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.
A study was conducted with the primary objective of gathering information for the development of a protocol for evaluating the surface quality of cross-laminated timber (CLT) products. The secondary objectives were to examine the effect of moisture content (MC) reduction on the development of surface checks and gaps, and find ways of minimizing the checking problems in CLT panels. The wood materials used for the CLT samples were rough-sawn Select grade Hem-Fir boards 25 x 152 mm (1 x 6 inches). Polyurethane was the adhesive used. The development of checks and gaps were evaluated after drying at two temperature levels at ambient relative humidity (RH).
The checks and gaps, as a result of drying to 6% to 10% MC from an initial MC of 13%, occurred randomly depending upon the characteristics of the wood and the manner in which the outer laminas were laid up in the panel. Suggestions are made for minimizing checking and gap problems in CLT panels. The checks and gaps close when the panels are exposed to higher humidity.
Guidelines were proposed for the development of a protocol for classifying CLT panels into appearance grades in terms of the severity of checks and gaps. The grades can be based on the estimated dimensions of the checks and gaps, their frequency, and the number of laminas in which they appear.
The objective of the task is to select, from the 679 locations in Table C-2 of the 2010 National Building Code of Canada (NBC 2010), several representative locations for which long-term historical weather data exists. This information from these locations can subsequently be used to determine the exterior boundary conditions for input files for hygrothermal simulation programs and hygrothermal testing in the laboratory.
This report discusses the selection of locations for the hygrothermal simulation task of the project on Mid-rise Wood Buildings and the determination of spray-rates and pressure differentials for the water penetration testing portion of the project.
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).
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.
Nail-laminated timber (NLT) is a large built-up member often used as interior structural members for floors, roofs, walls, and elevator/stair shafts. Because prolonged wetting of wood may cause staining, mould, excessive dimensional change (sometimes enough to fail fasteners), and even result in decay and loss of strength, construction moisture is an important consideration when building with NLT. This document aims to provide technical information to help architects, engineers, and builders assess the potential for wetting of NLT during building construction and identify appropriate actions to mitigate the risks.
Many academic studies over the years have confirmed that mechano-sorptive (MS) creep is an inherent characteristic of wood. Unlike solid wood, bond lines are introduced into laminated veneer lumber (LVL), creating a laminated structure with different hygroscopicity. What are the effects of these differences on the MS creep of LVL? In this study, three groups of well-matched LVL samples were subjected to four-point bending loading within different relative humidity cycles. For each group, the applied load ranged from 15% to 35% of the short-term fracture load. The results showed that after the first hygroscopic process, LVL showed irreversible expansion (0.11 mm) and a relatively slow moisture adsorption rate. These made it difficult for LVL to show partial creep recovery during the first adsorption process no matter how low the load level was, while solid wood showed partial creep recovery when the load level was = 25%. The following creep behavior of LVL was similar to that of solid wood: partial creep recovery started from the second adsorption stage when a moderate load level was applied.
The USDA Forest Products Laboratory (FPL) has, for the past two years, been assisting in removing technical barriers to the use of CLT and trying to develop interest in the United States for its utilization. Coincidentally, Promega Corporation, a leader in providing innovative solutions and technical support to the life sciences industry, is currently constructing a new facility in Fitchburg, Wisconsin, that features CLT. This is the first large-scale commercial utilization of CLT in the United States using CLT manufactured in North America. As with any new building system, it is important for the design and construction community to have information on how CLT is installed and how it performs.
The objectives of this research are twofold: (1) to document the CLT installation process with photography and video and (2) to install sensors in the CLT panels and collect data on in-service moisture and temperature conditions.
This paper deals with assessment of glulam twinned columns to beam circular bolted connection. This kind of connection is used for embedded assembly. Because of the moisture content variations, cracks often occur in the direction parallel to the grain. The aim of the study is to understand the mechanism responsible of the cracks happening. In the same time, another aim of this study is to evaluate the residual resistance of a damaged assembly. The assembly has been designed according to Eurocode 5. Two different initial conditions have been tested. For the first assembly, the columns and the beam have been dried before machining and tested dry. For the second assembly, the beam was wet and the columns were dry before machining, then the assembly was tested dry. The difference of moisture content implies a huge tensile strain in the direction perpendicular to the grain of the columns before loading. In order to qualify the assembly behavior, strain gauges techniques have been used. This analysis allows a better understanding of the phenomenon of cracks initiation and propagation due to the coupled effect of shrinkage/swelling and loading.
Although cross-laminated timber (CLT) offers greatly improved directional stability against moisture changes compared to lumber, some layup dependent directional differences still remain. Furthermore, even under a purely homogeneous distributed moisture change strong deformations appear along the boundaries, which show a decrease of swelling/shrinkage towards the inside of CLT panels. Metrological determination of this behavior is still a challenging task and involves long-lasting moisture content conditioning and typically manual measurements. This limits the amount of measurable data-points and thus the gain-able insights.
We apply a recently introduced computer vision technique based on optical flow from scan images to measure surface deformation fields of various CLT specimens with different layups. This allows us to measure the change of average differential swelling and shrinkage coefficients throughout the cross section and visualize them as curves with high resolution. We gain measurements for each image pixel and demonstrate good matching to previously published manual single-point measurements.
Furthermore, we analyze various specimens specifically built to allow for investigations of the aforementioned boundary effects. Using the computer vision approach we are able to show how the combination of homogeneous deformations and boundary effects leads to the resulting deformations observable with manual methods.
