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Stochastic discrete modeling of progressive damage of concrete structures
Kučera, Michal ; Sadílek, Václav (referee) ; Vořechovský, Miroslav (advisor)
The work focuses on the use of deterministic discrete modeling with representation of spatial randomness in material parameters to simulate a series of experimental tests of concrete specimens in the shape of a dog bone, loaded in excentric uniaxial tension. The main focus is on the influence of the size of the structure on its mechanical properties, especially nominal strength (Size effect). The specimens are modeled as a plane stress problem using available discrete computational methods.
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Application of kriging in engineering problems with uncertainties
Tvrzník, Jakub ; Lehký, David (referee) ; Vořechovský, Miroslav (advisor)
The presented bachelor thesis aims at interpolation method called kriging, which is based on regression of values measured in the surroundings. Kriging is based on the idea that interpolated function is one realization of a random field. Using this method we can quantify the estimates of functional values at the surrounding points, including estimation errors at each point. At the same tame, kriging respects the exact measured values and the interpolation passes through them. The practical part demonstrates the application of method to engineering tasks, where the measured values are distributed randomly. In other examples, the measured values are distributed by using a grid.
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Analysis of fracture of quasibrittle materials using numerical modelling and acoustic/electromagnetic emission
Vodák, Ondřej ; Vořechovský, Miroslav (referee) ; Veselý, Václav (advisor)
This master thesis gives overview of non-destructive tests of concrete and provides detailed information concerning the acoustic and electromagnetic emission during monitoring of concrete failure. Conducted loading tests of plain concrete specimens are described in the thesis together with the performed numerical simulations of these tests in the software ATENA. The simulation results of concrete failure are analysed in detail and compared with the experimental results recording failure processes with the help of acoustic and electromagnetic emission. The majority of simulation results in software ATENA 3D show good agreement with the recorded data.
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Shear strength of textile reinforced concrete members
Lomič, Jiří ; Rypl, Rostislav (referee) ; Vořechovský, Miroslav (advisor)
The scope of the presented Diploma thesis was the establishment of calculation model for shear design of textile reinforced concrete members with rectangular cross-section. To accomplish this task, it was necessary to acquire the knowledge of the principles of shear design for steel reinforced concrete and existing design methods for textile reinforced concrete. Based on these principles, an experiment was designed as 3-point bending test to obtain values of acting shear force in textile reinforced concrete beams. These beams were filled with textile reinforcement made of carbon and alkali resistant glass and cast in the laboratory of the Solidian Company. An important factor for the experiment design was the a/d ratio which was constant for all tested beams. The value of acting shear force as well as of concrete compressive strength was obtained from each experiment. These values were used for the optimization of mathematical equation for the shear design of textile reinforced concrete members with rectangular cross-section. This equation was first analyzed to gain the knowledge of every influential factor. After, the coefficient CRm,c was determined from the experimental data using the methods of optimization. The problem statement resulted in the formula for shear design of textile reinforced concrete members with rectangular cross-section which may be applied with respect to the conditions of usability of the shear model.
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Comparison of localization limiters for strain-softening
Květoň, Josef ; Vořechovský, Miroslav (referee) ; Eliáš, Jan (advisor)
It is well known, that simulation of crack propagation using the finite element method is dependent on mesh discretization. The thesis compares two approaches, that are designed to reduce the mesh influence: (I) the crack band model and (II) the nonlocal model. These localization limiters are applied to simulate three-point-bent beam with and without notch. The model of the beam is made with several variants of mesh discretization differing in finite element size and inclination. Performance of both localization limiters is discussed.
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A dynamical particle system as a driver for optimal statistical sampling
Mašek, Jan ; Šejnoha,, Jiří (referee) ; Kruis,, Jaroslav (referee) ; Vořechovský, Miroslav (advisor)
The presented doctoral thesis aims at development a new efficient tool for optimization of uniformity of point samples. One of use-cases of these point sets is the usage as optimized sets of integration points in statistical analyses of computer models using Monte Carlo type integration. It is well known that the pursuit of uniformly distributed sets of integration points is the only possible way of decreasing the error of estimation of an integral over an unknown function. The tasks of the work concern a survey of currently used criteria for evaluation and/or optimization of uniformity of point sets. A critical evaluation of their properties is presented, leading to suggestions towards improvements in spatial and statistical uniformity of resulting samples. A refined variant of the general formulation of the phi optimization criterion has been derived by incorporating the periodically repeated design domain along with a scale-independent behavior of the criterion. Based on a notion of a physical analogy between a set of sampling points and a dynamical system of mutually repelling particles, a hyper-dimensional N-body system has been selected to be the driver of the developed optimization tool. Because the simulation of such a dynamical system is known to be a computationally intensive task, an efficient solution using the massively parallel GPGPU platform Nvidia CUDA has been developed. An intensive study of properties of this complex architecture turned out as necessary to fully exploit the possible solution speedup.
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Multi-filament yarns testing for textile-reinforced concrete
Kaděrová, Jana ; Seitl,, Stanislav (referee) ; Vořechovský, Miroslav (advisor)
The scope of the presented master thesis was the experimental study of multi-filament yarns made of AR-glass and used for textile-reinforced concrete. The behavior under the tensile loading was investigated by laboratory tests. A high number of yarn specimens (over 300) of six different lengths (from 1 cm to 74 cm) was tested to obtain statistically significant data which were subsequently corrected and statistically processed. The numerical model of the multi-filament bundle was studied and applied for prediction of the yarn performance and for later results interpretation. The model of n parallel filaments describes the behavior of a bundle with varying parameters representing different sources of disorder of the response and provides the qualitative information about the influence of their randomization on the overall bundle response. The aim of the carried experiment was to validate the model presumptions and to identify the model parameters to fit the real load-displacement curves. Unfortunately, due to unsuccessful correction of measured displacements devalued by additional non-linear contribution of the unstiff experiment device the load-displacement diagrams were not applicable to model parameters identification. The statistical evaluation was carried only for the maximal load values and the effect of the specimen size (length) on its strength was demonstrated. The size effect curve did not exclude the existence of spatial correlation of material mechanical properties modifying the classical statistical Weibull theory.
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Simulation of concrete fracture using nonlocal model
Květoň, Josef ; Vořechovský, Miroslav (referee) ; Eliáš, Jan (advisor)
The thesis deals with nonlocal model simulations of the three-point-bening test series. The model is applied to set of beams of variable size and notch depth. The intention is to identify such parameters that would provide the response of the nonlocal model similar to experimental data from the comprehensive fracture tests performed at the Northwestern University. Size and shape of the process zone are estimated from the discrete model results and according to that the parameters of weight function and material for the nonlocal model are identified. Results obtained with the model are compared to the experimental data.
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Tensile strength of fibrous yarns and composites
Rypl, Rostislav ; Šejnoha,, Michal (referee) ; Zeman,, Jan (referee) ; Vořechovský, Miroslav (advisor)
Technical textiles play a highly important role in today's material engineering. In fibrous composites, which are being applied in a number of industrial branches ranging from aviation to civil engineering, technical textiles are used as the reinforcing or toughening constituent. With growing number of production facilities for fibrous materials, the need for standardized and reproducible quality control procedures becomes urgent. The present thesis addresses the issue of tensile strength of high-modulus multifilament yarns both from the theoretical and experimental point of view. In both these aspects, novel approaches are introduced. Regarding the theoretical strength of fibrous yarns, a model for the length dependent tensile strength is formulated, which distinguishes three asymptotes of the mean strength size effect curve. The transition between the model of independent parallel fibers applicable for smaller gauge lengths and the chain-of-bundles model applicable for longer gauge lengths is emphasized in particular. It is found that the transition depends on the stress transfer or anchorage length of filaments and can be identified experimentally by means of standard tensile tests at different gauge lengths. In the experimental part of the thesis, the issue of stress concentration in the clamping has been addressed. High-modulus yarns with brittle filaments are very sensitive to stress concentrations when loaded in tension making the use of traditional tensile test methods difficult. A novel clamp adapter for the Statimat 4U yarn tensile test machine (producer: Textechno GmbH) has been developed and a prototype has been built. A test series comparing yarns strengths tested with the clamp adapter and with commonly used test methods has been performed and the results are discussed. Furthermore, they are compared with theoretical values using the Daniels' statistical fiber-bundle model.
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