2003 Higher Degree Theses
The following postgraduate students were awarded higher degrees for their theses in 2003
Click on the title to read the summary of the thesis
Doctor of Philosophy
Michael Bambach, Thin-Walled Sections with Unstiffened Elements Under Stress Gradient
Behrooz Ghahremannejad, Thermo-Mechanical Behaviour of Two Reconstituted Clays
This thesis is an investigation of the behaviour of unstiffened elements with stress gradients, and thin-walled sections that contain unstiffened elements with stress gradients. The primary aim of this thesis is to produce accurate design methods for thin-walled sections that contain unstiffened elements with stress gradients. The main conclusion of the thesis is that thin-walled sections that contain unstiffened elements with stress gradients may be designed accurately with the design proposals set out within this thesis, relating to elements and sections in bending. These design proposals have been balloted for both the Australian Standard for Cold-Formed Steel Structures AS/NZ 4600 (1996) and the American Specification for Cold-Formed Steel Structures AISI (1996).
The project involved an extensive experimental investigation of unstiffened plate elements, where 80 mild steel plates simply supported on three sides (with the remaining longitudinal edge free) were tested under strain gradients varying from pure compression to pure bending. Numerical (finite element) analyses were developed and compared with the test results, and used to extrapolate the experimental investigation to investigate loading conditions that could not be achieved in the experimental program.
The results of the experimental and numerical investigations were used to develop design methods for unstiffened elements with stress gradients, and thin-walled sections that contain unstiffened elements with stress gradients. The design methods are presented in the form of specific proposals to the Australian Standard for Cold-Formed Steel Structures (AS/NZ 4600). The proposals are intended for Clauses 2.3.2 and 126.96.36.199 of the specification, relevant to elements and sections in bending respectively. The proposals are shown to compare well with section test results of thin-walled sections that contain unstiffened elements with stress gradients.
The main achievement of this thesis includes:
· a model and associated infrastructure capable of simulating processes in any project phase and against the relevant project business and life cycle objectives;
· statistical output that depicts the process performance.
Therefore, it can be used for:
· Optimisation of project scope and final investment decisions across project life cycle;
· Holistic analysis and evaluation of functionality and operability of the end facility using business objectives;
· Scenario analysis offering an integrated environment to interactively apply "what-if" planning;
· Early problem detection in capacity planning and optimisation investment decisions; and
· Continuous evaluation of risks and uncertainties arising from market fluctuations vis-à-vis facility capabilities.
A deeper understanding of the process simulation concept integrated within a life cycle project management model is explained in Chapter 1. The project management model, known as Life Cycle Project Management (LCPM), has already been developed, which promotes an holistic and integrative project development and management approach. A computer application software dubbed: Dynamic Simulation Modelling System (DSMS), has been designed and developed to prove the validity of the model synthesized, i.e. process simulation technology can contribute to development of optimal project concepts, particularly within the life cycle project management model. The modelling methodology put forward, facilitates examination and planning of the hierarchical and modular structure of project processes interactively. Enhanced modelling features and logical division of large systems into smaller process components as well as their internal linkages are the key contributions of this thesis. Its aim is to apply simulation techniques to evaluate the overall project functionality from a business perspective. LCPM employs a set of target business objectives (known as Life Cycle Objective Function, [LCOF]), as the basis for decision making throughout the project's life.
Also reported are the results of 3 case studies, conducted to test and validate the model. This thesis demonstrates that discrete event simulation technique, applied through an interactive approach, is capable of providing valuable insights regarding a project's capability to meet the expected functionality criteria. Through the computer-assisted system developed, it is possible to simulate the end deliverable of the project. When this technology is coupled with scenario planning, it can lead to proactive refinement of project scope and its functional configuration. In short, the thesis demonstrates that it is indeed feasible to apply simulation technology effectively and productively on complex projects. Object-oriented programming language with object-oriented database technology facilitate the necessary modelling capability.
The effect of temperature on soil behaviour has been the subject of many studies in recent years due to an increasing number of projects related to the application of high temperature to soil. One example is the construction of facilities for the disposal of hot high level nuclear waste canisters (150-200°C) several hundred meters underground in the clay formations. Despite this, the effects and mechanism by which temperature affects the soil properties and behaviour are not fully known. A limited amount of reliable experimental data, technological difficulties and experimental methods employed by different researchers could have contributed to the uncertainties surrounding the soil behaviour at elevated temperature. Also several thermo-mechanical models have been developed for soil behaviour, but their validity needs to be examined by reliable experimental data.
In this research, efforts have been made to improve the experimental techniques. Direct displacement measuring devices have been successfully used for the first time to measure axial and lateral displacements of clay samples during tests at various temperatures. The thermo mechanical behaviour of two reconstituted clays has been investigated by performing triaxial and permeability tests at elevated temperature. Undrained and drained triaxial tests were carried out on normally consolidated and over consolidated samples of M44 clay and Kaolin C1C under different effective stresses, and at temperatures between 22°C and 100°C. Permeability tests were carried out on samples of M44 clay at temperatures between 22°C and 50°C. The effects of temperature on permeability, volume change, pore pressure development, shear strength and stiffness, stress strain response and critical state parameters for different consolidation histories have been investigated by comparing the results at various temperatures. The results are also compared with the predictions of two models.
It has been found that at elevated temperature the shear strength, friction angle and initial small strain stiffness reduce whereas permeability increases. The slope of the swelling line in the n p´ plane has been found to reduce with temperature. The slope of the isotropic normal consolidation line (INCL) and critical state line (CSL) in the n p´ plane, l, have been observed to be independent of temperature, but both the INCL and the CSL shift downwards to lower locations as temperature increases. The deformations during drained cooling and re heating cycles have been found to be elastic and to simply reflect the expansivity of the soils solid particles. The thermal volume changes during undrained heating have been observed to be direct results of the thermal expansion of water and clay particles. The internal displacement measuring devices have been found to produce reliable data for the variation of strains at elevated temperature.