This thesis has discussed both properties and geometry of concrete slabs used in bridges. It gave understanding on behavior of concrete in both tension and compression zones and how crack propagates in specimens by presenting both theory of fracture and performing concrete tests like tension splitting, uniaxial compression and uniaxial tension tests. Furthermore, it supported experimental tests with finite elements modelling for each test, and illustrated both boundary conditions and loads. The thesis has used ARAMIS cameras to observe crack propagations in all experimental tests, and its first study at LNU that emphasized on Brazilian test, because of importance of this test to describe both crushing and cracking behavior of concrete under loading. It’s an excellent opportunity to understand how concrete and steel behave individually and in combination with each other, and to understand fracture process zone, and this has been discussed in theory chapter. The geometry change that could affect stresses distributions has also described in literature and modelled to give good idea on how to model slabs in different angles in the methodology chapter. Thus, thesis will use finite elements program (Abaqus) to model both experimental specimens and concrete slabs without reinforcement to emphasize on concrete behavior and skewness effect. This means studying both properties of concrete and geometry of concrete slabs. This thesis has expanded experimental tests and chose bridges as an application.

La tesis se enmarca en la caracterización, a nivel material, de la fractura del hormigón reforzado con fibras de acero (SFRC) bajo solicitaciones de tracción y cortante, y sobre la determinación de parámetros que representan la tenacidad del material sometido a esos dos modos de carga. Asimismo, se han realizado ensayos hasta rotura por cortante de elementos estructurales a escala real, los cuales se han analizado utilizando formulaciones existentes en distintos códigos de diseño.El comportamiento a tracción uniaxial del hormigón reforzado con fibras de acero se caracteriza utilizando cilindros entallados, elaborados con hormigones de resistencia normal y alta, con y sin fibras de acero. La metodología se extiende también para testigos extraídos de elementos de mayor tamaño. Los resultados se utilizan para definir parámetros de tenacidad y resistencia equivalentes de post-pico utilizables para representar el comportamiento del material y para un posible diseño estructural. Además, se desarrolla un estudio paramétrico experimental, que considera diferentes variables del ensayo y forma de probetas, para definir una configuración confiable del ensayo. Se analizan los modos de rotura observados y se evalúa la respuesta tensión-ancho de fisura. Asimismo, se propone una relación tensión-apertura de fisura característica para el diseño y análisis estructural. El comportamiento a tracción uniaxial se compara también con el de flexión y tracción por compresión diametral.La fractura por cortante se estudia a nivel material, en hormigones de resistencia normal y alta, con y sin fibras de acero, utilizando la configuración de cortante directo denominada push-off. Se analizan el modo de rotura y la respuesta tensión-desplazamiento. Además, se definen parámetros basados en la tenacidad y tensiones equivalentes de cortante para una posible utilización en el diseño estructural.Con el fin de obtener resultados que validen la utilización de las fibras de acero como refuerzo de cortante y al mismo tiempo estudiar la fractura por cortante a nivel estructural, se han realizado ensayos a escala real sobre vigas de sección rectangular y en T. Se analizan las respuestas carga-flecha y carga-ancho de fisura de vigas rectangulares de hormigón reforzado con fibras de acero variando su altura y de vigas T variando las dimensiones del ala. Los resultados obtenidos experimentalmente se utilizan para verificar la aplicabilidad de los métodos de diseño existentes en el caso del hormigón reforzado con fibras de acero. Además, se presenta una propuesta para el diseño a cortante basada en la respuesta tensión-desplazamiento relativo obtenida a partir del ensayo push-off de cortante directo. / The thesis deals with the characterization of the failure of steel fiber reinforced concrete (SFRC) in tension and shear, on the material level, and the determination of parameters that represent the toughness in these two modes of failure. Tests have been performed on large-scale beams failing under shear failure, which have been analyzed using existing design code formulas. The toughness parameters determined from the material are used in the design against such failure.The uniaxial tensile behavior of SFRC is characterized using notched cylinders of normal and high strength concretes, with and without steel fibers. The methodology is also extended to cores extracted from large elements. Results are used to define toughness parameters and equivalent post-peak strengths to be used for representing the material behavior and for possible structural design. Furthermore, a parametric study considering different test variables and specimen shape is carried out in order to define a reliable test configuration. The observed modes of failure are analyzed and the stress-crack width response is evaluated. Also, a characteristic stress-crack width response is proposed for structural analysis and design. The uniaxial tension behavior is also compared with that of flexural and splitting-tension.The shear failure is studied using the direct shear push-off test configuration, in normal and high strength concretes with and without steel fibers. The mode of failure and the stress-slip and stress-crack opening responses are analyzed. Toughness parameters and equivalent shear strengths based on the test results are defined for structural design.In order to provide results for validating the use of steel fibers as shear reinforcement and for studying shear failure at the structural level, full-scale tests on rectangular and T-beams were performed. The load-deflection and load-crack width responses are analyzed and compared with results of plain concrete beam tests. The experimentally-obtained results are used to evaluate the applicability of existing design methods for steel fiber reinforced concrete. Furthermore, a proposal for shear design based on the shear stress versus slip relationship from the push-off shear test is presented.

Space structures are inevitable while covering large spans. Space structures are skeletal structures, which are lighter for the same stiffness when compared with RCC roofs. Till now, space structures, like any other metal structures have been designed assuming the joints as rigid, although there have been several publications about semi rigid joints. Of course, the publications mostly deal with 2D structures and there are very few reports on 3D structures. Space structures, by their nature fall into the latter category. The joints in a space structure are popularly called as "nodes". Generally, nodes, which ensure concentricity of member axes, are either solid or hollow. These are either cast or forged. There are other proprietary types, which do not come under the above classification, and have not been considered in this thesis. Hollow nodes are obviously more economical than solid nodes, but also more flexible. While it is prudent to prefer hollow nodes, it is equally necessary to assess their flexibility, because of its influence on the behaviour of the structure. The hollow spherical node is very popular because of its simplicity and adaptability to various forms of space frames. Double layer grids, which are the most popular forms for roofing applications, are being increasingly implemented. While the hollow spherical node is well suited for double layer grids, an evolutionary development has been what is called as the hollow octahedral node (this node is simply referred to as the 'Octa ' node in this thesis). Chapter 1 introduces space frames and double layer grids in particular, with the advantages of using double-layer grids. Jointing systems available around the world are briefed and the node connector used in the present study is introduced with a brief write-up on its advantages and disadvantages. This chapter also explores the available literature and, the scope and objectives of the thesis are mentioned. Chapter 2 introduces 3D finite element models of the hollow spherical and octahedral nodes. The stiffness matrixes of these nodes have been derived by conducting analyses on the computer for six sizes each of the Octa and spherical nodes. Using the stiffness matrix of the node, a new method of incorporating this into the regular analysis of a space truss has been developed. The new method proposed yields realistic values for the forces in the members and takes into account the elastic deflections in the node under the action of member forces. Implementation of the proposed method has been carried out by writing a custom program using state-of-the-art object oriented programming techniques. A sample problem has been analyzed using this program to demonstrate the effect of including joint flexibility. The effect of flexibility of nodes on the effective length of compression members in double-layer grids has been evaluated. The effect of compliance on the dynamic characteristics of a space frame has also been evaluated for the sample space frame with flexible joints. The analysis program has been modified to evaluate the natural frequencies of the system using rigid or flexible nodes. The study of the Octanode and spherical node under the action of uniaxial compression and tension dominates the contents of Chapter 3. The two types of nodes have been analyzed using commercially available finite element software considering material nonlinearity. The stress patterns from the analyses have been examined thoroughly. Two consistent methods for fixing the load at yield in both uniaxial compression and tension have been proposed using the load-displacement curve. Yield loads for all the nodes have been evaluated using both the methods and the results agree well between the two methods. Three material yield values have been selected for each of the node size for evaluating the yield values viz. 240,320 and 415 MPa. The members of a double layer grid are connected to the nodes by bolts and holes are drilled in the nodes for this purpose. The bolthole patterns differ between two popular types of double-layer grids. Both these bolthole patterns have been modeled separately in the above exercise and the results for these two have been shown to be approximately the same. The effect of varying diameters of the boltholes on the response of the nodes has been examined. Relationships between the yield load, diameter, thickness and material yield have been developed using the method of least squares. The differences in the behaviour of the nodes under uniaxial compression and tension have been discussed. Ramberg Osgood type of relationships have been worked out for all the load-displacement curves obtained from the analyses. The simulation of non-linear behaviour of nodes with cracks with plastic crack closing forces have been carried out with useful insights into the behaviour of the two types of nodes in uniaxial compression and tension. Chapter 4 is devoted largely for studying the two types of nodes under the influence of biaxial load combinations. The combinations studied are dual compression, dual tension and compression-tension. In all cases equal loads are applied along two orthogonal; directions in the horizontal plane. Stress patterns have been examined for each type of load combination and yield values for each case have been obtained using one of the methods proposed in chapter 3. These have been compared with the corresponding uniaxial values in both compression and tension. Some useful inferences have been possible by studying the behaviour of the nodes under the various biaxial load combinations. In each case, relationships between the biaxial yield load, uniaxial yield load, diameter of node, thickness of node and material yield of node have been obtained using the method of least squares. The nodes have been analyzed under some selected Multi-axial loading and combinations of load which cause yield based on the second method proposed in Chapter 3 have been obtained and tabulated. However, a proper and thorough study of the nodes under multi-axial loading proved to be beyond the scope of this thesis. Chapter 5 contains the contributions made towards developing new methods and algorithms for obtaining the several results of chapters 2, 3 and 4, using object oriented programming (OOP) techniques. The contributions have been in Object Pascal, the underlying language of Delphi, a popular RAD tool developed by Borland/Inprise of USA. Several new modules have been developed to reliably handle the large amounts of data generated by the hundreds of analyses detailed in chapters 2,3 and 4. The ease with which new methods were possible to be incorporated into existing software using OOP has been demonstrated, with source code examples. Comparisons with other types of tools available and die advantages of using OOP have also been demonstrated using the experience during the preparation of this thesis. A strong case for OOP as an indispensable tool for the researcher has been made. Chapter 6: Several important conclusions and suggestions for future work have been made. Appendix 1 contains a brief note on the Method of Least Squares. Appendix 2 contains a small write-up on Delphi and OOP. Concepts of OOP have been briefly described and comparisons between three popular OOP languages have been attempted. A brief description of the features in Delphi's Object Pascal has also been provided. Appendix 3 contains the listing of Unit Arrays, which is a general purpose unit developed to make handling of large arrays easy. Several matrix calculations have been implemented which make the unit extremely useful for programmers. Appendix 4 contains the full listing of program FormK, which has been developed for chapter 2 to derive the fall stiffness matrix of a space frame node. The program picks up results from several analyses, forms a few columns of the stiffness matrix and then fills up the rest using the cyclic symmetry present in the space frame node. This program is given in full, with the intention that other researchers may find it useful to use it as-is or use after making small alterations to suit their circumstances. OOP is known for fast, reliable and easy ways of implementing modifications to existing code. Appendix 5 provides the full listing of the Object Pascal program for extracting Eigenvalues of a space truss with rigid joints or flexible joints. The incorporation of flexibility of the joints proposed in chapter 2 has been implemented. Descriptions of the program's implementations have been provided in chapter 5. Bibliography contains the alphabetical list of references.