Browsing by Subject "Civil engineering"

Now showing 1 - 14 of 14
  • Thumbnail Image
    Item
    Open Access
  • Thumbnail Image
    Item
    Open Access
    A programming approach to the numerical analysis of elasto-plastic continua
    (1978) Dittmer, Colin Thomas; Martin, J B
    The application of a kinematic minimum principle involving a continuous functional subject to inequality constraints is described for the incremental analysis of elasto-plastic continua. A simple algorithm is used for solution of the resulting mathematical programming problem. The formulation is presented for problems in plane stress, plane strain or axial symmetry, using triangular constant strain finite elements, and is extended to the use of cubic quadrilateral isoparametric elements for which a numerical integration technique is employed to account for elasto-plastic interfaces within elements. The material is assumed to obey the von Mises yield condition, and be either elastic-perfectly plastic or linear kinematic hardening. Computational details and solution techniques are described, and numerical examples compared with experimental and numerical results in the literature. Some assessment is made of the relative computational efficiency of the method.
  • Thumbnail Image
    Item
    Open Access
    Behaviour of reinforced concrete deep beams
    (1985) Green, Jeremy Robert; Green, Jeremy Robert; De Kock, M O
    Twenty five model beams were progressively loaded to failure in order to investigate the influence of the following variables on the behaviour of reinforced concrete deep beams : i) Concrete compressive strength ii) Reinforcement iii) Geometry. The model beams were all of 1500mm span, with a depth of 750mm. This span to depth ratio of 2 corresponds to the upper limit, to which the recommendations for deep beam design applies, as provided by many current codes of practice. Methods currently in use for the design of reinforced concrete deep beams were reviewed and compared. The experimental results were compared with the predictions of these design methods. This comparison revealed a large lack of agreement in the predictions of the cracking and ultimate strengths of deep beams.
  • Thumbnail Image
    Item
    Open Access
    Biological nitrogen and phosphorus removal on large plants.
    (1983) Nicholls, Harold Arthur; Marais, Gerrit van Rooyen
    Full scale implementation of biological excess phosphorus removal by means of the activated sludge process commenced in South Africa at the Johannesburg Alexandra Plant in 1974. Originally the plant was designed to operate in the nitrifying extended aeration mode; but by switching off some surface aerators around the common inlet point for the influent and underflow recycle, an anoxic zone was created to induce denitrification. This operational modification worked very successfully. Later additional aerators were switched off to create an anaerobic-anoxic zone at the head of the aeration basin, in this manner attempting to induce the prerequisite conditions for excess biological uptake of phosphorus as put forward by Barnard (i.e. by stimulating P release under anaerobic conditions). This revised operational procedure was not successful due to difficulties experienced in controlling mixing in the anaerobic - anoxic zone. However the experience gained from this investigation together with research findings at laboratory and pilot scale level at the National Institute for Water Research, the University of Cape Town, and Johannesburg instilled sufficient confidence into City Council staff to proceed with the' design of the 150 Ml/d Goudkoppie Plant, initially for nitrogen removal and to subsequently modify it to a 5 stage Phoredox process for both nitrogen and phosphorus removal. Before the plant was commissioned (1976) it was necessary to proceed with extensions to the Northern Works and these were also based on the 5 stage Phoredox process. All the Johannesburg activated sludge plants were comprehensively monitored to determine their performance under cyclic flow and load conditions, The data collected from the Goudkoppie plant were particularly comprehensive and exhaustive. Concomitant with the monitoring program extensive research into the single stage nitrification/denitrification/excess phosphorus removal process was being undertaken by the three agencies mentioned earlier. Of particular interest was the development by the University of Cape Town of a general kinetic model of the single sludge activated sludge process that described carbonaceous degradation, nitrification and denitrification behaviour under cyclic flow and load conditions. This dissertation critically evaluates the predictions of this model against the observed responses on the Goudkoppie and Northern Works.
  • Thumbnail Image
    Item
    Open Access
    Calibration of an arch dam model by the finite element method using ambient vibration testing
    (2012) Makha, Ramonate; Moyo, Pilate; Beushausen, Hans-Dieter
    The finite element model of an arch dam was calibrated for dynamic behaviour using the measured natural frequencies and mode shapes as benchmarks. The properties were extracted from the structure using ambient vibration testing techniques. Besides the geometry and general material properties of the dam wall concrete and foundation rock, the measured frequencies and mode shapes depend on the conditions at the dam site namely water level, temperature and the interactions between the several components of the dam. This study, however investigated the effects of the water level and to some extent, the effect of dissimilar foundation abutment material properties on the natural frequencies of the dam. A dam is continuously in harmonic motion due to some environmental factors such as wind. Either due to this movement of the dam itself or the internal movement of the reservoir water, a dynamic interaction occurs between the water and the dam wall where the movement of the one medium affects the other. A study conducted in the early twentieth century deduced that it is only part of the reservoir water that can be assumed to interact with the dam. It is from the same study that the Westergaard added mass concept was born which says that the interacting water mass can simply be added to the dam wall mass, a procedure from which the extraction of the dynamic properties can ensue as normal. This added mass formulation was derived on a basis of some assumptions which include a rigid and vertical dam wall and the incompressible water body. The added mass concept was extended to account for flexibility and curvature of the upstream dam wall in more recent studies. The extended version of the Westergaard method is normally referred to as the generalized Westergaard method. The original Westergaard added mass formulation was used to account for the dam wall- water interaction in the double curved Roode Elsberg dam model. This proved to be problematic as this dam is highly asymmetrical and has diverging reservoir walls, the characteristics of which are not catered for in the original Westergaard added mass method. The combined effect of using the original Westergaard method and these deficiencies in the formulation resulted in the model's natural frequencies being lower than the field ones, for the same ambient conditions. On the basis of literature, a factor of 0.8 on the added masses was applied on all the original Westergaard added masses to account for the effect of the diverging reservoir walls. The remaining masses were then reduced until a good correlation of the field frequencies and model frequencies was achieved. This was done to account for the effects of the flexibility of the dam and the curved upstream dam wall. All in all, a factor of 0.25 on the masses calculated using the original Westergaard added masses was applied to account for all the above-mentioned effects. This factor compares favourably with literature even though in literature it is rarely mentioned what effects are being accounted for when this factor is introduced. This work hence raises awareness about the shortcomings of the Westergaard method when used for model calibration and how those shortcomings can be accounted for. In summary, these shortcomings are brought about by assuming a prismatic and infinite reservoir, while in reality this is not always the case. It appears that these shortcomings affect the results of the added mass approach when used as a tool to represent the dam-water dynamic interaction in arch dams.
  • Thumbnail Image
    Item
    Open Access
    Design and control of equalization tanks.
    (1982) Dold, Peter Lorimer; Marais, Gerrit van Rooyen
    The objective of this investigation was to develop a control strategy for the operation of an equalization tank upstream of a waste water treatment plant which utilizes the available equalization hold-up volume in such a manner that it reduces, optimally, diurnal fluctuations in both influent flow and load rates. The influent to a wastewater treatment plant generally exhibits wide diurnal variations in both flow rate and concentration, and consequently in load rate (defined as the product of flow rate and concentration). Deviations of these parameters from steady state cause plant operating problems in areas such as aeration control (due to load rate fluctuations) settling tank overloading due to flow rate fluctuations) and/or over- or under-aeration which affects settling properties, and others.
  • Thumbnail Image
    Item
    Open Access
    The free basic water policy of South Africa : an evaluation of its implementation
    (2014) Farrar, Lauren Judy; Rivett, Ulrike
    South Africa is still feeling the effects of the forced inequalities the apartheid system introduced and the resulting wide-spread poverty. Inequalities are particularly evident in the quality of services provided to different areas, which are in the majority still defined by race. The majority of White households have very good service provision, with water piped directly into the home. A great number of Black and Coloured households, by contrast, have very low levels of service where family members have to walk to collect water from communal taps. To this day, there are households in South Africa that do not have access to water infrastructure at all relying on rivers, streams or boreholes, with an increased risk of experiencing water borne diseases. With the end of apartheid and the beginning of democracy in 1994, the new government prioritised the redress of inequalities and sought to better the lives of the poor by providing them with improved services. This meant building or upgrading infrastructure as well as ongoing maintenance; whilst the initial costs were high, it became very quickly apparent that revenue needed to be collected in order to cover costs. Between 2008 and 2009, 26.3% of South Africans were living below the food poverty line of R305 per person, and 52.3% were living below the upper bound poverty line, and this meant that many households were not able to afford the upgraded services. In recognising this challenge the Free Basic Water Policy (FBWP) was established in 2001, which provided a limited “lifeline” supply of water to every household for free, while any additional water usage would have to be paid for. When the FBWP was conceptualised, it was designed to meet certain implementation and supply quality goals and standards. However, over time criticism rose that these goals had not been achieved and that in some cases the policy proved counterproductive. The objective of this dissertation is to examine the implementation of FBWP thus far, and to assess whether or not it is achieving the originally intended goals and standards. Quantitative data was gathered and used to compare the progress of the implementation of the FBWP to the implementation goals in order to assess whether or not the goals are being met. Overall there were six major goals for the implementation of the FBWP, with specific targets and standards pertaining to each goal. For the purpose of this study, the data for each goal was analysed and discussed so that the progress in achieving each goal could be assessed. The findings show that significant progress and improvement has been made in supplying Free Basic Water (FBW]. Although access to water supply and FBW, the level of service provided and the quality of the water have improved, there are still households who are not receiving FBW at the required standards. From the rate of progress made it can be seen that the original intention of providing FBW for all by 2014 was over-optimistic. A second finding was that the FBWP is not financially sustainable at present and that there is currently a lack of asset management and maintenance planning in many municipalities in South Africa, which has resulted in substantial revenue losses. It was also found that the monitoring of the FBWP is currently not sufficient. Aspects such as appropriateness of the allocated amount can only be resolved with improved monitoring mechanisms. The effectiveness of education programmes on water usage requires assessment in order to understand how increased awareness can impact on households’ ability to safe water.
  • Thumbnail Image
    Item
    Open Access
    Limit Analysis and Shakedown in Plane Frames and Plane Stress Problems
    (1977) Douglas, Andrew Sholto; Martin, JB
    A method is developed for the determination of the shakedown load factor for elastic, perfectly plastic plane frames subjected to cyclic loading or random loads varying between fixed limits. The essential feature of the method is the employment of an automatic force method of elastic analysis which provides self-stress systems for the frame. This in turn permits the ready formulation of the compatibility requirements which are imposed on plastic hinge rotations. As a result, the analysis proceeds with data input which is comparable to straightforward kinematic analysis. A preliminary study of the generalisation of this approach to the limit analysis of plane stress problems is also given.
  • Thumbnail Image
    Item
    Open Access
    Plastic buckling of initially imperfect stiffened cylinders in axial compression
    (1981) Duffett, Gino Alan; Reddy, B Daya
    Bifurcation in the plastic range of axially compressed stringer-stiffened cylinders is investigated. The shell under consideration is assumed to have an initial imperfection in the form of a sinusoidal deviation both axially and circumferentially.The constitutive relation employed here is J 2 deformation theory of plasticity. This relation, as well as kinematic assumptions regarding the behaviour of the panels and stiffeners which constitute the stiffened shell is used in the principle of virtual work to obtain a set of non-linear algebraic equations whose solution provides complete information about the prebuckling equilibrium path. Bifurcation from the primary path is examined by making use of a functional whose first variation is zero when two solutions to the problem are possible. This leads to an eigenvalue problem, the eigenvalue being the critical compressive load and the eigenfunction being the corresponding buckling mode. Results are presented or shells of different geometries and material properties, a limited comparison of theoretical results as obtained by this analysis with available experimental data is also made.
  • Thumbnail Image
    Item
    Open Access
    A programming approach to the numerical analysis of elasto-plastic continua
    (1978) Dittmer, Colin Thomas; Martin, J B
    The application of a kinematic minimum principle involving a continuous functional subject to inequality constraints is described for the incremental analysis of elasto-plastic continua. A simple algorithm is used for solution of the resulting mathematical programming problem. The formulation is presented for problems in plane stress, plane strain or axial symmetry, using triangular constant strain finite elements, and is extended to the use of cubic quadrilateral isoparametric elements for which a numerical integration technique is employed to account for elasto-plastic interfaces within elements. The material is assumed to obey the von Mises yield condition, and be either elastic-perfectly plastic or linear kinematic hardening. Computational details and solution techniques are described, and numerical examples compared with experimental and numerical results in the literature. Some assessment is made of the relative computational efficiency of the method.
  • Thumbnail Image
    Item
    Open Access
    Seismic analysis of pipelines with yielding supports
    (1984) Ibell, Christopher Anthony; Martin, JB
    Pipelines in structures such as a nuclear reactor can be analysed separately when the structure is subjected to seismic type loading. The pipeline is modelled with various types of supports, such as a rigid support or an elastic support. The pipeline is analysed and designed so that stresses in the pipeline and at the supports are acceptable. When the pipeline is subjected to a larger intensity earthquake than that designed for, the stresses at some supports may exceed the yield stresses, causing the support to yield. The yielding of a support can influence the response at the other supports in the pipeline, and in some cases cause failure of the supports to occur. This thesis investigates the effect yielding of an internal pipe hangar support in a two-span pipeline has on the adjacent end supports. Essentially the findings are that the yielding of the pipe hangar support is not detrimental to the overall stability of the pipeline, as long as the support does not yield excessively.
  • Thumbnail Image
    Item
    Open Access
    The analysis of rigid-viscoplastic plane structures subjected to large impulsive loading
    (1982) Griffin, Paul Dominic
    This thesis is concerned with the analysis of plane ductile beams and frames which are subjected to large impulsive loading. The elastic response is ignored, and the material is considered as rigidviscoplastic in order to take rate effects into account. Computational advantage is obtained by modelling this behaviour by a homogeneous viscous constitutive relation, as the rigid phase is absent. As opposed to the standard displacement method finite element formulation where interpolation functions describing the velocity field across elements are given, a formulation is used in which nodal velocities, moments and element axial forces are carried as parameters. Three methods of analysis are presented; firstly, the mode approximation technique is described, where the actual behaviour of the structure is approximated in closed form by the product of a mode shape and a function of time. A new algorithm for the determination of the mode shape is presented. The mode technique is then extended to include geometric effects by means of the instantaneous mode solution technique. Secondly, a method is given whereby at each instant the accelerations (by the Tamuzh principle) and the rates of change of moment (by virtual velocities formulation) are found, and velocities and moments are integrated forward independently to obtain a solution. Finally, a direct method of analysis is described, where nodal forces conjugate to a given velocity field are calculated (by the principle of virtual velocities), and hence from the equations of motion, accelerations are determined. An implicit forward integration scheme is employed to advance the solution in time. Illustrative examples are presented which show that these techniques give very good and computationally efficient predictions of the displaced shape of the structures under consideration, even when displacements are in the order of the dimensions of the structure.
  • Thumbnail Image
    Item
    Open Access
    The influence of various South African aggregates on the creep of concrete
    (1985) Mallows, Frank Arthur
    The aim of this thesis is to identify which south African aggregates have an extreme effect on the creep of concrete. Eight sets of experimental data, incorporating five types of aggregate, are presented. Further secondary effects have also been identified from the experimental results. These include Admixtures, Eastern Province Cement and Heat-curing. A computer program, CONVERS3, was developed in order to convert experimental results from the form of specific creep to that of creep factor, thereby making the data more accessible for comparison purposes. In order to allow for variation in cement content and age of loading, between the different test series, the partial coefficients from the CEB 1970 code recommendations were incorporated in the program. Once these variations had been allowed for, the results from the various test series were then compared in order to identify the secondary effects of Aggregate Type, Admixture, Cement Type and Heat-curing. The comparison of the test data is presented in two forms, namely, creep factor against time plots, and 300-day creep factor values. The latter were obtained by fitting a hyperbolic curve to the experimental data and thereby interpolating a value at 300 days. By comparing the experimental data, it was found that the use of an Eastern Province Ordinary Portland Cement, and the use of a P4 Admixture, both caused a 25% increase in the resulting creep factor. From the aggregates decreasing sandstone, comparisons that were made, it was found that the affected the creep of concrete in the following order of influence: Eastern Province Quartzitic Reef Quartzite, Hornfels, Granite and Dolerite.
  • Thumbnail Image
    Item
    Open Access
    The use of a non-classical friction law in finite-element analysis of contact problems
    (1983) Bolt, Andrew Clifford; Reddy, B Daya
    In this thesis a description is given of the numerical treatment of contact problems in elasticity. Frictional effects on the contact surface are modelled by using a nonlocal, nonlinear friction law. Features of the boundary value problem, which merit special attention, are the presence of inequality constraints and the fact that the contact surface is not known a priori. Finite element approximations based on a variational formulation of the problem, developed by Oden and Pires, are used to generate a discretised version. The solution procedure incorporates an iterative algorithm for the determination of the extent of the contact surface. Alternative techniques for the evaluation of the frictional stresses on the contact surface are described and numerical examples are presented.