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The poor durability performance of reinforced concrete structures is a major problem facing the construction industry throughout the world. It IS estimated that more than $200 billion will be required to repair and rehabilitate deteriorated concrete structures in the USA. Similarly, it is estimated that more than £2 billion will be needed to repair deteriorated concrete structures in the UK Also, considerable resources have to be diverted towards the repair of deteriorated concrete structures in the countries along the Arabian Gulf. Concrete deterioration, worldwide, is mainly attributed to reinforcement corrosion that is caused by chloride ions. However, the effect of other ions, particularly sulfates, on reinforcement corrosion has not been adequately studied. Reinforced concrete structures in marine environments and those built in ‘sabkha' soils are exposed to both chloride and sulfate salts The combined presence of these two ions may accelerate reinforcement corrosion. Cement chemistry may also Significantly influences the mechanisms of reinforcement corrosion. The quantity of C3A and the alkali content of cement effects its chloride-binding capacity. While considerable research has been conducted on the effect of C3A content of cement on its chloride-binding and reinforcement corrosion, meagre data exist on the effect of cement alkalinity on chloride-binding, while no study has been conducted to evaluate the effect of cement alkalinity on reinforcement corrosion.

This thesis is concerned with the analysis of large offshore gravity structures used for oil exploration and recovery in the Beaufort Sea. Because of the high ice loads and the water depths involved, these structures comprise a large steel box infilled with a sand core for stability. One such structure was subjected to severe ice loading in April 1986 causing portions of the sand core to liquefy and bring the structure to a near failure condition. This structure was heavily monitored and thus serves as a case study against which the proposed analysis procedure can be checked. The behaviour of these soil-structure systems is highly complex depending upon the characteristics of the soil, the structural elements and the soil-structure interface. In this thesis a three-dimensional Finite Element computer program with soil, interface and structural elements is developed. Emphasis is placed on the three-dimensional stress-strain constitutive law both in terms of its ability to model observed laboratory response as well as the determination of the constitutive law parameters from in situ testing. The results obtained in terms of displacement, acceleration and zones of liquefaction by the analysis were then compared with the field measurements obtained during the April 1986 ice load event. The good agreement obtained between predicted and observed response is a validation of the proposed procedure. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Le développement des technologies modernes exige que l'on utilise des matériaux présentant des propriétés mécaniques élevées spécifiques à leur emploi mais dont les masses volumiques soient faibles. Les matériaux composites sont des matériaux qui répondent aux exigences précédentes. En raison de leur intérêt, les matériaux composites ont d'abord été utilisés dans nombreux secteurs d'activité (aérospatiale, automobile, construction, etc.). Dans les matériaux composites, une catégorie nous intéresse plus particulièrement de part ses possibilités de conception et de développement : les structures composites qui résultent d'une manière générale de l'assemblage d'un matériau de peau présentant une grande rigidité et d'un matériau d'âme de faible densité. Ces matériaux montrent un rapport performances mécaniques/densité très intéressant comparé à des matériaux plus classiques. Les propriétés finales de ce type de matériau sont directement dépendantes des propriétés constituantes et de la qualité de leur assemblage. Afin d'apporter des solutions aux industriels, de nombreux développements et études au cours de ces dernières années ont eu pour but l'optimisation du rapport performance mécanique/densité. Ce travail de thèse a été entrepris avec le même objectif, mais en ayant une stratégie d'optimisation se focalisant plus particulièrement sur le matériau d'âme. Notre démarche est de repenser dans son intégralité le matériau d'âme et de proposer un nouveau concept d'âme complexe qui repose sur l'empilement de matériaux de natures différentes suivant une séquence bien précise, Les résultats expérimentaux obtenus sont confrontés à une approche théorique basée sur une méthode d'éléments finis / The development of modern technologies requires that one use materials presenting high mechanical properties specific to their employment,but whose densities are low. The composite materials are materials which fulfil the preceding requirements. Because of their interest, the composite materials were initially used in aerospace, automotive, and construction industries. In composites, a class of particular interest ragarding the possibilities of design and development concern the sandwich structures resulting from a general assembly of a skin material with high stiffness and core materials of low density. The final properties of the materials are directly derived to the industry, many developments and studies in recent years have been aimed at optimizing the ratio mechanical performance over density. This thesis was undertaken with the same objective, but by having a strategy of optimization being focused more particulary on core materials. Our process is to reconsider in its entirety core materials and to propose a new concept of core complex which rests on the material stacking of different nature according to a quite precise sequence. The experimental results are correlated with those obtained by a theoretical approach based on a finite element method

The problem of the dynamics of a flexible offshore structure in either a regular or random sea is considered in this thesis. A simple single degree of freedom model of the structure is assumed and the relative velocity formulation of the Morison equation is used to describe the fluid force. The resulting equation of motion is a nonlinear ordinary differential equation with either harmonic or stochastic forcing depending on the wave description. Solutions are obtained for regular deterministic waves by numerical integration, various linearization methods and a new perturbation method developed in this thesis. The numerical solution is used to assess the accuracy of each of the approximate solution methods. Of these, the perturbation method is found to give the best approximation to the numerical solution over the complete frequency range of interest. For random seas the response spectrum and the mean square response are obtained by various linearization methods, the method of equivalent linearization, and by the new perturbation method. The perturbation method and the method of equivalent linearization are very similar in that they both yield the same values of effective damping. Comparison of the results obtained by a numerical simulation method with the results of the perturbation method and the widely used method of equivalent linearization shows that the perturbation method gives a better estimate of the response mean square value than does the method of equivalent linearization. For all of the approximate solution methods that are discussed it was found that the use of Hermite polynomials to represent the solution is very effective in obtaining various expected values required in the computational procedure. In addition to the average response statistics, such as the response mean square value, the probability density of the response is also considered. It is well known that the response of a linear system to Gaussian forcing is itself Gaussian. The wave force given by the Morison equation is non-Gaussian and therefore the response is also non-Gaussian but of unknown form. The hypothesis that for a linear equation, the probability density of the response is of the same form as the probability density of forcing, even for the case of non-Gaussian forcing, is investigated and verified using the results of numerical simulations. Design considerations of interest which follow from the response probability density are also discussed. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The objective of the work described in this thesis is to evaluate the significance of the ambient fluid on the motion of an ice mass in the vicinity of an offshore structure and during the subsequent impact mechanism. Models for iceberg drift are first reviewed. The changes in flow field around an ice mass drifting in a current near an offshore structure are investigated by potential flow theory. The proximity effects and current interactions are generalized by introducing the added mass and convective force coefficients for the ice mass. A two-dimensional numerical model based on the boundary element method is developed to calculate these coefficients over a range of separation distances up to the point of contact. A numerical model based on ice properties and geometry is developed to simulate the impact force acting on the structure. Both the 'contact-point' added masses estimated in this thesis and the traditionally assumed far-field added masses are used in the impact model separately. The results from the two cases are compared and the crucial roles played by the ambient fluid during impact are discussed. Finally, a number of related topics is proposed for further studies. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

A series of laboratory experiments was conducted to examine the oscillatory forces" and the wave runup on a vertical, circular, surface piercing, rigid cylinder in the presence of both waves and a colinear current. It was found that a current which ran opposite to the direction of wave propagation reduced the oscillatory force and the runup on the cylinder. The results for a current running in the same direction as the waves were more scattered, with some cases indicating an increase in force while others a decrease. The runup, however, increased in all cases. An innovative numerical technique which is currently under development was applied to this problem. The loads on the cylinder were obtained by a time stepping procedure in which the flow at each time step was calculated by an integral equation method based on Green's theorem. The general results of the numerical method agreed quite well with the experimental observations, within the constraints of some simplifying assumptions. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

In order to design a successful space system, the unique challenges of the space environment it will operate in must be considered during the design process. Atomic oxygen (AO) is a detrimental environmental effect found in Low Earth Orbit (LEO) that affects spacecraft surfaces by oxidizing and eroding material over time, particularly polymers. Carbon fiber/epoxy composites are a commonly used spacecraft material affected by AO exposure. Carbon composites are used as a structural material, such as on solar panels; their large surface area therefore is a potential contamination source to sensitive components. The Space Environments and Testing Lab at California Polytechnic State University, San Luis Obispo (Cal Poly SLO) includes an apparatus that can simulate AO in the LEO environment. This apparatus was used to expose carbon composite samples to AO before being tested for short beam strength to measure the effect on material properties. Results showed no significant difference in short beam strength for a 24-hour AO exposure compared to unexposed samples, but a 4% decrease for samples with a 48-hour exposure. Previous work at Cal Poly SLO found that AO-exposed composite generated particulate contaminants. Tape lift tests and mass measurements of samples were conducted before and after AO exposure to characterize the particulate contamination generated and percent mass loss. It was found that AO exposure increased the percent mass loss by 1.5% for 24-hour exposure and 3% for 48-hour exposure. The tape lift percent area coverage increased by 2.5% near sample ends and 0.35% in the middle after AO exposure.

The private equity industry has become a progressively more critical source of capital and effective governance for companies. The majority of capital raised by private equity funds is used for leveraged buyouts, with total funds under management amounting to R109 billion in 2009 for the South African industry. These funds are typically enhanced with additional deal level debt financing for each buyout thus representing, ex-ante, an active capital structure decision. The objective of this study was to understand the determinants of decisions on the extent and type of leverage used in LBOs, and attempts to explain why the observed financing choices were made by the individual private equity firms. Buyouts totalling over R 26 billion and spanning the period 1998 to 2010 are analysed. The findings are consistent with the predictions of the agency costs, trade-off and market timing theories of capital structure decisions; while little support is found for the pecking order and signalling theories. The results indicate clear patterns that lead to the supposition of an underlying model in which LBO sponsors seek to balance potential leverage related benefits with leverage related costs. The study also finds suggestive evidence indicating that the LBO financing package is designed methodically to respond to differences across firms in their size and maturity, growth prospects, in the variability of their earnings, and to a lesser extent the tangibility of their assets. Copyright / Dissertation (MBA)--University of Pretoria, 2010. / Gordon Institute of Business Science (GIBS) / unrestricted