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Mechanická analýza celodřevěných konstrukčních spojů
Milch, Jaromír
Traditional all wooden construction joints are currently widely used when historically valuable buildings are being reconstructed. These construction joints are indispensable and irreplaceable in order to maintain cultural heritage for our future generations. They underline the importance of the wooden structures and buildings, which in many cases might have incalculable historical, artistic as well as financial value. However, increased interest brings many challenges and potential risks that need to be taken into account and eliminated by appropriate solution(s). Adequate employment of these wooden joints requires a research-based approaches, which allows proper implementation within existing constructions while maintaining its reliability and safety. Main aim of preset doctoral thesis was to contribute to the development of suitable methods for analyzing mechanical behavior of all wooden construction joints, especially dowel joints, which are mainly used for reconstruction of damaged wooden elements or their parts. For such purposes, various methods (models), based on combination of theoretical, experimental and numerical approaches, has been used. This work was divided to a) basic mechanical tests of solid wood and b) complex finite element analyses of all wooden joints and constructions. Mechanical behavior in tension, compression, bending and shear was tested on small clear specimens made of spruce (Picea abies L. Karst.), beech (Fagus sylvatica L.) and oak (Quercus robur L.). Analyzed species were chosen as a most important historical as well as present European building materials. Mechanical response was captured using cameras in stereovision 3D configuration in order to obtain full-field displacement and strain data sets. Based on obtained data, material characteristics were determined and verified in frame of assembled material models for finite element analyses (FEA). Verified elasto-plastic material models were used as main material inputs for complex FEA for evaluation of mechanical response of joints and constructions subjected to load. Furthermore, material characteristics were used in calculations of mechanical properties of dowel joints. Numerical analyses were done using ANSYS software with parametric design language (APDL). Experimental results of single-shear dowel joints are in agreement with theoretical approach according to European Yield Method (EYM) theory, which was used for determination of joints and fasteners yield strength. FEA proved that assembled elasto-plastic material models can predict the ultimate strength even in complex tasks, and therefore, can be used for more reliable designing of wooden constructions and joints in variety of configurations.
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Mechanical properties of the lamellae materials
Vokatý, Vojtěch ; Gaff, Milan (advisor) ; Babiak, Marian (referee)
This thesis evaluated experimental research on the influence of selected factors (species, thickness, density, number of stress cycles) on the specified material characteristics (modulus of elasticity, modulus of rupture, limit of proportionality, bendability coefficient). The measured values were statistically evaluated and expressed in tables and graphs. Beech (Fagus Sylvatica L.) was selected to represent hardwood and aspen (Populus Tremula L.) softwood.
Tree species affects all observed characteristics. The results show that the modulus of elasticity increases with increasing densification of the material, but decreases with the increasing thickness of the material. A similar dependence is observed even with the modulus of rupture and limit of proportionality, which is also dependent on the number of cycles. The bendability coefficient is affected by material thickness.
It is expected that based on the evaluation of the results it will be possible to design materials with tailored properties.
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Principles targeted Edit the properties of layered materials
Houžvíček, Petr ; Gaff, Milan (advisor) ; Gašparík, Miroslav (referee)
Target of the thesis was an investigation of the influence of selected factors (tree species, thickness of material, type of glue and cyclic loading) and their combinations on strength properties of laminated lumber. This measured properties were: bending strength, modulus of elasticity, limit of proportionality, coefficient of bendability and shear strength of glued joint.
Most important factor for bending strength, modulus of elasticity and limit of proportionality was the tree species. For coefficient of bendability and shear strength of glued joint the most important was the material thickness. Influence of cyclic loading and type of glue, weren´t proved.
After that, we simulated our investigation which we made in computer program based on finite element method. The simulation corresponded just for thicker tested samples.
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