Dissertations / Theses on the topic 'Columns, Concrete Testing Mathematical models'

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>A evolução dos concretos utilizados nas últimas décadas deu origem ao Concreto de Alto Desempenho (CAD), que tem, entre suas características, alta resistência à compressão e baixa permeabilidade. Com o desenvolvimento dos produtos químicos utilizados na construção civil, em especial os superplastificantes e superfluidificantes, a utilização desse tipo de concreto tornou-se cada vez mais freqüente pela possibilidade de se obter uma mistura suficientemente trabalhável utilizando-se fatores água/cimento menores do que 0,35. Devido à sua microestrutura mais homogênea, esse tipo de concreto apresenta um comportamento mais frágil do que os concretos convencionais, exigindo uma melhor caracterização do material. A partir do final da década de 70 começou-se a aplicar os conceitos da Mecânica da Fratura para análise do comportamento de estruturas construídas com esse tipo de concreto. Como em algumas situações a resistência nominal de peças de concreto diminui com o aumento de suas dimensões, houve a necessidade de se considerar o efeito de escala das estruturas a fim de se obter níveis de segurança mais adequados no seu dimensionamento, o que justificou a utilização da Mecânica da Fratura. Neste trabalho a energia de fraturamento foi obtida experimentalmente pelo método do trabalho de fraturamento e pelo método do efeito de escala, por meio de ensaios estáveis de flexão de três pontos em amostras de concreto de alto desempenho com entalhe. Foi também desenvolvida a simulação numérica de uma viga com entalhe, analisada pelo método dos elementos finitos e empregando-se na modelagem constitutiva os conceitos da Mecânica da Fratura aplicada ao concreto. As vigas foram moldadas e ensaiadas no Instituto Politécnico do Rio de Janeiro (IPRJ) da Universidade do Estado do Rio de Janeiro (UERJ) na cidade de Nova Friburgo. Os ensaios foram realizados com controle de deslocamento da célula de carga. Foram ensaiadas três séries de 12 vigas, com quatro dimensões diferentes, geometricamente proporcionais, e três amostras para cada dimensão, totalizando 36 vigas. As alturas utilizadas para as vigas foram 38, 76, 152 e 304 mm, e sua espessura foi mantida constante igual a 38 mm. Os corpos de prova cilíndricos, para caracterização da resistência à compressão do concreto, foram moldados no IPRJ e rompidos no laboratório de engenharia civil da UERJ, na cidade do Rio de Janeiro. Os concretos utilizados apresentaram resistência à compressão média de 70 MPa.<br>The evolution of the concrete mixes used during the last decades gave birth to the High Performance Concrete (HPC), which, among its main characteristics, presents high strength and low permeability. With the development of chemical products used in civil engineering constructions, mainly the superplasticizers, the use of this kind of concrete has become more and more frequent due to the possibility of obtaining a workable mixture with a water/cement ratio lower than 0.35. Due to its more homogeneous microstructure, the HPC presents a more fragile behavior than the conventional concrete, demanding a better characterization of the material. At the end of the 1970s, concepts of the Fracture Mechanics started to be used for the analysis of the structural behavior of concrete structures. As the nominal stress of the material decreases as the size of the structure increases, it became necessary to consider this size effect in the analysis in order to obtain more suitable levels of security. This fact justifies the use of the Fracture Mechanics in the structural analysis of concrete structures. In this work, the fracture energy was experimentally obtained using the work-offracture method and the size effect method by performing three-point bend tests in HPC notched beams. It was also developed a numerical simulation of the tests, performing the analysis through the Finite Element Method and applying the concepts of the Fracture Mechanics of Concrete into the constitutive model. The notched beams were molded and tested at the Polytechnic Institute of the State University of Rio de Janeiro (IPRJ/UERJ), located in the city of Nova Friburgo. The tests were controlled by the vertical displacement of the load cell. Three series of twelve beams with four geometrically similar sizes were tested. Three samples for each size were cast, making an amount of 36 beams. The beams were 38, 76, 152 and 304 millimeters high and the width was kept constant equal to 38 millimeters. To characterize the concrete compression strength, 100x200 millimeters cylinders were molded at the IPRJ and tested at the UERJ civil engineering laboratory in the city of Rio de Janeiro. The tested concretes presented a medium compressive strength of 70 MPa.

"June 2002"<br>Includes bibliographical references (leaves 349-374)<br>xxxix, 416 leaves : ill., plates ; 30 cm.<br>Thesis (Ph.D.)--University of Adelaide, Dept. of Civil and Environmental Engineering, 2002

This thesis investigates the behaviour of hollow and concrete filled steel columns fabricated from thin steel plates. The columns are investigated under axial, uniaxial and biaxial loading. The currently available international standards for composite structures are limited to the design of concrete filled steel columns with compact sections and yield stress of steel up to 460 N/mm2. This thesis consists of both experimental and analytical studies and design recommendations for future use. Three comprehensive series of experimental tests are conducted on hollow and concrete filled steel columns. The principal parameters that have been considered in the test programmes are the slenderness of the component plates, the yield stress of the steel and the loading conditions. In the first test series, three slender hollow steel columns and three slender composite columns are tested under uniaxial loading. The steel utilised is mild steel. High strength steel is utilised in the second test programme. In this test series four stub columns, eight short columns and eight slender columns are tested, each set consists of four hollow and four composite columns. Short columns are tested under axial loading to investigate the confinement effect provided by the steel casing. Slender columns are tested under uniaxial loading to investigate the coupled instability of local and global buckling. The third test programme is quite novel and considers the behaviour of hollow and concrete filled steel columns fabricated with high strength structural steel plate and subjected to biaxial bending. In this test eight short columns and ten slender columns each of them consisting of hollow and composite columns are investigated under biaxial loading. Analytical models are developed herein to elucidate the behaviour of the hollow and composite columns considering cross section slenderness, yield stress and loading conditions. An iterative model considering the coupled global and local buckling in the elastic and plastic range incorporating material nonlinearities is developed to investigate the behaviour of slender columns fabricated from mild steel. An improved deformation control model is developed to investigate the behaviour of slender high strength steel columns considering the confinement effect and local and post-local buckling in the elastic and plastic range. Then a numerical model for biaxial bending is developed to study the behaviour of short and slender concrete filled high strength steel columns under biaxial loading incorporating interaction buckling considering material and geometric nonlinearities. The scope of the thesis presents a wide range of experimental and theoretical studies of an extremely novel nature. It demonstrates the benefit of confinement and the consideration of local and post-local buckling in the elastic and plastic range. It is hoped that this research will contribute to the area of composite steel-concrete structural applications.

Concrete-filled double steel tubular (CFDST) columns are high-performance composite columns, which have increasingly been used in high-rise composite buildings and bridges as well as in strengthening conventional concrete-filled steel tubular (CFST) columns. The additional confinement provided by the inner circular tube in CFDST columns considerably improves their strength and ductility compared to CFST columns. However, research studies on the behavior of CFDST columns have been very limited and no design rules are given in current design codes. This thesis presents experimental and numerical studies on the fundamental behavior of circular and rectangular CFDST short and slender columns subjected to axial compression, combined axial load and bending, and preloads. Experiments on the behavior of square CFDST short columns with circular inner tube, circular CFDST short columns with circular inner tube and rectangular CFDST short columns composed of inner rectangular tube loaded concentrically and eccentrically are undertaken. Fiber-based mathematical models are developed for predicting the structural responses of CFDST short and slender columns under various loading conditions. The formulations of the mathematical models consider the influences of concrete confinement, geometric and material nonlinearities, and local buckling. New confining pressure models are proposed based on test results for ascertaining the compressive and residual strengths of confined concrete in CFDST columns, and incorporated in the mathematical models. The highly dynamic nonlinear equilibrium equations of CFDST columns under eccentric loading are solved by the efficient computer solution algorithms, which are developed based on the inverse quadratic method. The validations of the numerical models are made by comparisons with experimental results. The influences of various geometric and material parameters on the behavior of CFDST columns are examined. The results obtained from experimental and numerical studies are used to propose design equations. This research makes significant contributions to the knowledge by adding new test results on CFDST short columns to the database. The numerical models developed provide researchers and structural designers with accurate and efficient computer simulation and design tools, which lead to safer and more economical designs of composite structures. The design equations proposed can be utilized to design CFDST short and slender columns under various loading conditions.

Bibliography: leaves 140-144.<br>xix, 156 leaves : ill. ; 30 cm.<br>Title page, contents and abstract only. The complete thesis in print form is available from the University Library.<br>Determines the effect of partial-interaction and interfacial friction on the fatigue behaviour of composite bridge beams and develops a set of design rules for the assessment of the residual strength and performance of composite bridge beams.<br>Thesis (Ph.D.)--University of Adelaide, Dept. of Civil and Environmental Engineering, 1999

Bibliography: leaves 140-144.<br>xix, 156 leaves : ill. ; 30 cm.<br>Determines the effect of partial-interaction and interfacial friction on the fatigue behaviour of composite bridge beams and develops a set of design rules for the assessment of the residual strength and performance of composite bridge beams.<br>Thesis (Ph.D.)--University of Adelaide, Dept. of Civil and Environmental Engineering, 1999