Thesis--Ph. D., University of Hong Kong. / Mimeographed.

Thesis (M.A.)--University of Hong Kong, 1972. / Typewritten.

Thesis (Ph. D.)--University of Oklahoma, 1990. / Includes bibliographical references (leaves 284-293).

Thesis (Ph. D.)--University of Hong Kong, 2002. / Map in pocket. Includes bibliographical references (leaves 306-329).

The work described in this thesis involved the prediction and back-analysis of ground movements and pore water pressures around a temporary excavation, lOm deep, 105m long and 35m wide (50m long and lOm wide at its base) in the heavily overconsolidated Oxford Clay. An experimental programme was carried out which was designed to investigate the nonlinearity and the anisotropy in the soil's response. A series of computer controlled triaxial stress path tests were carried out on specimens of Oxford Clay trimmed from block samples. The initial anisotropic stress state resulted in a highly stress path dependent stiffness, and the stressstrain behaviour was closely linked to the time at which the specimen had been held at constant stress prior to a change in loading. In the triaxial apparatus, shear wave propagation tests using square wave input functions into bender element apparatus were significantly affected by near-field effects and by additional wave components. Tests carried out using sine wave inputs provided a far more consistent output allowing correlation analyses and easier visual identification of the travelling shear wave. The shear modulus of the soil at very small strains could then be determined. A stress path dependent, non-linear, cross-anisotropic elastic model was developed and implemented into the finite element program CRISP. A genuine prediction of the Elstow excavation was carried out while the instrumentation data from the site investigation were temporarily withheld. It was found that the horizontal displacements were modelled satisfactorily but that the vertical displacements were in error by as much as 2 or 3 times. This discrepancy was attributed to volumetric changes suggested by the instrumentation data. A parametric analysis was carried out in which the effects of the initial stress state, the degree of anisotropy, and the degree of non-linearity were investigated. This showed that although it was possible to improve the accuracy of the prediction locally, it was not possible to improve on the overall pattern of behaviour predicted by the first non-linear cross-anisotropic analysis.

This thesis details the results of an investigation into a technique for determination of "useful" structural parameters from forced vibration testing. The implementation of this technique to full scale civil engineering structures was achieved by several developments in the experimental and computational fronts: a vibration generator and a computer-aided-testing system for the former and two computational algorithms for the latter. The experimental developments are instrumental to exciting large structures and acquisition of large quantities of useful data in digital format. These data serve as inputs to the computational algorithms whose outputs are structural parameters. These parameters are in either modal or spatial forms which cannot be measured directly but have to be extracted from the raw data. The modal-parameter-extraction method is based on direct Least-Square fitting technique and is simple to implement. The technique can yield good accuracy if the residual effects from out-of-range modes are removed from the raw data before fitting. The spatial-parameter- extraction method distinguishes itself from other conventional methods in the way that the orthogonality property is not explicitly used. This method is applicable to situations where conventional methods are not; i.e. in cases if modal matrices are not square. Some success was achieved in cases in which computer synthesized or good quality laboratory test data were used. Full scale field tests of a tall office block and a slender tower were carried out and their modal models obtained. Attempts to obtain spatial models of these structures were not carried out, however, as this task can be a separate research topic in its own right. Further research in such application is still required.

No description available.

Fatigue crack propagation rates have been measured for two titaniumbased aeroengine disc alloys using compact tension test pieces. The loading block employed simulates two features of the engine flight pattern. A major stress cycle represents the start-stop operation which leads to low cycle fatigue. In-flight vibrations, which may give rise to high cycle fatigue, are represented by superimposed minor cycles of high frequency. This combined loading is applied in a specially developed test facility consisting of an electromagnetic vibrator mounted above a servohydrau1ic actuator. When the minor cycles are inactive the fractographic cracking processes are those associated with major cycle crack growth. Once active, the minor cycle growth may either generate extensive cyclic cleavage or increase the separation of the fatigue striations associated with the periodic major cycles. The contribution of the minor cycles to the total growth rate is dependent on their relative number and size. In gas turbine and compressor discs and blades, components which experience large numbers of minor cycles per flight, the damage associated with active minor cycles is dominant. Consequently, the onset of minor cycle damage effectively determines the useful life of such components. The threshold values associated with the minor cycles have been used to predict the onset of minor cycle activity. Similarly the method of linear superposition has been used to predict the subsequent fatigue crack growth rates. These predictions are successful for Ti-6Al-4V, whilst for Ti-5331S they are either found to be accurate or safe. Although Ti-5331S displays a marginally greater resistance to the onset of minor cycle crack growth, of greater significance is its reduced crack growth rates prior to this event. As a consequence components fabricated from Ti-5331S will exhibit longer fatigue crack propagation lives when subjected to the conjoint action of high and low cycle fatigue.

The structural behaviour of single shear bolted connections, double shear bolted connections and single shear screwed connections of thin sheet steels at elevated temperatures has been investigated in this study. The current design rules on bolted and screwed connections of thin sheet steels for cold-formed steel structures are applicable for ambient temperature condition only. These design rules may not be applicable for elevated temperature conditions. Therefore, design guidelines should be prepared for bolted and screwed connections of cold-formed steel structures at elevated temperatures. A total of 30 tensile coupon tests were conducted to investigate the material deterioration of the thin sheet steels at elevated temperatures, and also to determine the critical temperatures for connection tests. A total of 510 tests on single shear bolted connections, double shear bolted connections and single shear screwed connections of thin sheet steels at elevated temperatures was performed in the temperature ranged from 22 to 900?C using both steady state and transient state test methods. The test results were compared with the predicted values calculated from the North American, Australian/New Zealand and European specifications for coldformed steel structures. In calculating the nominal strengths of the connections, the reduced material properties of the thin sheet steels were used due to the deterioration of material at elevated temperatures. It is shown that the design strengths predicted by these specifications are generally conservative at elevated temperatures. Finite element models for single shear bolted connections, double shear bolted connections and single shear screwed connections were developed and verified against the experimental results. Explicit dynamic analysis technique was used in the numerical analyses. Extensive parametric studies that included 490 finite element specimens were carried out using the verified finite element models to evaluate the bearing strengths of bolted connections as well as the tilting and bearing strengths of screwed connections of thin sheet steels at elevated temperatures. Design equations for bearing strengths of bolted connections as well as design equations for tilting and bearing strengths of screwed connections were proposed based on both the experimental and the numerical results in the temperature ranged from 22 to 900?C. The bearing strengths of bolted connections as well as the tilting and bearing strengths of screwed connections obtained from the test specimens and the finite element analyses were compared with the predicted strengths calculated using the proposed design equations and also compared with the design strengths calculated using the current North American, Australian/New Zealand and European specifications with consideration of the reduced material properties at elevated temperatures. It is shown that the proposed design equations are generally more accurate and reliable in predicting the bearing strengths of bolted connections as well as the tilting and bearing strengths of screwed connections of thin sheet steels at elevated temperatures than the current design rules. The reliability of the current and proposed design rules was evaluated using reliability analysis. The proposed design equations are suitable for bolted and screwed connections assembled using thin sheet steels of thickness ranged from 0.35 to 3.20mm. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

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