The thesis presents the minimum-cost designs of reinforced concrete beams and frames involving costs of concrete, reinforcing steel and formwork, subject to deflection and strength constraints, in addition to upper and lower bounds on design variables. The design variables are cross-sectional dimensions and reinforcing steel. The optimization is carried out using the methods based on optimality criteria - continuum-type optimality criteria (COC) and discretized continuum-type optimality criteria (DCOC). The performance of the structure is defined in accordance with the philosophy embedded in the limit state design (LSD) (CEB/FIP, 1990; SAA, 1988; Warner et al., 1988; Ferguson, 1979). The advantages and disadvantages of the various structural optimization methods are discussed to arrive at the right choice of the technique to be used for the solution of the minimum-cost design problems of these structures.

The thesis begins with a brief review of structural optimization and of the reasons why the COC and DCOC based methods are highly efficient for the sizing optimization of large structural systems. The basic principles of the COC are explained using simple RC beams whose design variables are allowed to vary freely. These are then extended to beams whose design variables are segment-wise uniform. The principles of DCOC are introduced using multispan beams whose design variables vary freely or are uniform in a span. The cross-sections of members can have rectangular or T shape, The DCOC method is then extended to treat more complicated RC structures such as frames. Moreover, situations in which the minimum-cost design problem includes only the strength and side constraints are also considered. It is shown in particular that the COC/DCOC-based methods are the most efficient when the number of design variables and constraints is large, as is always the case with RC structures of practical significance.

The minimum-cost design problems of RC structures are systematically formulated, the minimality conditions are explicitly derived, and suitable algorithms are developed. The usefulness, efficiency and versatility of the algorithms developed for each of the considered design problem are demonstrated by using several test examples.

ANANGA, NYARBA
GEODETIC POSITIONING AND MONITORING OF TIDE GAUGE DATUMS
PhD thesis - Supervisor: Dr R Coleman

The purpose of this research is to provide a unified vertical datum (zero epoch) for number of selected sites so that this defined datum can be used to monitor mean sea level, relative to a locally fixed tide gauge benchmark (TGBM). The aim is to incorporate in a rigorous adjustment model using a wide variety of observational data, such as terrestrial levelling, GPS coordinate solutions and coordinate solutions from other space-based techniques, namely Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR), such that the local, regional and global network solutions are combined. A fiducial concept is adopted in which a subset of coordinates are constrained to values previously determined from VLBI and SLR solutions. Initially, the TGBM's are organised into a local network, and finally into a regional and global network where each tide gauge is fixed relative to a unified vertical datum.

A variance-covariance model was developed to generate the VCV matrix of a homogeneous or heterogeneous data set of a secondary network adjustment using multi-session/station solutions of a phase adjustment. In this case it is not necessary to use the VCV matrix generated from various GPS softwares for a secondary network adjustment.

A new statistical approach is also developed using the analysis of variance test which is applicable to either baseline solutions or multi-session/station solutions.

Finally, we developed strategies to monitor the tide gauges by computing an internal reference (mean coordinates) datum (which we called zero-epoch), and the variations between these zero-epoch coordinates and the single session solutions (coordinate differences) are determined. The determined zero-epoch approach was used to determine the high precision and stability of the Australian permanent and fiducial sites connected to other continental sites using the Antarctica GPS Surveys.

Using data for Australia, a regional (common) vertical datum was established to accurately fix the tide gauges and also to establish the compatibility between the different coordinate solutions. A comparison of results from the GPS, VLBI and SLR network solutions indicated that the GPS-VLBI difference was within 2 parts in 10⁷ in the horizontal components and 3.8 cm in the height component, while the GPS-SLR difference was within 5 parts in 10⁷ in the horizontal components and 4.0 cm in the height component. The overall precision of the height displacements of the permanent and fiducial sites of Australia were within ± 2 cm and demonstrates that the proposed methodology is an effective way to maintain a vertical reference datum.

BAWEJA, DAKSH
STEEL CORROSION IN AUSTRALIAN PORTLAND AND BLENDED CEMENT CONCRETES
PhD Thesis - Supervisor: A/Professor H Roper

Work in this Thesis focused on the corrosion of steel in a range of solution electrolytes, pastes and concretes. A series of experimental methods was used to study corrosion of steel. These included gravimetric and corroded area measurements, concrete resistivity, corrosion potential, potentiodynamic anodic polarisation, polarisation resistance, electrochemical impedance spectroscopy and electron microscope studies. Four binder types, a high C₃A cement, a low C₃A cement, a slag blended cement and a fly ash blended cement were used to prepare solutions, pastes and concretes. Solution liquors were derived from portland and blended cements at a water:binder ratio of 2.0. Other electrolytes used were saturated Ca(OH)₂, tap water and distilled water. Pastes were cast at a water:binder ratio of 0.45. Concretes cast had water:binder ratios of 0.45, 0.55, 0.65 and 0.85.T

he degree of steel passivity was similar in saturated Ca(OH)₂ solutions to those of steel in the four binder solutions in the absence of chlorides. Steel in contact with the binder solutions showed significantly higher threshold chloride ion concentrations for depassivation than steel in contact with the saturated Ca(OH)₂ solution. Steel surfaces exposed to the slag and fly ash blended cement solutions showed the surface to be partially coated with a thin film. No such film was found on steel surfaces exposed to the high C₃A and low C₃A cement solutions. For paste coated steel working electrodes partially immersed in 3% NaCl solution, paste resistance was found to decrease with time for working electrodes having a 1 mm and 3 mm cover. Paste resistances were found to increase with time for a 7 mm cover reflecting the effects of continued hydration and pore refinement through contact with the 3% NaCl solution.

Concrete water:binder ratio was found to significantly influence corrosion of steel in concrete. Binder type also significantly influenced corrosion but not to the extent of the water:binder ratio. Three distinct stages of corrosion were observed when the corrosion current was plotted against the concrete resistivity, namely the Quiescent Stage (low corrosion), the Active Stage (increasing corrosion) and the Breakaway Stage (high corrosion). Studies were conducted into the possibility of using the half cell potential and concrete resistivity ratio as a means of estimating the corrosion current for reinforcement within concrete. It was found that a value proportional to the corrosion current could be obtained. Relationships between corrosion potential and the corrosion current were found for reinforcement within concrete where a B value of 26 m V was applied. Better correlation coefficients were found for similar data where B was calculated from half cell potential data using a series of derived Equations. Significant trends were also found between gravimetric weight losses and electrochemical weight losses determined using polarisation resistance data. Correlations improved when data were separated into those for the portland cement concretes and those for the blended cement concretes and when B was derived from Ecorr. Both potentiodynamic anodic polarisation and polarisation resistance methods were successfully used to predict the gravimetric weight loss of steel in concrete for the set of reinforced concrete slabs considered. Better predictions of weight loss were found using the potentiodynamic anodic polarisation procedures described in this Thesis than those obtained using polarisation resistance procedures described in the literature.

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BENEKE, DAVID L
AERODYNAMIC EFFECT OF WIND-INDUCED TORSION ON TALL BUILDINGS
Master of Engineering (Research) Thesis - Supervisor: A/Professor KCS Kwok

A wind tunnel investigation was undertaken to compare the wind-induced torsional response of high-rise structures of varying cross section. Previous research into this topic has revealed that torsional response is significant when compared to the cross-wind and along-wind components. Little is known at the present time of how the mechanisms of wind-induced torsion are affected by changes in building shape.

Four different model buildings were tested in a boundary layer wind tunnel. The cross-section of each model corresponded to a basic shape; rectangular, diamond, triangular and D-shaped. Properties such as aspects ratio, building density and damping were similar for all four models. Each of these models was mounted on a torsional aeroelastic rig to investigate the aerodynamic effect in different wind environments. Each model was tested at varying reduced velocities and angles of wind incidence under wind conditions corresponding to Terrain Categories 2 and 4 as set out by the Australian Standard Wind Loading Code AS1170.2-1989.

Results indicate that wind-induced torsional response varies dramatically with changes in building cross-section. The triangular and rectangular shaped models recorded a torsional response which was the highest of all models tested. Torque spectra for these two models indicated that at certain angles of wind incidence and reduced velocity, displacement dependent excitation associated with flow reattachment and wake excitation were apparent. The torsional response of the D-shape model was smaller than that of the rectangular model. The diamond model yielded significantly lower torsional response of which turbulence buffeting was the dominant excitation mechanism.

A simplified estimation procedure suitable for inclusion in wind loading codes was derived from the results obtained for the wind-induced torsion on buildings with basic cross-sections.

This enables designers to incorporate the predicted wind-induced torsional moments into the design of tall buildings, in addition to those for along-wind and cross-wind effects.

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BERNARD, ERIK STEFAN
FLEXURAL BEHAVIOUR OF COLD-FORMED PROFILED STEEL DECKING
PhD thesis - supervisor: A/Professor RQ Bridge and Professor GJ Hancock

Local and distortional buckling are forms of sectional instability which may occur in the compressed flanges of thin-walled profiled steel decking panels loaded in flexure. Local buckling is restricted to the flat elements between folds in a section and involves out-of-plane straining of stiffening elements. Distortional buckling may occur in such a manner that in-plane strong of plate elements takes place. This mode of buckling typically results in displacements of stiffeners normal to the plane of a flange. In this thesis, the influence of intermediate stiffeners on the buckling behaviour of compressed flanges has been studied by experimental and numerical means.

A programme of laboratory tests on brake-pressed and roll-formed profiled steel decking panels exhibiting local and distortional modes of elastic buckling is described. A test rig was developed that successfully approximated the boundary conditions implied by a comparative numerical model and prevented premature failure due to localised stressing at the specimen ends. The specimens, consisting of ‘V’ and 'flat-hat' stiffened trapezoidal decks, as well as standing seam and dove-tailed decking panels, were manufactured by cold brake-pressing or roll-forming using high tensile strength coated steel strip. The specimens were loaded in pure bending and their performance studied to the point of ultimate failure. A finite strip analysis was used to model the buckling behaviour to gain a better theoretical understanding of thin-walled stability.

Other aspects of thin-walled structural behaviour affecting the performance of the decking panels, including residual stress, material properties and flange curling, were also investigated. A detailed study of geometric imperfections, and methods of precisely measuring geometry, was undertaken.

The results of the experimental and numerical investigations are compared to estimates of ultimate moment capacity determined using a number of design standards. Comparisons are also made with estimates based on several proposed design methods, including a new design method proposed by the author. Measured flange curling deflections are compared to estimates determined using an existing design standard.

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CHAN, MUNG TAK
A TWO-DIMENSIONAL WAVENUMBER SPECTRUM FOR WIND-GENERATED SHORT WAVES
Master of Engineering (Research) Thesis - Supervisor: Dr ISF Jones

A new relationship for growth rate, which describes the transfer of momentum from the wind to surface waves is obtained based on published data taken in wind-wave tanks experiments in the gravity-capillary range for wavenumber greater than that at the peak of the sea spectrum, when compared with experimental data. The proposed growth rate relationship is given by

where u_* is the friction velocity, c is the phase speed, s is some constant, q is the angle between the wavenumber vector and the wind direction, k is the magnitude of the wavenumber vector, and km is the wavenumber at phase speed minimum. We have also assumed that there is an approximate balance between the wind input and dissipation to derive, by dimensional analysis, a wavenumber spectrum. With the empirically determined constants and spreading function for the angular distribution of wave energy, a wavenumber spectrum is formulated for k > k_p , where k_p is the wavenumber at spectral peak. The derived directional wavenumber spectrum is given by

with

where q _w represents the mean wave direction, and h is a function of k/k_p . The corresponding two dimensional wavenumber spectrum is

where

The proposed model provides a good prediction of measured data including many of the Bragg backscattering, and mean square wave slopes results acquired both from the ocean and the laboratory. In the analysis, the models are also used to predict wave-induced stress.

CHEN, GUANGNAN
INELASTIC TORSIONAL BEHAVIOUR OF THIN-WALLED STEEL MEMBERSP
PhD thesis - Supervisor: Professor NS Trahair

Thin-walled open section steel members are widely used in many engineering structures and may subject to torsional loading. Owing to their inherent lack of torsional stiffness and strength, a realistic prediction of torsional behaviour must consider both the material and the geometric nonlinearities.

A simple mitre shear strain distribution model for elastic and inelastic uniform torsion is presented. Instead of dealing with the complicated two-dimensional governing differential equation, a simple shear strain distribution is developed from the mitre model. This allows the influence of transverse uniform torsion shear stresses at the free ends of flanges to be fully and explicitly accounted for. As the mitre model with suitable adjustments is able to provide both the fully elastic and the fully plastic solutions, a torque-twist relation of high accuracy is obtained in the intermediate elastic-plastic range. The mitre model can be combined with the simple one-dimensional beam theory of bending and warping so that a simple method is obtained for predicting the stresses under combined flexure and torsion.

An one-dimensional nonlinear finite element model is presented. By making use of the simple strain distribution based on the mitre model and Vlasov's thin-walled beam theory, the present model is featured by a two-noded line-element with a 'fibre model' of the stress-strain relationship which accurately simulates the spread of inelastic zones. In order to treat the material nonlinearity, an advanced material state determination algorithm has also been employed. The complete nonlinear load-twist path is traced by the variable arc-length method combined with the modified Newton-Raphson method. The program is used to study the inelastic nonuniform torsion of steel I-beams, the torsional strengths of cruciform columns, and the biaxial bending and torsion of general thin-walled steel members.

CHEN, LIEFENG (Tony)
THE EFFECT OF LATERAL SOIL MOVEMENTS ON PILE FOUNDATIONS
PhD thesis - Supervisor: Professor H Poulos

In order to investigate the effect of lateral soil movement on piles, numerical and experimental work has been carried out in this thesis, and consists mainly of three aspects; firstly, development of a combined finite and infinite element analysis of lateral pile behaviour; secondly, performance of a series of laboratory experiments on single piles and pile groups, and thirdly, investigation of the ability of an existing boundary element program to predict the lateral pile response.

The combined finite and infinite element analysis was used mainly to develop the ultimate lateral soil pressure p_u for group piles, embedded in both cohesive soils and sandy soils. Generally speaking, the group effect was found to have a significant effect on the p_u value, with the extent of the group effect being dependent on a number of factors, including pile loading condition (e.g. whether the pile was subjected to lateral loading or lateral soil movement), soil stress state, type of soils (e.g. cohesive soils or sandy soils), pile arrangement, pile spacing, and pile position in a group. The developed solutions were also compared with some experimental results and reasonable agreement between the theoretical and experimental results was found in some, but not all, cases.

In the laboratory experiments, a triangular soil movement profile (with the maximum at the top and zero at a certain depth) was imposed on model piles embedded in calcareous sands. The maximum bending moment induced in a single isolated pile was found to be dependent on, among other factors, pile embedded length, pile diameter (and stiffness), and the pile head fixity condition. The group effect was also found to have a significant influence on the maximum bending moment for a pile in a group, and the extent of the influence was found to be dependent on a number of factors, including pile arrangement, pile spacing, pile head fixity condition and position of the pile. It was also shown that the group effect might either increase or decrease the maximum bending moment, depending on the above-mentioned influencing factors.

The boundary element program was used to predict the laboratory experimental results and some full scale published field test results. Generally speaking, the agreement between the predicted and the measured results was fairly good, where appropriate input parameters (in particular, the magnitude of the lateral soil movement and the lateral ultimate soil pressure) were used. It was thus concluded that the program could be useful for practical use. Some guidelines for the choice of the required input parameters were also provided.

In summary, through the numerical and experimental study, a better understanding of the response of piles subjected to lateral soil movement has been achieved and some of the factors influencing this response have been identified and investigated. Key factors are the ultimate lateral pressure developed between the pile and the soil, and the depth of embedment of the pile relative to the depth of moving soil. It is anticipated that the results presented in this thesis will be of some value in the design of piles to resist externally-imposed soil movements, and that several issues requiring further research have been identified.

CROSBY, DANIEL G
WIND SPEED DISTORTIONS DUE TO THE PRESENCE OF AN OFFSHORE PLATFORM IN BASS STRAIT
Master of Engineering (Research) Thesis - Supervisor: Dr ISF Jones

Offshore oil platforms provide stable structures from which instruments, used to measure wind velocity and turbulence, may be attached. The manner in which the platforms distort surrounding wind fields has been the subject of many past studies. All of these studies involved either field measurements or wind tunnel studies in isolation. This study incorporates both wind tunnel and field measurements in an attempt to quantify the wind field distortion due to offshore oil platforms.

A series of measurements of wind field distortions was carried out on Snapper platform, an offshore oil production platform in Bass Strait, measuring 57 by 25 metres in plan. The field measurements were compared with wind tunnel measurements on a model of Snapper platform. The wind tunnel model incorporated an 'outline' design in order to reproduce the wind-flow distortion of the full-scale platform, whilst the wind structure developed in the wind tunnel was tailored to match that of Bass Strait winds.

After observing good comparisons of relative distortions between the model and full-scale platform, measurements of wind-flow distortion were subsequently made at a number of locations on the wind tunnel model. These measurements revealed that the presence of Snapper platform distorts the wind flow, to varying degrees, to at least a radius of 50 metres in certain directions. However, it was also noted that levels of wind-flow distortion appeared to be minimal at distances only 18 to 25 metres away from the southern end of the platform, a common site for past wind measurements. Whereas the influence of the platform on wind measurements at the radiomast were only of the order 2%, disturbances due to the tower itself are expected to be as high as ten percent.

DENOON, ROY OGILVIE
THE WIND-INDUCED DYNAMIC RESPONSE OF AN 84 m HIGH CONTROL TOWER
Master of Engineering (Research) Thesis - Supervisor: A/Professor KCS Kwok

An 84 m high concrete control tower of circular cross-section was instrumented to measure its dynamic response to wind loadings. Reliable full-scale data on this type of structure is very sparse and this thesis details both the instrumentation and the results obtained. The data is then used as a basis for comparison with predictions using current design methods.

The tower is located close to the central business district of Sydney and experiences very different upwind terrain types depending on the wind direction. This was found to have little effect on the tower response in the range of wind speeds encountered. Neither was there any firm evidence of the vortex shedding peak of response normally associated with circular cylindrical type structures.

The accelerations experienced in the tower under strong wind conditions were found to be unacceptable with reference to the latest human comfort acceptability criteria. Indeed, there is anecdotal evidence of employee absence due to motion in strong winds. The predictive methods used to estimate the tower's wind-induced dynamic response were AS1170.2-1989, Vickery (1992) and ESDU 85039. These were found in most cases to provide a conservative prediction for design purposes.

GHAFOORI, MOHAMMAD
ENGINEERING BEHAVIOUR OF ASHFIELD SHALE
PhD thesis - Supervisor: Professor JP Carter and A/Professor JC Small

Intact specimens of Ashfield shale have been used in this study to investigate its engineering behaviour. Ashfield shale is a sedimentary rock of the Wianamatta sequence from the geological region known as the Sydney basin in New South Wales, Australia. This rock outcrops over parts of the Sydney metropolitan area. Many structures and deep excavations have been constructed in the Ashfield shale, and it is sometimes used as a construction material.

One of the primary aims of this investigation has been to identify index property tests useful for determining the engineering properties of shale. A further aim of the study has been to evaluate the effects of lamination orientation, with respect to the principal stress directions, on the shear strength, shear strength parameters and deformation of Ashfield shale.

Thin sections, X-ray diffraction and scanning electron microscopy analysis have been used to determine the clay mineralogy and fabric of the shale. Slake durability tests have been performed on samples of shale with varying degrees of weathering to investigate the deterioration of the rock from cycles of wetting and drying. Correlations between the slake durability index, the natural water content, Atterberg limits, uniaxial compressive strength, and the weathering grade of the shale have been investigated. The natural moisture content has been found to be a good predictor and a useful index for the durability, index properties, clay content, and the strength of the intact shale.

The point load test is widely used to determine the uniaxial compressive strength indirectly. Correlations have been made between the point load strength index and the measured values of uniaxial compressive strength in direction perpendicular to laminations. The strength anisotropy, the ratio of point load strength in the strongest and weakest directions, was measured for the samples tested in these two directions.

This study also presents the results of a comprehensive series of triaxial and uniaxial compression tests on Ashfield shale. Triaxial compression tests have been performed over a range of confining pressures from 0 to 10 MPa. The orientation of the laminations, relative to the axial direction, in the triaxial apparatus has been varied between 0 and 90 degrees at intervals of 15 degrees. The lateral and longitudinal strains have been measured by gauges mounted on the core samples. These tests have been used to determine the effects of the anisotropy, caused by the laminations, on the strength and stiffness of the shale. The strength data were compared with basic failure theories and the applicability of these strength criteria for Ashfield shale was examined. Of the three criteria used for intact rock, Bieniawski's (1974) criterion appears to be the most appropriate one for Ashfield shale. The single plane of weakness theory (Jaeger, 1960) and the modified variable cohesive strength theory (McLamore and Gray, 1967) have shown good validity for Ashfield shale and fit the experimental data fairly well. The theoretical predictions also show good general agreement with the experimental values of the secant modulus of elasticity, measured at 50% of the peak strength across the full range of b (angle between lamination and axial stress direction) values.

For practical purposes a single criterion has been suggested. This criterion is capable of accurately predicting the strength of Ashfield shale over the full range of b values, and therefore capture accurately the anisotropic nature of the strength.

A series of direct shear tests has been carried out on the Ashfield shale to determine the influence of the boundary conditions on the strength parameters and the degree of anisotropy. Direct shear tests have been performed at a variety of normal stresses within the range from 0.3 to 1.6 MPa, and peak and residual strength parameters have been determined. The peak strengths were usually mobilised at relatively small shear displacements and the shearing resistance was reduced abruptly with further shearing beyond the peak. It was found that the strength parameters were significantly affected by the direction of shearing. The triaxial and direct shear experimental results confirmed the existence of anisotropy in the shear strength parameters.

A numerical study of the deformation of an anisotropic rock, such as shale, in direct shear tests is presented. The study has investigated the effects of the orientation of the bedding planes to the shearing direction, and of the boundary conditions imposed in the test. A cross-anisotropic elastic model has been used to represent the prefailure stress-strain behaviour of the rock and an extensive parametric study has been carried out of the behaviour of this material in direct shear. Implications for the interpretation of actual test data are discussed, and illustrated by comparison of the theoretical predictions with experimental results for Ashfield shale. The predicted direct shear stiffness shows good general agreement with the secant shear stiffness measured at 50% of the peak strength in the direct shear test. This implies that the direct shear test is capable of detecting accurately the nature of the anisotropy of shale. Furthermore, the secant values of the moduli determined from uniaxial and triaxial compression tests are consistent with the secant shear stiffnesses measured in direct shear tests.

GREENSLADE, DIANA
THE MODULATION OF SHORT OCEAN WAVES BY LONG WAVES
Master of Engineering (Research) Thesis - Supervisor: Dr ISF Jones

Satellite remote sensing provides an exciting new technology with which to obtain oceanographic data and has the potential to be of great benefit to ocean engineers. In particular, the Synthetic Aperture Radar has the capability to detect both waveheight and direction of propagation of long ocean waves (of wavelength » 100m). It is assumed that Bragg scattering is the mechanism responsible for the backscatter of electro-magnetic radiation from the ocean, and for the purpose of wave imaging, the ocean surface can be thought of as a two-scale model, with short, Bragg resonant waves riding, and being modulated by underlying large scale wave .

The Modulation Transfer Function relates the intensity of the radar backscatter to the phase of these long waves and for Real Aperture Radars, consists of two separate components, the modulation due, to tilting and the modulation due to hydrodynamic interactions (straining). The aim of this investigation is to determine the proportion of the backscatter modulation due to straining, and compare this with that due to tilting.

Stereophotogrammetry can be used to obtain the topography of a small area of the surface, and in this investigation six stereophotogrammetric time series were used (a total of 123 seconds of data). This data was obtained under a wide range of ocean conditions, with wind speeds ranging up to 20 m/s and Significant Wave Heights of up to 3m. Long wave profiles were obtained from these time series, and these were each divided into four sections, the crest, trough, forward and backward faces of the long waves. Two-dimensional wavenumber power spectra were obtained for each stereophotogrammetric frame and from these, information on the short, Bragg resonant waves was extracted. These were combined to obtain the mean energy of the Bragg resonant waves at the four different phase locations along the long wave profile.

It was found that the maximum short wave energy occurred on the forward face of the long wave, and that the mean short wave energy was modulated by ± 50%. This represents the short wave modulation due to straining alone, since the effect of tilting was excluded in the processing. The results were compared to the hydrodynamic theory and found to agree well for the small range of wave slopes generally found in the open ocean. These results also agreed well with previous measurements of short wave modulation in the ocean.

It was found that if the sensing tool was a microwave radar, viewing with an incidence an incidence angle of 45º, then the modulation due to straining is comparable to that due tilting, and a simple model is developed for the modulation of radar backscatter by long ocean waves.

HUANG, JIE TAI
THE EFFECTS OF DENSITY AND CEMENTATION ON CEMENTED SANDS
PhD thesis - Supervisor: Dr DW Airey

This thesis deals with the general and fundamental behaviour of cemented soils. A technique for manufacturing artificially cemented soils has been developed for this study. Tests to investigate the reliability of the specimens have shown the manufacturing process to produce uniform and repeatable specimens with pre-determined dry unit weight and cement content.

Unconfined compression and split cylinder tensile tests have been carried out on the artificial soils to investigate the variations of the index strengths with dry unit weight and cement content. These index strengths have been compared with those of various naturally cemented materials such as cemented sands and soft rocks.

Polished sections of the artificial calcareous soils and a calcarenite have been examined by electron microscopy and have shown the changing nature of the effects of cement at different densities and cement contents. The photomicrographs of the polished sections have shown many similarities in the soil fabrics created by natural and artificial cementation processes and have shown how the fabric changes as a result of mechanical testing.

The compression behaviour of the artificially cemented soils has been examined extensively by isotropic consolidation up to 60 MPa, triaxial K₀ consolidation up to 5 MPa mean effective stress and oedometer tests up to 30 MPa vertical stress. The effects of particle size, mineralogy and pore fluid on the compression responses of the soils have been studied.

A series of drained and undrained triaxial compression tests has been carried out on the artificial soils covering a wide range of dry unit weights from 13 to 19 kN/m ³, cement contents from 0 to 20% and confining stresses from 100 kPa to 20 MPa. These tests have provided a complete set of data to investigate the effects of confining stress, density and cement content on the triaxial compression behaviour of the soils. Analyses of the data have been conducted to investigate the effects of density and cementation on the pre-failure behaviour, the yield loci, failure and the ultimate states.

The results of this research indicate that the general patterns of behaviour of cemented soils can be described within the framework of critical state soil mechanics, but further development of the critical state framework is required to take into account the effects of cementation. The effects of cementation bonding are only significant below the apparent preconsolidation pressure where they cause increases in stiffness and strength. Density per se has little effect providing allowance is made for OCR.

IENTILE, FRANCIS
SPECTRAL ESTIMATION AND MODELLING OF OCEAN WAVES FROM SYNTHETIC APERTURE RADAR
Master of Engineering (Research) Thesis - Supervisor: Dr ISF Jones

Synthetic Aperture Radar (SAR) is capable of providing dense high resolution imagery of the ocean surface which is of potential value to the ocean engineer and physical oceanographer. This imagery may be processed by two dimensional spectral methods to give radar brightness spectra which are related to the directional distribution of the dominant ocean wave field components. However, as SARs are based on coherent imaging principles, image data produced is contaminated by a type of fading noise known as speckle. The multiplicative nature of speckle produces a low signal to noise ratio, making the detection of wave spectral features potentially difficult and hence the suppression of speckle in SAR data is desirable.

A review of SAR imaging principles and speckle noise with special reference to the case of ocean surface imaging is given. A small ocean surface area taken from a SIR-B SAR image of the Tasman Sea, offshore Sydney is then processed using a generalised two dimensional Fast Fourier Transform (FFT) algorithm which was specially developed for this study and includes a number of pre and post processing options. Statistical analysis of the data verifies the multiplicative nature of speckle noise while the spectral estimates obtained show that a 2D pre-whitening/post colouring scheme is isotropic and gave the best spectral estimate compared to other commonly used schemes. The problem of detecting ocean wave spectral features in the presence of speckle noise is then examined statistically for conventional "unmatched" and "matched" processing procedures, in order to identify which process provides the best estimate of the noise free functional form of the model ocean wave spectrum, in terms of a signal to noise ratio of the spectral transfer of the image The results of this analysis show that "unmatched" processing procedures provide the best estimate of model ocean wave spectrum as they produce the smallest least squares sense error due to noise present in the image and that a compromise between decreasing confidence limits and increasing the error in fitting the model exits for "unmatched" processing cases involving averaging techniques.

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LEO, CHIN JIAN
BOUNDARY ELEMENT ANALYSIS OF CONTAMINANT TRANSPORT IN POROUS MEDIA
PhD thesis - Supervisor: Professor JR Booker

There is considerable interest within the engineering profession to develop a better understanding of contaminant transport in porous media in general, and the long term performance of waste disposal and storage facilities in particular. In connection with this, it is the objective in this thesis to develop boundary integral equation and semi-analytic methods relevant to analysing the impact of contamination in porous media due to the presence of waste sources.

In the solution approach adopted throughout the thesis, a Laplace transform is used to eliminate the time variable in the governing differential equations, thus facilitating the formulation of the boundary integral equation. It will be observed that one of the notable features of this particular formulation is the absence of any domain integrals, thus giving it a distinct computational advantage over alterative methods which require time consuming integration of the domain. Independent semi-analytic solutions have been developed in conjunction with the boundary integral solutions. These are of interest in their own right as well as providing an important basis for validating the numerical results.

The study deals with homogeneous and non-homogeneous porous media, fractured and non-fractured soil or rock mass. Problems of practical interest covering contaminant leakage from waste storage facilities and the performance of engineered containment system designed for waste landfills may be analysed using the methods developed herein. Illustrative examples are provided to demonstrate the application of the solution methods to such problems.

LEONTE, MIHAI
SULPHIDE DUST EXPLOSIONS
Master of Engineering (Research) Thesis - Supervisor: Dr Roger Enright

The research program was directed towards investigating the various factors which lead to a sulphide dust explosion and if possible, the development of methods to prevent or inhibit such explosions.

The initial stage of the project was designed to determine the mass of reactive dust, produced during development blasting. A total of five cuts consisting of five 45 mm diameter blast holes and four 75 mm reamer holes three metres in length were drilled and charged with either ANFO or Powergel. The results showed that approximately 300 kilograms of reactive dust was produced when a cut was fired and indicated that the current mining techniques using limestone or water to inert the dust would not be effective.

Stemming tests using a high speed camera and a 35 mm still camera constituted the second stage of the project. Holes loaded with different types of explosive, detonators and stemming were filmed at 500 frames/sec and photographed with a 35 mm camera. In unstemmed holes, the results indicated that the flame front extended up to two metres from the hole collar with a duration of less than 4 milliseconds. Various types of stemming material were found to prevent the development of a flame front at the collar of a single blast hole.

Sulphide dust explosions were observed when single hole blasts were fired in ground with a high sulphur content. A total of 27 sulphide dust explosions were observed in 103 single hole blasts and the results indicated a flame front velocity around 250 m/s and up to 50 milliseconds duration.

MAKARCHIAN, MASOUD
UNDERPINNING OF FOUNDATIONS BY PILES
PhD thesis - Supervisor: Professor H Poulos

Existing buildings sometimes experience ongoing settlement or face the prospect of excessive settlement in the future if a change of building use is required and foundation loadings increase. Several methods of foundation enhancement are available to improve the future performance of existing foundations. One method is to enlarge the foundation dimensions, while another widely used method is underpinning by piles. In this thesis, underpinning methods are reviewed and classified and several case histories around the world are studied to show the application of those methods to existing buildings and historical monuments. It is found that, despite the fact that piles are gaining increasing application in underpinning work, design methods for underpinning piles are not well developed.

A numerical study has been carried out for a simple idealised problem of a shallow foundation (both strip and circular) on clay, underpinned by rows of piles either at the centre or at the edge of the foundation. A numerical study has also been carried out for a simple idealised problem of a shallow rigid strip foundation which is upgraded by either width enlargement or underpinned by rows of piles beneath edge.

The finite element method has been used for this analysis, with the soil treated as a two-phase elasto-plastic soil, with both soil failure and consolidation being considered within a single analysis. Solutions have been obtained for the time-settlement behaviour of the foundation after installation of the pile. The influences on this behaviour of pile length, time of installation, and applied load level are examined. Comparison is made between foundation enlargement and installation of the piles, and a study is made of the influences of extra width or pile length, and applied load level on the behaviour of the upgraded foundations.

Laboratory model tests have been carried out to investigate the settlement behaviour of a circular footing underpinned or upgraded by a pile at the centre, and the effect of pile length and load level have been examined. The experimental results are compared with numerical analyses, with laboratory tests being carried out to measure the required engineering soil properties. Some side issues such as creep settlement and electro-osmotic effects are also addressed.

It is found that the effect of the length of the pile becomes more significant at earlier times of pile installation. As would be expected, the rigidity of the foundation has a significant effect on load transfer from the existing foundation to the newly installed piles. The results show that piles installed within a rigid strip foundation are more effective than those installed below a flexible foundation. Also, the earlier that the piles are installed, the less the final settlement, with more load being transferred to the piles.

Comparison between foundation enlargement and underpinning with piles has shown that the piles generally provide the more effective enhancement option, and that beyond a certain extra width, foundation enlargement has no further effect on settlement reduction. Both methods become more effective as the applied load level increases, with underpinning by piles becoming increasingly preferable to foundation enlargement.

The work described in this thesis has been directed ultimately towards the development of a more reliable, but practically useable, approach for the design of piles for underpinning work as well as understanding better the load transfer mechanism from an existing foundation to an upgraded foundation. Such a simplified method has been developed and the formulation is presented. The application of this simplified method to the more accurate numerical solutions and to the experimental results, suggests that it may have applicability in the design of underpinning piles for practical projects.

PATRICK, MARK
SHEAR CONNECTION PERFORMANCE OF PROFILED STEEL SHEETING IN COMPOSITE SLABS
PhD Thesis - Supervisor: A/Professor RQ Bridge

The shear connection performance of profiled steel sheeting which forms the longitudinal tensile reinforcement in the soffit of a composite slab has a major effect on slab behaviour. The primary objective of this thesis is to explain this statement, particularly in relation to ultimate load conditions.

The actions which control the shear connection performance of profiled steel sheeting have to-date been much less well understood than those for deformed reinforcing bar. Perhaps the major achievement of this thesis was to unravel some of the mystery surrounding this subject. It is conclusively shown that mechanical interlock and friction are the primary actions by which certain types of profiled steel sheeting resist longitudinal slip after the breakdown of adhesion bond. Frictional resistance is defined as the component of longitudinal slip resistance affected by a change in the magnitude of the lateral force or pressure acting across the sliding interface. The remainder of the longitudinal slip resistance is mechanical in nature and is unaffected by a change in the lateral force or pressure.

It has been discovered that frictional resistance is concentrated at slab supports, and is proportional to the magnitude of the support reactions and the coefficient of friction developed between the sliding surfaces. A new partial shear connection strength theory has been developed to account for this behaviour which causes the longitudinal slip resistance of a profile to increase as vertical load is applied to a slab. Mechanical resistance is assumed to develop uniformly between the end of the slab and the critical cross-section.

A new small-scale structural test called the Slip Block Test has been developed to determine the shear connection performance of profiled steel sheeting. During the test, longitudinal slip is induced in a small element of a composite slab in a carefully-controlled manner whereby simultaneous estimates for the mechanical interlock and coefficient of friction can be determined at regular intervals of slip. The test set-up closely simulates the conditions which occur at a support where the pans of the sheeting are clamped between the concrete and the supporting member. The results from the Slip Block Test are used directly in the physical model of the new partial shear connection strength theory.

A systematic approach was taken to investigate the accuracy with which the theory can predict the ultimate strength of a series of slabs designed to fail in either flexure or longitudinal slip. For this purpose, comprehensive information about the shear connection performance of the particular profiled steel sheeting used for the slabs was obtained from tests on a large number of slip blocks. The adverse effects of diagonal shear cracking were also taken into account in the analysis.

However, the new partial shear connection strength theory cannot predict the occurrence of vertical shear failures. Another investigation was conducted into the influence that vertical shear had on the flexural capacity of a series of slabs which were designed, using the new theory, to fail in flexure and not by longitudinal slip. The vertical shear failures which occurred in these slabs were by either diagonal splitting or flexure-shear. Since they are the first vertical shear tests on composite slabs to cause failure by shear rather than longitudinal slip, they form a basis on which future investigations of this type can be conducted.

SHORTEN, GRAHAM G
GEOTECHNICAL ANALYSIS OF RECENT ESTUARINE ORGANO-CALCAREOUS SILTS, FIJI
PhD thesis - Supervisor: Professor JP Carter

Estuarine deposits of Holocene organo-calcareous silt provide numerous engineering problems in Fiji, and worldwide. A deposit 25-40 m thick blankets the floor of Suva Harbour and the subsidiary Draunibota Bay, on the southeast coast of Viti Levu. The silt is the latest sedimentary infill over a late Pleistocene erosional surface which is dissected to 50 m below current mean sea level (msl) at the harbour margins, and to at least 90 m further seaward. The distribution of Pleistocene and Holocene sedimentation was strongly influenced by inlets developed on grabens in Mio-Pliocene bedrock. The silt deposit forms part of a transgressive and highstand systems tract related to the latest glacio-eustatic sea level rise, and includes a series of lobate delta deposits currently prograding at the mouths of streams entering the harbour. The deposit was formed in a lagoonal/estuarine environment of restricted circulation in a marginal/back-barrier reef situation and received a variety of marine carbonate and terrigenous sediment contributions, as well as organic substances from both autochthonous and allochthonous sources. Drilling and sampling indicates the silt is homogeneous, nonlayered and thoroughly bioturbated, but a series of seismic reflectors spaced 1-5 m probably indicates periodic influxes of terrigenous material. Acoustic turbidity due to accumulations of biogenic gas over palaeo-channels may well represent zones of high pore fluid pressure, and indicate lower soil strength. The passage of overpressured gas fronts is believed to result in hydraulic fracturing and consequent degassing of the silt. The silt deposit displays a slight upward coarsening in response to shoaling conditions, accompanied by an upward increase in both organic carbon and calcium carbonate proportions, and a decreasing terrigenous contribution. The increase in organic carbon is closely mirrored by increased diagenetic development of bacterially-deposited agglomerates of iron sulfide crystals in the pore spaces. Radiocarbon dates indicate a consistent rate of deposition in the Draunibota palaeo-channel of 4.3 m/1000 yr since the marine transgressive front passed the site some 9,600 yr BP. The dates extend the reliable local sea level data for southeast Viti Levu back some further 4,000 years, and support a contention that sea level reached its current position here at around 4,000-4,500 yr BP, about 2,000 years later than on the coast of southeast Australia. Palaeo-water depth in the Draunibota channel reached a maximum of 20 m some 5,000 yr BP and, subsequently, the sea floor gradually shoaled to its present position just below msl.

A series of investigations at the Cement Works Bridge site has determined consistent insitu shear vane results which are comparable with undrained shear strength results from the static cone penetrometer down to 20 m. Correlation with pocket shear vane tests is equivocal. The estuarine silts are medium to very sensitive. Correlations of various parameters with plasticity index vary markedly from widely accepted norms; attributable in part to increasing quasi-overconsolidation towards the surface. A combination of unusually high friction angle and high plasticity in the silts gives rise to further anomalous correlations. However, there appears to be a good site-specific correlation between normalised undrained shear strength and overconsolidation ratio. The effective friction angle is dependent on confining stress, and high compressibility appears to play a key role in volume reduction during shear and consequently reduced shear strength. The behaviour of the silt is more effectively examined through critical state soil models such as Modified Cam Clay rather than in attempting to establish shear strength parameters through empirical correlations that fail to take full account of volumetric strains and the actual stress state in the soil.

The soil indices and void ratio of the organo-calcareous silts are closely dependent upon organic carbon content. Despite their uniform appearance, lateral and vertical variability of engineering properties is significant, and is a function not only of site physiography but of time-related effects such as palaeo-water depth. The distribution of organo-calcareous silts on Casagrande's plasticity chart reflects changes in the depositional environment, and clearly marks the onset of the influence of prograding deltas. Anomalous void ratio-depth relationships are linked to the variation in organic content. This variation is closely related to the state of evolution of the coastline resulting from the post-glacial marine transgression and stillstand. It may be feasible to determine engineering parameters for these soils from simple measurements of carbon and sulfur, given a knowledge of their depositional history.

Critical state parameters derived from the results of a number of investigations around Viti Levu show there is little variation in the ratio of deviator to mean effective stress at critical state. High friction values are related to angular quartz and feldspar detritus. The range of volumetric strain-effective stress behaviour is much wider; the organo-calcareous silts of Fiji fall into two groups of compressibility behaviour depending on whether the sediments were deposited in more open embayments or in restricted inlets. Volume reduction tends to occur on shear due to the high initial void ratios, so that shear strengths are lower than might otherwise be expected from the friction parameters. High void ratios are attributed to intraparticle spaces in the skeletal carbonates, organic and colloidal structures, remnant gas bubbles, and framboidal aggregates of diagenetic iron sulfide. There appears to be a global correlation linking compression index and void ratio across a wide suite of marine sediments ranging from calcareous sands, through organo-calcareous silts, to pelagic clays and oozes; all having a common genesis in relatively quiet environments. The gross permeability of the deposit deduced from monitoring of embankment settlement is close to that predicted from a simple model of soil structure, but about five times higher than measured laboratory values.

Creep is implicated in long term settlement. Although the geological history indicates the deposits should be normally consolidated throughout, the organo-calcareous silts of Fiji are typically quasi-overconsolidated in the upper third of the deposit. The increasing apparent overconsolidation towards the surface is contrary to what might be expected if delayed compression was the only process operating. Oedometer tests extending over 7 months indicate the rate of volume change due to creep follows the Singh-Mitchell relationship, but assessment of creep from radiocarbon dates suggests that the very long-term rate is higher than might be expected. Creep appears to be stress-dependent, at least at lower test pressures, in common with other marine sediments.

A serious failure in the approach embankment of the Cement Works Bridge was originally blamed on a variety of external factors. The construction situation was re-analysed using a finite element algorithm in which the silt deposit was modelled as a Modified Cam Clay material, utilising the representative set of critical state parameters established in this study. The computer model predictions agree well with records of the events during construction and accurately represent the timing and location of failure. Moreover, the model predicts that failure of the embankment and adjacent bridge abutment would have occurred regardless of external factors, as the combination alone of construction sequence, foundation geometry, and subsurface processes and material parameters was sufficient to initiate failure. The analysis indicates that uncertainties identified in the adopted material parameters for this material would lead to only small differences in predicted settlement and would have little effect on the timing of the initiation of failure. Successful prediction of longer term settlement in fine-grained organic sediments requires incorporation of creep effects.

SMEDLEY, DELWYN
SNOWDRIFTING AROUND ANTARCTIC BUILDINGS
Master of Engineering (Research) Thesis - Supervisor: A/Professor KCS Kwok

Antarctic buildings suffer from a variety of problems due to snowdrifting, ranging from inconvenience caused by blocked doors and windows to complete inundation necessitating abandonment. In this study, wind tunnel testing is used to investigate the effect of building design on snowdrift accumulation and to propose building guidelines for the minimisation of snowdrifting problems in Antarctica.

Antarctic snowdrifting was simulated in a purpose-built Snowdrift Wind Tunnel (S.W.T.) using sodium bicarbonate as the model snow particle. Without the model snow present, the turbulent boundary layer flow in the S.W.T. was found to closely resemble that over a typical coastal Antarctic site during the summer months at a nominal scale of 1/50. When the model snow was introduced, the flow was found to give a good simulation of f low over such a site in the winter months at a similar scale. The S.W.T. simulation was found to satisfy most of the important similarity criteria proposed by other researchers.

The first series of tests were performed on a series of 1/50 scale models of small to medium sized modular buildings. The tests were designed to investigate the effect of varying the width, height and length dimensions of the buildings in both on-ground and elevated configurations. The results were used to formulate a set of guidelines for Antarctic building designers to minimise snowdrift accumulation.

The second series of tests were carried out on groups of three identical 1/50 scale models. The tests were designed to investigate the effects of varying the spacing between the buildings and the relative height dimension of the buildings in both the on-ground and elevated configurations. These results were also used to form a set of guidelines for the arrangement of groups of buildings to minimise snowdrifting problems.

Lastly, the S.W.T. was used to investigate a known snowdrifting problem around the workshop building at Davis Station, Antarctica. A 1/100 scale model of the workshop building was tested in its existing condition and also with two roof attachments designed to reduce and reposition the snowdrift away from the building wall. One of the attachments was successful at repositioning the snowdrift, but neither attachment gave a reduction in snowdrift volume. Although it was not considered that an optimal solution was found to the snowdrifting problem around the Davis workshop, this series of tests demonstrated the usefulness of the S.W.T. as a tool for investigating and remedying existing snowdrifting problems in Antarctica.

THOMSEN, NIELS B
WEAR STUDIES OF CERAMIC MATERIALS UNDER CONTACT LOADING
PhD Thesis - Supervisor: Professor BL Karihaloo

The importance of wear in modern high technology devices has made it imperative to develop new materials with improved wear performance and to improve models for predicting their wear characteristics.

One novel group of high technology materials with promising wear characteristics is ceramics. Ceramics have high hardness, temperature resistance and chemical stability which are all desirable and beneficial for high wear resistance. However, they have relatively poor resistance against cracking, i.e. low fracture toughness.

There is one type of ceramics, though in which the low fracture toughness problem has been partially overcome, namely zirconia-based ceramics. The improved toughness of zirconia ceramics is mainly attributed to the phase transformation of tetragonal zirconia to monoclinic crystalline form under high stresses. This phase transformation leads to toughening which is called the "transformation toughening". The transformation toughening of zirconia ceramics and its role in the rolling and sliding wear process forms the main topic of this thesis.

The exposition begins with an overview of the current state of research into the modelling of wear, strengthening and toughening of ceramics, as well as of the experimental observations of wear in zirconia ceramics.

The wearing surface in rolling and sliding wear is approximated by a half-plane subjected to a frictional contact load. Under such loading inherent flaws, such as microcracks, voids and inhomogeneities eventually develop into macrocracks with a resultant deterioration in wear performance. Two macrocrack configurations are studied. A straight edge crack perpendicular to the surface and a straight subsurface crack parallel to the surface. The cracks are modelled using the dislocation formalism, and the contact load is assumed to be Hertzian. In the vicinity of the crack tips, where a high tensile stress field is anticipated, the material is allowed to undergo an irreversible phase transformation in accordance with an appropriate transformation criterion. The transformation zone around the crack tip (or tips) is modelled as a collection of minute circular regions. Such a model is assumed to be a good representation of the transformable precipitates e.g. in partially stabilised zirconia. The shape and size of the transformation zone at the crack tip(s) change continuously with the position of the contact loading. The stress/strain field from the transformation zone is obtained by applying the Eshelby formalism.

An extensive analysis is performed for the purely elastic material behaviour and the results complement those available in the literature. The phase transformation exerts a strong influence upon the behaviour of the cracked material compared to the purely elastic material through the significant closing effect on the crack faces. For cracks near the surface, this results in the mode I stress intensity factor being almost zero. However, as the transformation zone is highly asymmetric relative to the crack faces because of the non-uniform stress field due to the applied contact load, the mode II loading of the crack tip(s) can be severely enhanced. This results in high residual near tip deformations after unloading, i.e. high residual mode II stress intensity factor.

Dilatational and deviatoric strains accompanying phase transformation near the contact lead to the material heaving, so that an initially flat surface becomes progressively more "wavy" as the contact loading passes over it. This has ramification for the sliding wear more characteristics of the material. Zirconia ceramics have shown promising wear properties in a number of applications. However, in certain load configurations their wear performance is very poor. The reason for this is believed to be subsurface phase transformation. To study this, the surface uplift due to transformation of a circular inclusion and an infinite array of inclusions in half-plane is analysed, and compared to an uplift analysis of a transformable spherical inclusion in half-space. The transformation strains have significant effect on the surface topography with resulting deterioration in the rolling and sliding wear characteristics of the surface. The two-dimensional approximation is shown to overestimate the surface uplift by up to three times that predicted by the more realistic three-dimensional model. The results indicate that the surface topography is considerably altered by the occurrence of transformation in the near surface area, and in particular by the deviatoric strains associated with it.

The volume expansion accompanying phase transformation of precipitates located immediately beneath the contacting surface induce a surface uplift leading to surface waviness and altered rolling and sliding conditions. The very same precipitates on the other hand enhance the toughness of the ceramic by preventing the growth of surface cracks. In order to find a compromise solution, an optimisation problem is formulated for an idealised model consisting of an edge crack normal to the contacting surface and a periodic distribution of transformable grains in the layer immediately beneath this surface. The objective is to maximise the crack tip shielding (i.e. transformation toughening) by varying the volume fraction and the size of the layer without exceeding a prescribed allowable surface uplift. It is shown that the maximum volume fraction of tetragonal zirconia is attained at a certain depth below the surface, but that its magnitude is considerably smaller than that pertaining in peak-aged partially stabilised zirconia currently being manufactured.

WALLACE, STEPHANIE
THE RELATIONSHIP BETWEEN OCEAN WAVE STATISTICS AND SATELLITE MEASUREMENTS
Master of Engineering (Research) Thesis - Supervisor: Dr R Coleman and Dr ISF Jones

Wave statistics are the basis of offshore and coastal designs. Engineers rely on these parameters to estimate extreme waveheights which are the cause of structural damage and shipping disasters. Satellites are the tools of the future, particularly in the study of the oceans, as no other instruments are capable of providing extensive continuous global coverage over such a vast region.

The predominant aim of this thesis is to analyse temporal wave statistics and to determine if these measurements are applicable to spatial waveheight measurements made from satellite altimeters. This was approached by examining waveheight measurements using several statistical properties of samples over both time and space.

Time series recordings of waveheights were made with sonic wave gauges at two platforms in Bass Strait, together with the permanent Weather Station system. The variability of waveheights over both time and space was examined using the three instruments, and was found to demonstrate significant waveheight (H_S) fluctuations despite relatively steady conditions. Probability distributions, which are the foremost method for describing the sea surface, were then applied to the temporal waveheight files to see which were the most suitable for maxima and waveheight prediction.

Temporal correlations were made from continuous waveheight measurements obtained from the Weather Station and its predecessor instrument, the Baylor Wave Gauge. These curves were then compared with spatial correlations drawn from the GEOSAT satellite H_S values, and the two statistics were found to be in good agreement.

Groups of high waves were examined in the temporal waveheight files using the envelope theory. The average number of waves per group were found to vary considerably in a 1024 second file, and a wave age dependency was evident. The propagation of the wave groups was then considered to see if a similar measurement would be found in the spatial instantaneous footprint of the altimeter.

In order to directly compare temporally and spatially derived ocean parameters (other than H_S it is necessary to know how many waves are contained in the altimeter footprint. This can be estimated if the crestlength and wavelength are known. Therefore the relationship between these two parameters and wave age (which may also affect crestlength) were examined, and crestlength was found to vary under different conditions and seas of different ages.

XIAO, BO
NUMERICAL SIMULATION OF DEEP EXCAVATIONS IN ROCK MASSES
PhD thesis - Supervisor: Professor JP Carter

Deep excavations are widely used for various purposes in industries including civil, mining, military, petroleum, energy and environmental engineering. The number and size of excavations have increased steadily in recent years. In engineering practice, designers are particularly interesting in making accurate predictions of the magnitudes of movements in the surrounding rock masses associated with the construction activities, and the likely extent of damage to adjacent structures and facilities. It is therefore of interest to develop reliable and efficient techniques which are able to predict accurately the deformation and stress distributions around excavations in the rock masses. On the basis of both theoretical and practical considerations, this thesis attempted to develop efficient techniques for analysis and to provide a better understanding of the rock mass behaviour during excavation.

Rock masses are seldom found in nature without joints or discontinuities which can have a significant effect on the gross mechanical response. In practice, it is almost impossible to explore all of the joint systems or to investigate all their mechanical characteristics. Moreover, when the spacing between the joints is small in comparison with the length scale of interest (such as tunnel width or foundation size), a simulation incorporating the jointing explicitly is very difficult and costly to implement. In these cases, the use of the equivalent continuum model to simulate behaviour of jointed rock masses could be valuable. A concept of "deformation equivalence" has been adopted to derive an equivalent continuum model for simulation of elastic behaviour of jointed rock mass. At higher levels of applied stress either the intact rock or some of the joints or both may yield, and subsequently they will behave plastically. An elastoplastic equivalent continuum model containing any finite number of joint sets in which any of the joint sets and the surrounding intact rock may undergo plastic deformation has been described.

A quadratic boundary element method for an anisotropic medium has been developed. It has been demonstrated that the use of quadratic elements can yield accurate results with relatively coarse boundary element meshes, and can not only more adequately represent a curved boundary but it can also give more accurate results than constant elements.

A coupled finite element and boundary element method for analysis of boundary value problems in anisotropic rock masses has been developed. This method is characterised by using equivalent continuum models to represent the rock mass as an equivalent, anisotropic, elastic or elastoplastic continuum. In this method, the presence of joints, the sequential excavation or construction, inhomogeneous materials, material non-linearities can be considered in regions of interest which can be represented numerically by a finite element mesh, and the boundary discretisation can be used to represent the response of anisotropic rock masses in the far field. The formulation has been validated by comparing available analytical solutions.

In order to provide a detailed understanding, of the behaviour of a jointed rock mass around excavations, numerical studies for both circular openings and deep basements excavated in jointed rock masses have been carried out. For circular openings, the predictions illustrate the effects of joint spacing and shear stiffness on the ground response curve, and the zones in the rock mass around the tunnel where intact rock has yielded plastically and where the joints have yielded in shear or have opened. Plots of the dimensionless ground response curves, the vectors of displacement and the contours of the yield ratio for tunnels at various dimensionless depths in jointed rock masses have been presented. For basement excavation problems, the numerical results illustrate the effects of anisotropy of the rock mass and the orientation and spacing of the joint sets around the excavation. The deformation and stress distributions the stability of rock masses around the basements and effect of dilatancy in rock joints on the movements of the rock mass have been studied.

A case history of a basement excavation adjacent to railway tunnels in rock masses is also presented to demonstrate the capability of the proposed method in solving practical problems. The excavation is located in the central business district of Sydney and is approximately 30m deep with a total of about 500,000m³ of rock having been excavated. Good agreement has been found between the field measurements and numerical predictions.

YEUNG, STEVE
DESIGN OF COMPOSITE COLUMNS
Master of Engineering (Research) Thesis - Supervisor: A/Professor RQ Bridge

The new Australian Standard for composite construction will incorporate the findings of recent research on composite structures, and present them in the limit state format, which is gradually replacing the working stress method in many structural design codes. Several aspects in regard to the design of composite columns have been investigated in this work. The results of these investigations will be used in the preparation of the new code.

A review was made on three current methods of short column length calculation. These are the methods by Young (1973), Rotter (1982) and Bridge (1987). This was followed by an extensive parametric study to critically examine the applicability of Bridge's method for a range of cross-section types, slenderness rations, initial imperfections, load eccentricities and ratios of applied end moments. The objective was to derive a conservative empirical expression for determining the short column length, below which a column can be designed for its cross-section strength without the need to consider the slenderness effects. The results of the study showed that the linear expression developed by Bridge gave a good approximation to the short column length.

The provisions of Eurocode 4-1990 and AS 3600-1988 for the capacity of a column subject to combined axial compression and bending have been evaluated by performing a parametric study for a range of cross-sections and slenderness ratios.

Accurate estimates of the capacities of the same columns were obtained from inelastic buckling analyses, and were compared with those from Eurocode 4 and AS 3600. Eurocode 4 gave slightly more accurate predictions for column strength.

Recommendations on design details are made in the light of a review of five current design codes for composite columns and the results of a number of recent research Projects.

ZHANG, WEI JIAN
TORSIONAL RESPONSE AND INTERFERENCE EFFECTS OF WIND-EXCITED TALL BUILDINGS
Master of Engineering (Research) Thesis - Supervisor: Associate Professor KCS Kwok

This thesis presents the results of a study of torsional response and interference effects of wind-excited tall buildings through wind tunnel model tests.

Wind tunnel model tests were carried out on a tall square cross-section building model with and without structural eccentricity in both open country and city centre terrains by using an aeroelastic test rig designed for pure torsional vibration interference effects from neighbouring building models of different sizes and shapes on torsional response and excitation of tall buildings were extensively investigated by locating four types of interfering models upstream and downstream of the centric and eccentric principal building models. Torsional excitation spectrum, distribution of peak response and aerodynamic damping were examined to determine torsional response and excitation characteristics.

In the case of an isolated building, it was found that the torsional response of the tall square building can be substantially enhanced when structural eccentricity exists between the elastic and geometric centres. For a 10% geometrically eccentric ratio and for the open country terrain, there was a significant increase of maximum mean response by a factor of up to 3. Unstable lock-in type torsional vibration due to vortex shedding was observed for the eccentric building at a structural damping of 1% of critical damping and at + 90º position, in which large amplitude twist angular displacement occurred. Increase in turbulence associated with the city terrain, however, effectively mitigated torsional lock-in excitation.

The maximum mean torsional response of the isolated centric and eccentric buildings can be enhanced up to a factor of 1.2 due to the presence of the interfering buildings in the open country terrain. However, for most positions of the interfering buildings, the mean torsional response of the principal buildings was reduced because of shielding effect of the interfering buildings. When the frequency of vortex shedding from an upstream interfering building coincided with the natural frequency of the principal building and the shed vortices impacted the principal building during their propagation, torsional resonant buffeting occurred and dynamic torsional response was increased by a factor of 2 or more for the centric principal building a (without structural eccentricity), and by a factor of up to 4.6 for the eccentric principal building. The critical location of an interfering building and critical reduced velocity which result in resonant buffeting depend on the size and shape of the interfering building as well as the natural frequency and eccentric position of the principal building relative to wind incidence. Of particular concern is that resonant buffeting can occur at lower reduced velocities consistent with normal strong wind conditions commonly encountered in practice. On the contrary the interference effect from a downstream building mostly reduced dynamic torsional response of the principal building, except for a few positions which produced increase in response of about 20%. The high turbulence flow associated with the city terrain greatly reduced dynamic interference effects, and no significant torsional resonant buffeting was found around the critical locations which were found in the case of the open country terrain.

The University of Sydney - Civil Engineering

1996 Higher Degree Theses