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Material properties of decayed wood of standing beech trees
Colledani, Pavel
The goal of this thesis was to determine how accurate acoustic tomography is when compared to mechanical testing and apply the results to usage in arboriculture in context of European region. For this purpose, two beech trees (Fagus sylvatica) from University Forest Enterprise Masarykův les - Křtiny in Babice nad Svitavou with fungal decay were subjected to acoustic tomography testing using FAKKOP ArborSonic device. After measurement, both trees were felled and two cross-cuts were taken from each trunk. Cross-sections were then divided into sample grids with five-centimetre sides and subjected to further acoustic testing. Density was also determined. Subsequently, samples were compressed in universal testing machine where maximum compression strength was determined. Samples were photographed in 0,5 second intervals and strain were computated from these photos in MercuryRT programme. From this testing, modulus od elasticity was determined. From velocities and density measurements, dynamic modulus of elasticity was determined. All values were statistically analysed a compared. The results show that acoustic tomography is a reliable method in compared to mechanical testing. Few limiting factors like white rot, open cavities and stage of decay were observed and taken into consideration when results were interpreted. White rot was discovered to be influencing mechanical properties while not affecting measured velocities of acoustic measurement. Early stages of white rot were found to be affecting density but not strength, effectively making wood stronger while lighter. Open cavities influenced tomography measurement to a large extend, making it unreliable compared to sample velocity measurement and mechanical testing. All discovered results could be applied to arboriculture profession in a European context.
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Využití alternativních surovin ve výrobě aglomerovaných materiálů pro stavby
Špavor, Oskar
The work dealt with the possibility of using straw for the production of large-area materials. The input material was wheat straw and lucerne. As a binder, a commonly used pMDI adhesive was used here to provide reference values for starch adhesive and lignosulfonate leachate. Before pressing the main formats (60x60 cm, 12 mm thick), test plates (15x15 cm, 12 mm thick) were pressed to examine the optimum pressing time, temperature and pressure. A temperature of 190 ° C and a pressing pressure of 3,5 MPa were chosen as the most suitable. Pressing main boards cause a number of problems with excess moisture released from the binder. All attempts to press the board are described in chapter 3.4 Pressing Individual Materials with Binders. During the pressing process, wheat straw was unable to absorb moisture released from the starch adhesive. After opening the press, the plate was board to pieces due to steam. A large blister was found in the middle of a wheat straw plate (dried to 4 %) with pMDI glue. Unfortunately, all attempts to make a board of wheat straw ended unsuccessfully. Lucerne (12% humidity) with pMDI glue was successfully pressed with a compression factor of 10 s / mm. The samples reached on average a modulus of elasticity of 3112 MPa, a modulus of strength of 17,89 MPa, an internal bonding of 0,46 MPa, a moisture absorption of 10,9% and a thickness swelling of 27,6%. Lucerne with lignosulfonate was pressed on the third attempt, when the lucerne moisture was 12% and compression factor of 40 s / mm. During pressing, 15 press relieves were performed after 30 seconds to remove excess steam. The samples reached a modulus of elasticity of 1914 MPa, a modulus of strength 93 MPa, an internal bonding of 0,03 MPa, and a moisture content of 12,2%. The swelling could not be measured here due to wetting of the samples. Lucerne (12% moisture) with starch glue was pressed with a compression factor of 40 s / mm. During pressing, 15 press relieves were performed after 30 seconds. The samples reached a modulus of elasticity of 1286 MPa, a modulus of strength of 3,01 MPa, internal bonding of 0,1 MPa, and a moisture content of 11,2%. Swelling could not be measured here due to wetting of samples.
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Vliv chemické a tepelné modifikace na mechanické vlastnosti bukového dřeva
Vodák, Michal
The presented diploma thesis is focused on the analysis of the influence of selected beech wood (Fagus sylvatica L.) modifications and its behavior under mechanical stress. Beech samples were modified with acetic anhydride, with melamine-formaldehyde resin and thermally modified using temperatures 180, 200 and 220 ° C. The shear moduli and shear strengh parallel and perpendicular to the grain, compression moduli a compression strenght parallel and perpendicular to the grain and 3point static bending moduli and strenght perpendicular to the grain were determined. The mechanical behavior of the modified wood was studied under various MC conditions, i.e., oven dried at 103 ± 2 °C to 0 % moistruce content, conditioned at 65 % relative humidity and 20 °C and conditioned at 90 % relative humidity and 20 °C. The digital image correlation (DIC) method was employed as a virtual extensometer to observe stress-strain diagrams. The results show a statistically significant effect of wood modification on mechanical behavior in the context of equilibrium moisture content. More significant percentage changes were observed for yield strength values compared to the modulus of elasticity. Acetylation of wood lowered the effect of moisture to a statistically insignificant value in the case of modulus of elasticity measured by 3point static bending. Wood acetylation also led to increase of the compressive strength perpendicular to the grain by about 100 %. All types of wood modifications have shown the potential for commercial use, even for structural applications. However, a specific method must be selected based on the requirments of designed construction. It is not possible to determine one modification method that would perform best across all applications.
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The Influence of different Types of Fiber-reinforcement on the Behavior of Concrete Slabs
Wünsche, Dominik ; Žítt, Petr (referee) ; Kocáb, Dalibor (advisor)
The bachelor‘s thesis deals with the issue of concrete, specifically self-compacting concrete, fiber concrete and other types of concrete used. The work consists of two parts, the theoretical one, which will deal with the properties of the concrete. It describes the individual test methods used in the practical part. The test methods are the ultrasonic pulse method, the resonance method, the static modulus of elasticity, the compressive strength, and especially flexural strength. The second part is a practical part, which is processed by an experiment. In the experimental part, it will be mainly about carrying out tests of self-compacting concrete slabs and concrete with the addition of steel fibers. Subsequently, selected characteristics of concrete are determined and the whole experiment is evaluated.
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Additional reinforcement of wood elements
Janoušek, Radek ; Vejpustek,, Zdeněk (referee) ; Vaněrek, Jan (advisor)
This diploma thesis deals with the possibilities of additional reinforcement of wooden elements using different types of BFRP materials. In the practical part, an experiment of reinforcing plywood with external reinforcement using BFRP fabrics with different basis weights was performed. As part of the strength tests performed, the specimens were subjected to bending and shear stresses. To verify the bonding quality of the plywood, the bodies were exposed to the effect of elevated temperature and a delamination test was performed to determine the bonding quality of the plywood joints. The achieved values were evaluated and compared with the available literature.
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Modification of silicate materials for floors
Šlechtický, Luboš ; Ing. Miroslav Šťenko, Ph.D., LB Cemix (referee) ; Šťastník, Stanislav (advisor)
The thesis is devoted to the issue of flooring materials, cement and plaster. In the first part are discussed general properties and general requirements for flooring, as well as presents the most important properties of selected flooring materials. The work is dedicated to the modulus of elasticity, adhesion to the substrate and strength parameters of the tested materials. It also evaluates the effects of redispersible polymer powders in silicate compositions intended for floors.
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Study of thermal resistance of reinforced wood members
Janoušek, Radek ; Krbila, Jaromír (referee) ; Vaněrek, Jan (advisor)
This bachelor's thesis studies the problem of thermal resistance of a system consisting of timber as a structural member with external strengthening in the form of carbon fibre reinforced polymer lamellas connected by various types of adhesives. Attention will be paid to the thermal resistance of reinforced timber members with subsequent mechanical load.
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Influence of multiple cyclic loading on the selected parameters of lightweight concrete
Alexa, Martin ; Misák, Petr (referee) ; Kocáb, Dalibor (advisor)
The diploma thesis deals with the observation of the values of selected parameters (especially the static modulus of elasticity) of light-weight concrete in compression before and after multiple cyclic loading. The deformation of test specimens during multiple cyclic loading were measured with resistive strain gauges. Test specimens (cylinders with a diameter of 150 mm and height of a 300 mm) were cyclically loaded and up to 4 500 loading cycles were performed. The aim of this thesis is assessment changes in the values of static modulus of elasticity depending on the number of loading cycles.
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