Infrastructure Engineering - Theses
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ItemTransmission of high strength concrete corner column loads through normal strength concrete slabs( 2003)Reinforced concrete buildings are commonly designed to consist of high strength concrete columns and normal strength concrete slabs. The usual method of construction involves casting the columns up to the underside of the slab they will support and then casting the slab continuous through the columns. The columns of the next storey are then cast and so the process continues, resulting in a layer of slab concrete intersecting the high strength concrete columns at each floor level. The axial load on the column must therefore be transmitted through the weaker slab layer. The effect of this weaker slab layer on the overall column strength and failure characteristics is the topic of this research. Current code provisions for the prediction of the effective strength of a column intersected by a weaker slab layer are inadequate. Provisions in the American Code, ACI 318-99 can be unconservative in many cases, the Canadian Code, CSA A23.3-94 can be overly conservative in its recommendations, while the Australian Concrete Structures Code, AS3600-2001 is very limited in its applicability and can also be unsafe. This thesis presents a comprehensive review and assessment of available code provisions and other recommendations put forward by past researchers on the transmission of high strength concrete column loads through normal strength concrete slabs, covering interior, edge and corner columns. An experimental investigation on the behaviour of corner columns is presented. Five specimens were tested, all with a joint aspect ratio (h/c) equal to 0.7. Of these, three were sandwich column specimens and two were corner column specimens consisting of a slab portion extending beyond the column faces in two directions. The slabs of the corner column specimens were loaded to simulate real conditions. The experimental program was intended to investigate the influence of adding lateral reinforcement to the slab layer and the effect of the surrounding slab on a corner column. Based on past findings and the results of this investigation, an empirical design equation for the prediction of the effective strength of corner columns is proposed. Using an analogy with the behaviour of brick masonry, a theoretical basis explaining the behaviour and failure mechanism of high strength concrete corner column - normal strength concrete slab joints is established. This theory is used to derive a formula for the prediction of the effective strength of corner columns and is verified against all existing test data. The theory is also extended to predict the behaviour of edge and interior column - slab joints.
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ItemFlexural ductility of high strength concrete columns( 1995)A method for the design of reinforced high strength concrete columns considering the flexural ductile behaviour is presented in this thesis. High strength concrete, as used in this study, is defined as concrete with compressive strengths exceeding 50MPa. The study covers the following areas: A concrete stress-strain model previously used for normal strength concrete column analyses is presented along with a modification to include the characteristic behaviour of high strength concrete. The thesis also gives a literature review of the available information on the performance of high strength concrete columns. An experimental investigation of the influence of concrete strength, stirrup spacing, axial load level, and the percentage of longitudinal steel on the stress-strain and movement-curvature behaviour of confined concrete is presented. The test units included eight rectangular columns of compressive strengths ranging from 30 to 65MPa. The available strength and ductile behaviour of the columns is discussed and compared with the performance of columns tested previously at the University of Melbourne and Monash University, as well as with various analytical models, including the modified concrete stress-strain model mentioned above. A method for the determination of stirrup spacing resulting in equivalent ductile performance to that specified by the current Australian Concrete Code (AS3600) is presented. A set of criteria for the ultimate limit state including longitudinal steel buckling and lateral steel fracture was used to establish a design method for the available strength and ductility of high strength concrete columns. The effect of concrete cover on ductile behaviour is also discussed. Various spreadsheets were developed to determine such parameters as concrete strain at lateral steel fracture and strain at longitudinal steel buckling. A spreadsheet which determines the stirrup spacing of a column as specified by various codes and research reports was also developed. Two fortran computer programs which determine the axial force - moment interaction diagram and the moment-curvature curve of a reinforced concrete section were modified to include new stress-strain relationships suitable for high strength concrete and ductility measurements.