Browsing by Author "Mercer, Colin Douglas"

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    An analytical model for the seismic analysis of reinforced concrete frame structures
    (1988) Mercer, Colin Douglas; Martin, JB
    The thesis is concerned with developing an analytical model to describe the cyclic behaviour of reinforced concrete members. The mechanisms which are important in the behaviour of members dominated by flexural deformations are identified. They include bar-slippage due to deterioration of the bond between the steel and concrete, the crack opening and closing criterion, and the cyclic response of steel and concrete. All these mechanisms are incorporated in an analytical model based on a layered beam approach. The model is developed for a member in double curvature bending and consists of two inelastic zones on either side of a central elastic zone. The bar-slippage which occurs in the beam-column joint is included at the ends of the beam model. A linear bending moment distribution is assumed along the beam. The moment-curvature relationship is calculated in the inelastic zones; the curvature is then integrated along the inelastic zone to determine the displacements. Damage measures with an objective of predicting the onset of failure are also proposed. The implementation of the model into a frame analysis computer program is discussed. Special attention is devoted to the solution strategies and numerical algorithms employed in the computer program. The model is shown to perform satisfactorily when compared to experimental results. A simplified analytical model which approximates the concrete with only two layers is also presented. The simplified model is shown to predict the response as competently as a model with far more concrete layers; however, the computational time for the simplified model is significantly less.
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    Numerical investigation of the edge profile in hot-rolling
    (1992) Veale, John; Mercer, Colin Douglas; Martin, J B
    During the hot-rolling of aluminium ingot into sheet, the material elongates in the rolling direction as it is reduced vertically. The spread which occurs in the lateral direction during the multiple pass schedules used in industry is minimal. However, the deformation on these edges is important. During the initial passes a concave profile develops - the material near the surfaces spreads outward while the material at the centre moves inward. The concave profile can lead to defects in the final product; these are the 'roll over' of material from the edges to the top and bottom surfaces, the fold over of material in the centre of the edge, and the formation of vertical edge cracks. To remove these the edges are trimmed at the end of the process. Research work in this area was motivated by the possibility of identifying means of reducing the amount of material that needs to be trimmed. The objectives of this thesis are to develop techniques of simulating the rolling, and to use these to investigate the deformation mechanisms which lead to the concave edge profile. Models of the rolling were developed using the general purpose, non-linear finite element code ABAQUS. To reproduce the edge profiles accurately requires large three-dimensional models, for which the explicit dynamic method was found to be the most suitable. The results of the analyses were used to investigate the mechanisms which lead to the concave edge profile. In the roll-gap the work-load arches through the ingot; and for roll passes with small reductions a stress pattern occurs which leads to the concave edge profile. In this pattern the stresses of highest magnitude at the surfaces are compressive stresses in the vertical direction, while in the centre of the ingot they are orientated in the rolling direction and are tensile. Thus deformation occurs by vertical compression near the surfaces, and by stretching in the rolling direction at the centre. At the edges the material is not constrained laterally; and due to the Poisson effect, the material spreads outward near the surfaces, and moves inward at the centre. The effect of certain variables on the edge profile were investigated with the modelling. The friction between the work-rolls and the ingot was found to have significant influence on the amount of lateral surface spread. Work hardening, strain rate and temperature effects in the material lead to variations in the yield stress through the height of the ingot. These effects were included in the modelling and were found to affect the shape of the profile, but to a lesser extent than the friction.