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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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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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Probabilistic model for textile concrete reinforcement and comparison with experiments
Lomič, Jiří ; Rypl, Rostislav (referee) ; Vořechovský, Miroslav (advisor)
The scope of the presented bachelor’s thesis was the establishment of a probabilistic model for material strength of textile reinforcement used for textile reinforced concrete. This reinforcement is composed of AR-glass multi-filament yarns. The goal of this thesis was to determine the potential weak spot of the textile yarn and evaluate its strength in overall. The weak spot could have been a lateral cross-connection, which narrowed the textile yarn at several locations. Another thing of interest was the observation of statistical size effect with the increasing length of textile yarn. In order to properly fit the numerical model to real behavior of multi-filament yarns, five series of experimental tensile testing has been executed in laboratory. Each series consisted of 8-10 specimens and had a different yarn length. Maximum tensile force and maximum deformation have been measured to obtain L-D diagrams for each specimen. Measured data were statistically analyzed and gave the information necessary for the identification of probabilistic model parameters. This parameter estimation has been carried out with the help of numerical and optimization methods included in Python programming algorithms. The problem statement resulted in a combination of model parameters describing the textile yarn behavior. The statistical size effect was observed corresponding to the Weibull theory. The performed study showed that the failure of the textile yarn depends on material strength of its filaments. There are no load concentrators at the location of lateral cross-connections affecting the yarn failure.
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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.
|
|
|
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.
|
|
|
Probabilistic model for textile concrete reinforcement and comparison with experiments
Lomič, Jiří ; Rypl, Rostislav (referee) ; Vořechovský, Miroslav (advisor)
The scope of the presented bachelor’s thesis was the establishment of a probabilistic model for material strength of textile reinforcement used for textile reinforced concrete. This reinforcement is composed of AR-glass multi-filament yarns. The goal of this thesis was to determine the potential weak spot of the textile yarn and evaluate its strength in overall. The weak spot could have been a lateral cross-connection, which narrowed the textile yarn at several locations. Another thing of interest was the observation of statistical size effect with the increasing length of textile yarn. In order to properly fit the numerical model to real behavior of multi-filament yarns, five series of experimental tensile testing has been executed in laboratory. Each series consisted of 8-10 specimens and had a different yarn length. Maximum tensile force and maximum deformation have been measured to obtain L-D diagrams for each specimen. Measured data were statistically analyzed and gave the information necessary for the identification of probabilistic model parameters. This parameter estimation has been carried out with the help of numerical and optimization methods included in Python programming algorithms. The problem statement resulted in a combination of model parameters describing the textile yarn behavior. The statistical size effect was observed corresponding to the Weibull theory. The performed study showed that the failure of the textile yarn depends on material strength of its filaments. There are no load concentrators at the location of lateral cross-connections affecting the yarn failure.
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