied to a core layer were manufactured. A mock-up of a CLT building was produced and its construction process was analyzed. Hygrothermal behavior of the CLT walls was simulated using WUFI simulation program, and the predicted results were verified against measurements obtained from the mock-up experiment. Finally, the hygrothermal performance of the CLT wall was evaluated for four types of insulation and future climate in eight cities of USA. The coefficient of variation—root mean square error (CV(RMSE))—of the temperature and relative humidity inside the ply-lam CLT wall from mock-up experiments and simulation evaluation were 6.43% and 7.02%, respectively, which met the validation criteria. Based on the hygrothermal performance, the ply-lam CLT wall with extruded polystyrene insulation was evaluated as safe from moisture problems in all the eight cities considered in this study. However, the risk of mold growth in all regions and insulation types increased under climate change with a rise of average annual temperature.
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.
Through long-term measurements of climate data (temperature, relative humidity) and timber moisture content on large-span timber structures in buildings of typical construction type and use, data sets were generated which deliver information on the sequence and magnitude of seasonal variations. The measurement of moisture in different depths of the cross-section is of particular interest to draw conclusions on the size and speed of adjustment of the moisture distribution to changing climatic conditions. The moisture gradient has direct influence on the size of the internal stresses and possible damage potential. Similarly, the results provide a review and extension of the previous classification of buildings into use classes. They allow for a more precise indication of range of resulting equilibrium moisture content for the specific use, enabling the installation of timber elements with adjusted moisture content. The results of the research project also support the development of appropriate monitoring systems, which could be used in the form of early warning systems based on climate measurements.
The role of the building envelope research team in this project was to assess whether midrise wood-frame (LWF) and cross-laminated timber (CLT) building envelope solutions developed by the fire research team to meet the fire provisions of the National Building Code (NBC) 2010 Part 3 Fire Protection, would also meet the NBC Part 5 Environmental Separation requirements relating to the protection of the building envelope from excessive moisture and water accumulation. As well, these wood-based mid-rise envelope solutions were to be assessed for their ability to meet Part 3 Building Envelope of the National Energy Code for Buildings (NECB) 2011. Requirements relating to heat, air, moisture, and precipitation (HAMP) control by the building envelope are included in Part 5 Environmental Separation of the NBC 2010. Part 5 addresses all building types and occupancies referred to in Part 3, but unlike requirements for fire protection, this section of the code was written more recently and is generic, including requirements that are more objective-oriented rather than prescriptive requirements pegged to specific constructions systems. The investigated methodologies developed and adapted for this study took those code characteristics into account.
Journal of Sustainable Architecture and Civil Engineering
Notes
DOI link: https://doi.org/10.5755/j01.sace.25.2.22263
Summary
This paper focuses on cross-laminated timber (CLT) and how it is affected by the dynamic properties of moisture during installation in the cold climate of Estonia. The moisture safety principles are designed using a case study of comparable activities with 4D principles and on-site water content monitoring. On-site water content monitoring was done on the CLT elements that were installed and a parallel polygon specimen. Polygon testing was arranged with reduced size CLT elements subject to different conditions, with some exposed to the climate, some protected from precipitation, and some covered with film.
The moisture content (MC) of the uncovered horizontal CLT element that was exposed to the climate reached over 25% after higher precipitation and the MC after prolonged direct exposure can reach up to 40% in a week, giving a clear signal of high risk areas for moisture safety. Installing a partly weather protected CLT element without a preliminary roof is a high-risk arrangement, but is essentially possible in a cold climate. Moisture safety pre-planning and a lean strategy must be applied with timber construction.
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.
