The diploma thesis deals with the possibilities of evaluating the degradation of mechanical resistance of non-air-entrained concrete in the structure by frost cycles. The first part is focused on concrete, its resistance and test methods. This is followed by the definition of frost resistance, the effects of freeze-thaw on concrete at all stages of its service life and the possibilities of determining freeze-thaw resistance according to current standards. It describes in more detail selected test methods for determining frost resistance. In the practical part, it focuses on the determination of degradation resistance of test specimens made in molds and taken from the structure using reference and non-reference methods. In conclusion, it compares the different test methods and their suitability for the determination of freeze-thaw resistance.

The modulus of elasticity is one of the basic characteristics of concrete defining elastic deformation of concrete and it plays a significant role in the static design of structures. Due to current trends in concrete technology, offering a wide variability in the proposals of the composition of concrete, there are changes not only in strength characteristics but also in the modulus of elasticity of concrete. The aim of this doctoral thesis is to study the dependence of different compositions on modulus of elasticity of concrete. Design of concrete composition is prepared with respect to the use of different types of cement, mineral admixtures, types and fractions of aggregates. The work is mainly focused on the determination of static modulus of elasticity in compression with the addition of dynamic modules. In the first phase determined modulus of elasticity are compared with tabulated values according to Eurocode 2, which are derived for the specific strength class of concrete. Part of this work is the compilation of the main technological aspects of concrete which can favorably affect the modulus of elasticity.

Soil-cement is an integral part of pavement design, especially in areas that are aggregate deprived, such as Mississippi. Current designs are reliant on the relationship of unconfined compressive strength (UCS) to other mechanical properties. The other properties discussed in this dissertation are Modulus of Elasticity (E), Indirect Tensile Strength (St), and Modulus of Rupture (MOR). This dissertation includes a comprehensive review of past design methods and mechanical property relationships. While some mechanical property relationships were shown to be well understood (i.e. St to UCS), others were not as accurate, especially for the later life mechanical properties (i.e. MOR to UCS and E to UCS). This dissertation investigates the Plastic Mold (PM) Compaction (PM) Device and its ability to measure mechanical property relationships (UCS, E, St) for soil-cement as well as different materials, such as lime stabilized subgrade and Cold in Place Recycling (CIR) stabilized with cement. These mechanical property relationships were compared to soil-cement beam specimens, which are capable of being tested for the four previously mentioned mechanical properties from an individual specimen. Finally to have a better understanding of the later life mechanical properties and their relationships, PM and beam specimens were exposed to elevated temperatures to forecast out how these properties interrelate over time. These mechanical property values and relationship were then compared to Mississippi field cores ranging from 10 to 54 years old. These protocols, beam and elevated curing, were able to replicate what was seen for pavement cores that were extracted after decades of service. Over 1300 specimens were testing showing how these mechanical properties interacted from early ages and throughout a pavement’s life.

The flexural and tensile properties of visually graded southern yellow pine lumber were modeled. Longitudinal and transverse vibration techniques and proof-loading bending tests were used to assess the flexural and tensile properties of southern pine lumber. The properties evaluated were dynamic modulus of elasticity (dMOE), static modulus of elasticity (Eb), tension modulus of elasticity (Et), and ultimate tensile stress (UTS). The tensile properties were evaluated in the direction parallel to the grain. This study presents the results of tests conducted on No. 2 2 × 6 and 2 × 10 southern pine lumber of two different lengths (14 ft. and 16 ft.). The results of the analysis show that nondestructive testing techniques are excellent to assess Et and Eb. Moderate relationships were found between dMOE and UTS and between Eb and UTS. Improvements in the prediction of UTS were done with the inclusion of additional parameters into the model. The combination of dMOE, density, and frequency domain area (FDA) generated the highest coefficient of determination for UTS. The distributions of flexural and tensile properties were analyzed for the goodness of fit. Normal distribution was found for Eb data whereas the lognormal distribution was the best fit for the tensile properties.

No description available.

The subject of the study is a titanium implant. The research method consists in the approximate solution of the boundary value problem by the finite element method in the ABAQUS software module. A patent and literature search in the field of application of additive technologies in the production of implants. The first section presents the results of the review. Were considered methods of additive manufacturing and methods of testing porous materials, the results are described in the second section. A description of the test for precipitation of a porous implant and a finite element simulation of the process of precipitation of cellular material have been carried out. As a result, the distribution scheme of the parameters of the stress-strain state was constructed, which allows estimating dangerous sections from the standpoint of structural failure. The obtained data can be applied in building the architecture of a set of unit cells with a description of the stress-strain state. / Предметом исследования является титановый имплантат. Метод исследования состоит в приближенном решении краевой задачи методом конечных элементов в программном модуле ABAQUS. Проведен патентно-литературный поиск в области применения аддитивных технологий в производстве имплантатов. В первом разделе представлены результаты обзора. Были рассмотрены методы аддитивного производства и способы испытания пористых материалов, результаты описаны во втором разделе. Проведено описание испытания на осадку пористого имплантата и конечно-элементное моделирование процесса осадки ячеистого материала. В результате чего была построена схема распределения параметров напряженно-деформированного состояния, которая позволяет оценить опасные сечения с позиции разрушения конструкции. Полученные данные могут быть применены в построении архитектуры набора элементарных ячеек с описанием напряженно-деформированного состояния.

Three components, a pallet, packaging, and material handling equipment, of the unit load portion of the supply chain are physically and mechanically interacting during product storage and shipping. Understanding the interactions between two primary components, a pallet and packaging, in a unit load is a key step towards supply chain cost reduction and workplace safety improvement. Designing a unit load without considering physical and mechanical interactions, between those two components, can result in human injury or death caused from a unsafe workplace environment and increased supply chain operating costs, due to product damage, high packaging cost, disposal expense, and waste of natural resources. This research is directed towards developing predictive models of the compressive stress distributions using the principle of the beam on an elastic foundation and experimentally quantifying the compressive stress distributions. The overall objective of this study is to develop a model that predicts compressive stress distributions at the interface between a pallet deck and packaging as a function of: pallet deck stiffness, packaging stiffness, and pallet joint fixity. The developed models were validated by comparison to the results of physical testing of the unit load section. Design variables required for modeling included Modulus of Elasticity (MOE) of pallet deckboards, Rotation Modulus (RM) for nailed joints, and packaging stiffness. Predictive models of the compressive stress distributions were non-uniformly distributed across the interface between pallet deckboards and packaging. Maximum compressive stresses were observed at the deckboard ends over stringer segments. All predictive compressive stress distributions were influenced by pallet deck stiffness, packaging stiffness, and joint fixity. The less the joint fixity the greater the pallet deck deflection. The stiffer deckboards are more sensitive to joint fixity. For predictive compressive stress distribution models, the measure of the stress concentrations was the Compressive Stress Intensity Factor (SIF), which was the ratio of the estimated maximum compressive stress to the applied stress. Less stiff pallets and stiffer packaging resulted in greater SIF for all end condition models. SIF was reduced by stiffer joint, stiffer pallet deck and more flexible packaging. The stiffer the pallet deck and pallet joint the greater the effective bearing area. The lower stiffness packaging resulted in the greater effective bearing area with all three packages. The predicted effective bearing area was more influenced by pallet deck stiffness than the packaging stiffness. The developed prediction models were validated by comparison to experimental results. All prediction models fell within 95% confidence bounds except the 3/8-inch deck with free ends and 3/4-inch deck with fixed ends. The difference between predicted and measured results was due to a limitation in pressure sensor range and test specimen construction for the free end model and fixed end model, respectively. The results show effects of pallet deck stiffness and packaging stiffness on SIFs with percentage changes ranging from 2 to 26% (absolute value of change) for all three end conditions. The sensitivity study concluded that changing both pallet deck stiffness and packaging stiffness more significantly influenced the SIFs than bearing areas. / Ph. D.

High-strength concrete (HSC) belongs in the recent years to frequently used types of concrete. It allows realization of static challenging structures and also shows due to its dense structure greater durability especially against aggressive media. Currently HSC construction realization abroad is not exceptional. It’s using in the Czech Republic is still limited. When realized, then in a small scale in civil engineering works. The realization of high-strength concrete structures is closely related with the concrete construction quality verification. Good efficiency of the quality control methods can provide non-destructive testing methods (NDT), especially when investigating strength of concrete built in structure. A lack on relevant data for non-destructive testing of HSC in technical and normative rules is to be considered as a significant deficiency. Evident for HSC generally is the lack in literature on deeper analysis of the factors affecting their non-destructive testing, as well a meaningful methodology or practically usable calibration relationships. HSC differs from ordinary concrete not only by used components, but also by more compact structure with different strength – elastic characteristics. Considering these differences, HSC strength prediction can not be performed by using calibration relationships developed for ordinary concrete. Moreover, the question is to what extent the current knowledge of the NDT results influencing factors can be considered as valid. The paper presents findings on the effects of the key factors affecting the measurement results of Schmidt hardness method and ultrasonic pulse method, including recommendations for the practical application of these methods. The problematic of static vs. dynamic modulus of elasticity was also solved. Calibration equations for predicting the compressive strength of HSC from the non-destructive testing parameter were elaborated, showing high cohesion among variables and practically usability.

No description available.

[pt] Projetos estruturais que empregam concretos com resistências mais elevadas, ou seja, maiores que 40 MPa, nomeados Concretos de Alto Desempenho, são cada vez mais freqüentemente utilizados. Sabe-se, entretanto, que as propriedades destes concretos são diferenciadas daquelas dos concretos considerados convencionais, necessitando-se estudos que visem, principalmente, mensurar a realidade dentro dos materiais disponíveis em nosso país. Este trabalho experimental estuda as principais propriedades deste material: resistência à compressão, resistência à tração por compressão diametral, Módulo de Elasticidade e permeabilidade, através da determinação do índice de vazios. Após um estudo sobre métodos de dosagem mais utilizados e empregando-se materiais disponíveis no Rio de Janeiro, foram moldados um total de 230 corpos de prova para resistências características à compressão de 40MPa, 60 MPa, 80 MPa e 100 MPa. Foi realizado um estudo sobre compatibilidade entre superplastificante e aglomerante. Com os dados obtidos experimentalmente, foram relacionados resistências à tração por compressão diametral, módulo de elasticidade e porosidade com resistência à compressão axial. Estes resultados foram comparados com as recomendações das principais normas internacionais e com as propostas de alguns pesquisadores que foram encontradas na literatura. / [en] High Performance Concrete, i.e., those whose compressive strength is higher than 40 Mpa, have been used in a wide range of Civil Engineering applications. Notwithstanding that, it is known that their mechanical and physical properties are different from those of their conventional counterparts. In this dissertation, it is studied mixture proportion methods with good acceptance rate, preparing 230 specimens with materials available in Brazil s state of Rio de Janeiro and that have compressive strength of 40 MPa, 60MPa, 80 MPa and 100 MPa. For each prepared specimen, it is studied its mechanical properties, compressive strength, splitting tensile strength, modulus of elasticity and porosity for the determination of the emptiness ratio. It is also studied the compatibility between superplasticizer and cement materials. It is also performed a comparison between the experimental data and the expressions available in the literature, as well as the relation between the compressive strength, splitting tensile strength, modulus of elasticity and the porosity.