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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

BOT and OMT contracts for infrastructure in developing countries

McCarthy, Sean Cormac January 1991 (has links)
This thesis is concerned with the contractual arrangements for infrastructure projects in developing countries associated with: - Build-Operate-Transfer (EOT) projects, - Operation and Maintenance (O&M) contracts and - Training contracts for operation and maintenance. The focus is placed on four sectors of infrastructure namely roads, power, water and buildings. In the literature review the nature of infrastructure projects in developing countries and the associated institutional problems are considered. The literature on topics of EOT, O&M contracts and Training contracts is surveyed. Under the EOT approach, a concession is granted by the client for the finance, design, construction and operation of a piece of infrastructure for a fixed period at the end of which the asset is transferred free of charge to the client. This thesis looks at the contracts, the corporate structure, the risks, the conflicts of interest and the advantages and disadvantages of the EOT model. A fundamental analysis of O&M contracts is then presented with the aim of providing guidance for the production of O&M contract documents. Good principles of instruction are identified and applied to the production of a draft training contract for operation and maintenance.

Fluid-structure interaction analysis of the strong and weak coupling partitioned method

Lim, Wen Zyn January 2014 (has links)
No description available.

Improving the resistance to progressive collapse of steel and composite frames

Vidalis, Carolos Antonios January 2014 (has links)
Several well publicised examples of progressive collapse have heightened concerns about the need to address robustness as a design requirement. Although research around the subject has been aimed at understanding the mechanics of progressive collapse, little work has been done on translating findings into better guidance on how to ensure adequate resistance without relying on the current prescriptive rules. Based on the Imperial College London method, which provides a soundly based analysis framework for calculating and comparing the performance of different designs, the work presented herein introduces a methodology for making realistic and effective design interventions, in order to allow designers to effectively enhance the robustness of their structure. This strategy is illustrated for both steel and composite frames and covers structures designed for both seismic and non seismic locations. Using the proposed step-by-step methodology, it is possible to redesign a simply designed composite frame in a way that it will be sufficiently robust to cope with any sudden column removal scenario. Comparison with simply increasing tying capacity reveals that the latter does not have a direct and proportional effect on the frame’s resistance and should be used within a more informed context. With the aim of performing a complementary study for moment resisting steel frames, three types of popular welded connections are modelled under progressive collapse loading conditions using the Component Method. Also, an analytical solution for the prediction of the response of irregular beam systems under sudden column loss is presented. Despite the excellent performance of most floor systems, moment frames are found vulnerable to certain column loss scenarios. Thus, these scenarios are further examined with the express purpose of identifying how the frame might best be configured so as to provide the necessary resistance. The findings show how design for seismic resistance and design to resist progressive collapse do not necessarily align and highlight which structural properties are the most important to consider in each frame type, therefore encouraging the use of the proposed redesigning methodology, which is capable of effectively remediating robustness by efficiently addressing localised weaknesses.

The microwave induced pyrolysis of problematic plastics enabling recovery and component reuse

Goodman, Steven January 2014 (has links)
Recent trends toward the effective utilisation of petroleum derived materials to increase the sustainability of their use (both for economic and environmental reasons), has resulted in an increased interest in the development of recycling methods for plastics including Acrylonitrile- co-Butadiene-co Styrene and Poly Vinylchloride. The recycling of these waste plastics that include mixed monomer compositions and halogens poses a great problem, with their decomposition making them hard to recycle due to loss of their material properties or through the production of problematic compounds e.g. HCl, PCBs, PCDD, and PCDF etc. This work has investigated the microwave induced decompositions of these plastics and explored the potential of a carbon (a microwave absorber) assisted microwave decomposition process. This culminated in the examination of the carbon assisted microwave decomposition of ABS and the potential of a one and two step process for the de-hydrochlorination, then pyrolysis of PVC, which is an untried and novel approach for PVC recycling. . The influence of microwave power, exposure time, along with the effect of the proportion of carbon, was investigated for its influence upon the yields of gases, oils, chars and product components. The proportions of gases, oils and chars were quantified in terms of their product distribution and subsequently analysed for their properties/composition by TGA, FT-IR, GCMS, Py-GCMS and bomb calorimetry. From their analyses product distributions in the oils and gases were derived and decomposition mechanisms evaluated. From these investigations it was found that the microwave decomposition process of both plastics was possible and demonstrated great versatility, with oil yields for ABS of between 2wt.% to 70wt.% and gas yields of 28wt.% to 77wt.% achieved in processing times as little as 3 minutes. From this it was also possible to identify that high quantities of monomer were also able to be recovered, significantly greater than that of a thermal process (39.5%TiC as to 34.5%TiC respectively for styrene monomer). For PVC, it was identified by initial investigations that the de-hydrochlorination of PVC was possible, confirming results of Ito et al., (2006) and Moriwaki et al., (2006). However, the discovery of amplitude dependent heating was of significant interest, not previously identified in any microwave decomposition process. It was also recognized that pyrolysis was not possible after de-hydrochlorination of PVC occurred as a result of the reduction in the materials ability to absorb microwaves (lesser dielectric constant), due to chlorine was removal. Hence it was necessary to investigate the use carbon additive to enable achieving sufficient temperatures to induce the pyrolysis of the remaining polyene structure. The identification of key parameters and ensuing relationships with microwave power, heating rate and temperatures was identified herein, giving the first detailed account of the relationship between specific polymer types and microwaves during a pyrolysis process.

Exploring critical-state behaviour using DEM

Huang, Xin January 2014 (has links)
The critical state soil mechanics (CSSM) framework originally proposed by Schofield & Wroth (1968) has been shown to capture the mechanical behaviour of soils effectively. The particulate implementation of the discrete element method (DEM) can replicate many of the complex mechanical characteristics associated with sand. This research firstly shows that the CSSM framework is useful to assess whether a DEM simulation gives a response that is representative of a real soil. The research then explores the capacity of DEM to extend understanding of soil behaviour within the CSSM framework. The influence of sample size on the critical-state response observed in DEM simulations that use rigid-wall boundaries was examined. The observed sensitivity was shown to be caused by higher void ratios and lower contact densities adjacent to the boundaries. When the void ratio (e) and mean stress (p') of the homogeneous interior regions were considered, the influence of sample size on the position of the critical state line (CSL) in e-log(p') space diminished. A parametric study on the influence of the interparticle friction (μ) on the load-deformation response was carried out. The macro-scale stress-deformation characteristics were nonlinearly related to μ and the particle-scale measures (fabric, contact force distribution, etc.) varied systematically with μ. The limited effect of increases in μ on the overall strength at high μ values (μ > 0.5) is attributable to transition from sliding-dominant to rolling-dominant contact behaviour. A μ value higher than 0.5 leads to a CSL in e-log(p') space that does not capture real soil response. True-triaxial simulations with different intermediate stress ratios (b) were performed. The dependency of strength on b agreed with empirical failure criteria for sands and was related to a change of buckling modes of the strong force chains as b increased. DEM simulations showed that the position of the CSL in e-log(p') space depends on the intermediate stress ratio b. This sensitivity seems to be related to the dependency of the directional fabric anisotropy on b. The link between the state parameter and both soil strength and dilatancy proposed by Jefferies & Been (2006) was reproduced in DEM simulations. A new rotational resistance model was proposed and it was shown that the new model can qualitatively capture the influence of particle shape on the mechanical behaviour of sand. However, it was shown that the effect of rotational resistance is limited and to quantitatively compare the DEM simulation results with laboratory testing data, e.g., the critical-state loci, it is necessary to use non-spherical particles.

Hydro-mechanical coupling in numerical analysis of geotechnical structures under multi-directional seismic loading

Han, Bo January 2014 (has links)
This thesis numerically investigates the seismic behaviour of geotechnical structures under multi-directional loading by employing the coupled hydro-mechanical (HM) formulation of the Imperial College Finite Element Program (ICFEP). The scope of the research work can be summarised as follows: Firstly, the stability of the generalised-α method (CH method) for the coupled consolidation formulation, is analytically investigated for the first time and the corresponding theoretical stability conditions are derived. The analytically derived stability conditions are validated by finite element (FE) analyses considering a range of loading conditions and soil permeability values. Secondly, the site response due to the vertical component of the ground motion is systematically investigated by employing analytical and numerical methods. The compressional wave propagation mechanism in saturated porous soils is investigated by the coupled HM formulation. Furthermore, the undertaken coupled FE analyses explore the effects of the parameters characterising the hydraulic phase, i.e. the soil permeability and soil state conditions, on the vertical site response. Thirdly, three-directional (3-D) site response analyses are conducted for the HINO site of the Japanese KiK-net down-hole array earthquake monitoring system. Different aspects of the numerical modelling for the site response analysis, such as the constitutive model, the use of 3-D input motion and the coupled consolidation formulation, are investigated and validated by the recordings from the KiK-net system. Further parametric studies investigate the impact of the variation of the water table, the soil permeability and the 3-D input motion on the multi-directional site response. Finally, the seismic response of a well-documented Chinese rockfill dam, the Yele dam, is investigated with the dynamic plane-strain FE analysis, accounting for the HM coupling and nonlinear soil response. The numerical predictions are compared against the available static and dynamic monitoring data, which allows for a rigorous validation of the developed numerical model. Furthermore, parametric studies of the Yele dam are conducted to explore the effects of several critical factors on the seismic response of rockfill dams, i.e. the reservoir simulation method, the permeability of materials comprising the dam body, the vertical ground motion and the reservoir water level.

A framework to assess the ability of automation to deliver capacity targets in European airspace

Tobaruela Arnedo, Gonzalo January 2015 (has links)
The maximum number of flights that the Air Traffic Management (ATM) system can safely and efficiently control over a period of time i.e. airspace capacity, has become a limitation over the last decade, due to a rapid increase in air traffic activity. Therefore, the ATM system in developed countries is undergoing a series of modernisation initiatives to ensure that the future ATM system is able to provide sufficient capacity to safely meet future air traffic demand. As a result, there is a need to assess if the proposed changes can effectively be translated into the desired increase in capacity. This thesis addresses this issue by developing an en-route airspace capacity estimation framework, able to measure the impact of future ATM system modernisation deployments on airspace capacity. In order to do this, it identifies the key airspace capacity drivers for current and future operations, focussing on three areas: air traffic controller workload, air traffic predictability and Air Traffic Control (ATC) centre cost-efficiency. In each of the three framework areas, the research develops methodologies that overcome the deficiencies of existing capacity estimation techniques. This leads to an innovative multi-dimensional approach to airspace capacity estimation, able to reflect the different relationships of airspace capacity with the framework areas. The framework quantifies the relationship between the ATC centre planning process accuracy and airspace capacity. It estimates the effect of increased predictability on airspace capacity through the performance of the Airspace Management and Air Traffic Flow & Capacity Management functions. Finally, it computes air traffic controller workload with considerable accuracy (up to 80% of the actual workload) during medium-low workload scenarios and reflects the workload trend (Spearman's rank coefficient = 0.72) during high workload scenarios.

Impact of Dubai Metro on property values

Mohammad, Sara Ishaq January 2014 (has links)
Despite the large number of case studies estimating the impact of railways on property values, there is as yet no research conducted specifically for the Dubai Metro. This study applies the existing empirical methods, corrected for sources of bias, to test for the effect of the Dubai Metro on the values of residential and retail properties. The results will also be of interest to neighbouring cities developing their first railways. The existing empirical work reveals a large variation in estimates for the effect of railways on property values. This thesis provides a comprehensive meta-analysis examining the sources of variation and relating these findings to the estimates for the Dubai Metro. As an addition to the existing literature, this study examines the effect on sale and rent values using repeated cross-sectional and pseudo panel data, and makes a case for the preferred data structure. Besides applying the known measures of accessibility to a metro, this research represents the first attempt to test for the effect of the change in the generalized cost of travel (GC) due to the operations of the metro. The results from the preferred models indicate negative, insignificant and positive impacts of the metro on the sale value of dwellings located at different distances. The metro also enhances the rent value of dwellings and the sale value of retail properties. The study also finds an increase in the value of dwellings due to a decrease in the GC. The results suggest that while a reduction in the GC of public transport boosts the sale value of retail properties, values are higher in areas with higher private and public transport trip rates. The positive effect of the metro implies that a value capture mechanism can be explored, provided the related policy implications are understood.

A comparative optimisation study of activated carbon production from hazelnut shells by thermal and microwave heating methods

Sharifan, Suzan January 2014 (has links)
This research has studied the optimisation of activated carbon production from waste hazelnut shells, using both conventional and microwave heating techniques. A comparative study was conducted on the results obtained from both production methods to provide information on the characteristics, advantages and disadvantages of each production technique from a physical and chemical perspective. The study of the conventional production method was carried out using a comprehensive two- stage Response Surface Methodology (RSM). The microwave production method was studied using a combination of RSM and the traditional single-factor-at-a-time experimental design. The comparison of the two production methods showed that at a similar degrees of carbon burn- off, much lower pore volume and internal surface area was achieved for the microwave produced samples. The highest BET surface area produced with the conventional production method was 1777 m2/g, obtained from the activation of carbonised char with 0.67 ml/min water for 4 hours at 900°C. This value was nearly 2.5 times larger than the maximum BET surface area achieved from the microwave production method (715 m2/g) (50 min at 1000W). Similar results were also obtained for the aqueous phase adsorption of phenol and methylene blue; 2.2x and 2.3x larger adsorption capacity for thermal sample, respectively. In general, the microwave production method was found to be less effective in the production of highly microporous carbon. While the rate of micropore development with carbon burn-off in microwave heating was much lower than the conventional method, mesopore volume was found to be close and even comparable with that achieved with the conventional method. Considering that the microwave heating resulted in lower energy consumption per unit carbon burn-off, this heating system can be energy efficient in the production of mesoporous adsorbents. The energy efficiency could be of great importance when a two step carbonisation- activation is to be employed, since it could considerably reduce the heating time to the final activation temperature.

Design of structural steel elements with the Continuous Strength Method

Liew, Andrew January 2014 (has links)
The current practice of ultimate limit state design for steel structures involves an elastic--perfectly plastic material model and the classification of cross-sections into discrete behavioural classes. This leads to a design philosophy which is simple, but generally over-conservative. The Continuous Strength Method is a strain based design approach which allows for the beneficial influence of strain hardening. At the core of the method is a base curve which relates the deformation capacity of a cross-section to its cross-section slenderness. Deformation capacity is defined through a strain ratio, which is the ratio of the maximum strain that a cross-section can endure to its yield strain. The formulation for the base curve was derived by means of stub column and bending tests collected from the literature. Knowing the limiting strain and assuming plane sections remain plane, the resistance of cross-sections to combinations of axial load and bending moments can be calculated by integrating the stresses arising from a suitable strain hardening material model over the area of the cross-section. Analytical and design expressions have been developed, and the resistance predictions for open and closed cross-section shapes have been compared with existing collated test data, and shown to give additional capacity over current design approaches, with a reduction in scatter and a more consistent method. Beyond the analysis of the cross-section, the method has been extended to the global instability of pin-ended columns by utilising moment--curvature--thrust curves. The curves were paired with an assumed buckled displacement shape to find applicable equilibrium configurations, and to extract the peak axial loads for producing buckling curves. The column buckling curves showed two distinct regions based on the global slenderness of the column. Firstly a region of global-dominated failure, where the columns failed by a loss of overall flexural rigidity, and secondly a local-dominated failure region, where the mid-height cross-sections failed by local buckling. The local cross-section failure mode allowed for axial loads greater than the cross-section yield loads. The column buckling curves were found to be dependent on the initial out-of-straightness, the cross-section geometry and the material yield stress. An experimental program provided insight into the cross-section resistance of hot-rolled rectangular hollow sections (RHS). The experiments included 32 material tensile coupon tests, eight stub column tests and four simply supported beam tests, and exhibited little strain hardening. Overall, a series of developments to a strain based approach for steel structures has been presented, and areas for future developments have also been highlighted.

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