This study deals with the impact of silicon-based chemicals on selected physical and mechanical properties of wood. Wood of European beech and Scots pine was the testing material used for impregnation using water glass and commercial product Lukofob EVO 50. The impact of the treatment on dimensional stability, bending strength and modulus of elasticity was tested. Wood density was also evaluated. Although the modification using silicon-based staffs resulted in a statistically significant decrease in swelling for both of the tested species, the positive effect of the treatment was accompanied by a decrease in the strength and stiffness of wood. Water glass had a stronger effect on the tested properties from the chemicals we used in our research.
The decrease is supposed of the coniferous assortments supply due to running changes of tree species composition in the Czech forests as well as due to the environmental changes in the next decades. The Norway spruce (Picea abies /L./ Karst.) is the most endangered species. The year timber supply decrease of this species is supposed in an extent of 0.9 mil.m3 in the next two decades (2013 – 2032) and more than 1 mil. m3 for all conifers. Cultivation of Douglas-fir (Pseudotsuga menziesii /Mirb./ Franco) can substitute N. spruce on specific sites and so eliminate partially the timber supply decline in the future. The cultivation of Douglas-fir could lead to increase of the plantation area from 5,800 ha (today) to the extent of 49,616 – 163,713 ha respecting legislative restrictions and recommendations of general management plans. This can represent increased timber increment of 300,000 – 650,000 m3 per year and substantially mitigate the coniferous timber supply fall in the next decades.
The awareness of the need to protect wooden members dates back to the Middle Ages when the most common material for the protection of wood was oxblood. At present, there is a huge variety of biocidal chemical agents for wood protection available (such as Lignofix, Bochemit). Nanotextiles represent a novel method of enhanced biocidal protection of historic wood which has been intensively verified at the Faculty of Civil Engineering, CTU in Prague within the NAKI DG16P02M055 research. The paper will present partial results of experimental research into the effects of selected nanotextiles on the surface of historic wood applied for the purpose of biocidal protection. The research included the verification of the efficiency of nanotextiles without dopants and with dopants of Ag and TiO2 nanoparticles. Surprisingly, a higher biocidal efficiency of nanotextiles without dopants was reached than in the case of nanotextiles with dopants.
Currently, the trend of using untreated wood elements in the exterior is becoming more progressive. The rainwater nevertheless needs to be recognized as an important factor increasing photo-degradation of wood and causing other damages as splits, cracks and deformations. The aim of this work is to determine the influence of initial stages of weathering on wetting properties of wood surfaces evaluated by the contact angle measurements using goniometer Krüss DSA 30E. Nine wood species were tested during 12 months of weathering: spruce, larch, pine, Douglas fir, oak, black locust, maple, alder and poplar. The lower decrease of the contact angle of water drop was observed on maple, alder and black locust surfaces, which predicts higher durability and slower degradation during weathering. On the contrary, the higher decrease of contact angle and higher hydrophilicity of wood surfaces was observed on all softwoods and oak and poplar as well.
The article describes behaviour of the structure of a prefabricated winder wooden staircase with central stringer on the material basis of Scots pine (Pinus sylvestris L.). It focuses on static behaviour of this structure. An analysis was performed with the use of 3D numerical modelling with the finite element method using ANSYS calculation system. The numerical analysis with an orthotropic material model and Hoffman and Tsai-Wu interactive failure criteria showed critical points of this type of analysed staircase. Subsequently, selected critical points were experimentally tested for static loading on models of wooden fragments of the staircase in the scale of 1:1. Experimental tests and numerical analyses pointed out the importanceof a suitable choice of a material model of wood and the necessity to pay particular attention to designing of these points. The results and conclusions could be helpful for designing of a prefabricated winder wooden staircase with the central stringer.
The article deals with research of joints with glued-in threaded rods. The introduction provides a brief presentation of the issue. The first part focuses on axially loaded glued-in threaded rods. The second part explains the behaviour of joints with glued-in rods loaded by bending moment. Theoretical analysis was performed on models based on the finite element method. Verification of theoretical results was realized by practical experiments. Tensile tests were carried out on timber blocks with glued-in bars to verify the depth of affixing. Furthermore, the resistance in bending was confirmed on actual beams with glued-in bars in the middle of the span. Results and the follow-up work are summarized in the conclusion.
The content of this article is to analyse destructive testing results of longitudinal solid wood joints of structural size beams with internal and external glued wood-based panels (plywood) stressed in bending, which was mostly focused on simulating the effect of the glued line thickness (1 and 3 mm) and the influence of contact surfaces of longitudinally connected elements when bending loads. The aim of this article is to compare the carrying capacity and the joint real behaviour under load with values obtained using numerical modelling and calculation according to valid standards.
The primary aim of the paper is to characterize the emissions of volatile organic compounds (VOC) in the indoor air of wood-based buildings in the Krkonoše Mts. region in relation to season, age of the building, air moisture content and engineering composition of building materials. It aims to identify the impact of important factors on the amount and content of VOC emitted into indoor air. The experimental part focuses on the assessment of influence of applied wood-based materials in the wood-based buildings on the quantity and quality of VOC emissions in indoor air. The second aim is to determine the impact of age of a building and the time of VOC measuring on the amount and content of emitted VOC, particularly on the amount of emitted terpenes and aldehydes. VOC emissions were analysed by gas chromatograph Agilent GC 6890 N with a mass spectrometer with cryofocusation, thermal desorption and library of spectra NIS 05.
The article analyses the air leakage rate in 203 newly constructed low-energy and passive wood-based residential buildings in the Czech Republic. The most frequent air leakage points were analysed in the buildings measured, and the development of the air leakage rate in the period monitored (2006-2014) was evaluated. A significant decrease in air leakage rate values was found out in low-energy buildings, while the results for passive buildings were more or less steady within the period in question. Further, airtightness of envelopes of low-energy buildings not equipped with a mechanical ventilation system with heat recovery reached, in some cases, values indicating that recommended values of the overall air leakage required by hygienic regulations are not ensured.
The thesis focuses on the matter of thermal bridges in case of wooden panel structures, both in case of low-energy and passive structure-standard. Thermography was used for localization of critical areas of structures – details of corner joints of external walls and ceiling connections. The values subject to comparison are the linear coefficient of heat penetration from the exterior and the lowest interior surface temperature. This results in the overall comparison of both the structures as well as elimination of the excessive heat flow, whereas the difference in detail of corner joints of external walls is 0.03 W.(m.K)-1 for both, and the difference in detail of the ceiling connections equals 0.07 and 0.08 W.(m.K)-1 respectively. The difference in the lowest interior surface temperature in detail of corner joints of external walls for both structures equals 1.34 and 2.99°C respectively, and in the detail of the ceiling connections the difference is 2.45°C.
This contribution focuses on the verification of temperature and moisture content conditions inside perimeter walls of timber buildings as regards the temperature and humidity requirements in buildings intended for permanent residence. We assessed: a simple perimeter wall of solid timber, a wall of glued BSH profiles, a wall of an existing log building with additional thermal insulation in two options, and a sandwich log wall with a layer of embedded insulation. This study contrasts theoretical calculations with the values measured in a real buildings. The effect of the humidity changes on the strength and stability of dowelled joints is analysed.
The article discusses the changes in diffusion properties of wood and wood-based materials. These changes are caused by excessive moisture content within the materials and the consequent possible attack by wood-destroying pests. Wood-destroying pests in this case are represented by microscopic filamentous fungi (i.e. mould), which slightly changes and deteriorates both, the characteristics of wood and wood-based materials, and the environment humans live in. This paper discusses the theory and application of microwave radiation and the experimental optimization of radiation to sterilize these biotic factors. Furthermore, the article describes the experiments conducted at the Faculty of Civil Engineering, demonstrating the results of sterilization process with regards microscopic fungi that occur in building materials. By analysing the results of the research, the optimum intensity of microwave emitters and necessary lengths of irradiation times were determined.
In general, building constructions containing wood elements are moisture sensitive. To increase the knowledge about their hygrothermal performance accompanied with assessments of risk of mold growth and other degradation mechanisms a set of analytical methods is typically used: standard calculation or more advanced mathematical models, laboratory measurements and field observations. Nevertheless, in some cases such approach seems not to be sufficient. Full size testing under controlled and long-time stable boundary conditions is needed in order to get more complex picture about the real performance and risks. In the first part, the paper informs about hygrothermal problems and mold growth modelling. The key part of the paper deals with methodology and technique available at University Centre for Energy Efficient Buildings: Full size façade openings for placing different assemblies of building envelopes with wood elements and facility with crawl-space type foundations. Furthermore, laboratory experiments and measurements together with in-situ monitoring as example are presented. The paper discusses combinations of advanced modelling used for design of experiments on one hand with expected results from full size controlled testing on the other hand. Classification of mold growth risk can represent an efficient way of expression of overall quality in this respect. First results are presented here for illustration. Paper concludes that coordinated combination of different research techniques can bring new knowledge in understanding the processes leading to deterioration of wood elements in building construction.
The paper describes experimental research in the real behaviour of connections and its application to the design and realization of new types of timber structures. According to the connection type, primarily dowelled joints with slotted-in steel plates made from solid and glulam timber have been examined. A vital factor in designing joints of timber structures is respecting wood properties related to its changes in humidity. It is namely the case of strength changes as well as volume changes in particular directions. The experimental tests have been used to evaluate the influence of material strength, diameter and dowel number on the load-bearing capacity of joints. Substantial strengthening of joint’s load-bearing capacity can be attained by eliminating transverse tensile stresses in the region of dowels. Thus the conclusions derived from the experimental research and from the real behaviour have been implemented by the authors to develop new types of timber structures.
The article describes the thermal – technical point of four wooden constructions in the passive standard, when one of the constructions was tested in an accredited laboratory 1007.4 thermal – technical diagnostics. The sample was made according to the laboratory´s requirement 1700 x 1700 mm and tested according to the test harmonized standard ČSN EN ISO 8990: 1994 Thermal insulation – Determination of thermal transmission properties in the steady state temperature – calibration and guarded hot box. The object of the tests was to declare heat thermal transmittance value – U value based on the measured surface temperatures (θsi) and energy consumption. Thermal resistance and thermal transmittance were empirically calculated according to the measured and standard values in accordance of the CSN 73 0540: 2011. Thermal protection of buildings. The other three structures will be structurally modified to reflect this normative value Upas 20 = 0.12 – 0.18 (W.m-2 . K-1) and ensure their cost optimization.