The main structural objectives in column design are strength and ductility. For higher strength concretes these design objectives are offset by generally poor concrete ductility and early spalling of the concrete cover. When fibres are added to the concrete the post peak characteristics are enhanced, both in tension and in compression. Most of the available experimental data, on fibre reinforced concrete and fibre reinforced high strength concrete columns, suggest that an improvement in both ductility and load carrying capacity due to the inclusion of the fibres. In this thesis the ductility and strength of fibre reinforced high strength concrete are investigated to evaluate the effect of the different parameters on the performance of columns. The investigation includes both experimental and the numerical approaches with 56 high strength fibre reinforced concrete columns being tested. The concrete strength ranged between 80 and 100 MPa and the columns were reinforced with 1, 2 or 2.6 percent, by weight, of end hooked steel fibres. The effect of corrugated Polypropylene fibres on the column performance was also examined. No early spalling of the cover was observed in any of the steel fibre reinforced column tested in this study. A numerical model was developed for analysis of fibre and non-fibre reinforced eccentrically loaded columns. The column is modelled as finite layers of reinforced concrete. Two types of layers are used, one to represent the hinged zone and the second the unloading portion of the column. As the concrete in the hinged layers goes beyond the peak for the stress verus strain in the concrete the section will continue to deform leading to a localised region within a column. The numerical model is compared with the test data and generally shows good correlation. Using the developed model, the parameters that affect ductility in fibre-reinforced high strength concrete columns are investigated and evaluated. A design model relating column ductility with confining pressure is proposed that includes the effects of the longitudinal reinforcement ratio, the loading eccentricity and the fibre properties and content and design recommendations are given.

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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.

Thesis (Ph. D.)--University of New South Wales, 2005. / Also available online.

Thesis (Ph. D.) -- University of Western Sydney, Hawkesbury, 2000. / Includes bibliographical references (leaves 225-241).

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Thesis (M.S.)--Brigham Young University. Dept. of Civil and Environmental Engineering, 2005. / Includes bibliographical references (p. 101-102).

Thesis (M.S.)--Brigham Young University. Dept. of Civil and Environmental Engineering, 2006. / Includes bibliographical references (p. 121-122).