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.

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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 behaviour of very slender eccentrically loaded reinforced concrete columns is investigated, both analytically and experimentally, under short-term and sustained loading. Short-term loading investigations involved the testing of thirty-six columns having slenderness ratios between 28.85 and 57.69. The first twenty-four columns were cast with a concrete having a mean 28 day cube strength of 46 •. 82 N/mm2 and subjected to loading at eccentricities of 10mm and l5mm. The remaining twelve columns were cast with a concrete having a mean 28 day cube strength of 34.69 N/mm 2 and loaded at an eccentricity of l5mm. The behaviour of four columns cast with the stronger of the two concretes was monitored under sustained loading for a period of about eighteen months. These columns had slenderness ratios of 38.46 and 48.08 and loads were applied at eccentricities of 10mm and l5mm. An analytical procedure based on the classical equations of mechanics (equilibrium compatibility and properties of the constituents) has been developed to predict the behaviour of slender columns under an eccentric load. Comparisons between the observed and analytical behaviour of forty columns, indicate that the proposed analysis estimates closely the load capacity and load deformation behaviour of very slender reinforced concrete columns. The validity of the proposed method has also been demonstrated in extensive comparisons between predicted and experimental observations obtained from tests performed by other investigators on very slender columns. The design of very slender columns in accordance with CPllO is based on the assUmption that failure would occur when the maximum concrete compressive strain reaches an ultimate value of 0.0035. In tests this assumption has proven to be wrong as instability occurs at very low concrete strains, normally no more than 0.001. Thus the code mentiqned is incorrect in using a theory based on material failure· for very slender columns. The results of analytical studies into the behaviour of slender columns under sustained loading indicate that the present provisions in CPllO do not account fully for creep effects. As a consequence the recommendations of CPllO lead to unconservative designs. The recommendations of ACI318 on the other hand, agree in general with the analytical results.

Slender reinforced concrete columns have become widely used as structural members in recent years. Current Codes of Practice for Structural Concrete lack sufficient guidance to designers for their safe and efficient design. This investigation studies the behaviour of very slender, pin-ended, reinforced concrete columns, under short-term and sustained loads, by experiment and theoretical analysis. A new approach is used in the method of applying load to the column. A concentric axial load and independant primary end moments are considered. This allows the determination of secon~ary moments due to axial force and secondary deflections to be easily determined compared with the conventional eccentric load methods adopted in the past. A non-linear, second-order computer analysis has been developed which is capable of accurately predicting the deflections of hinged columns throughout the loading range from zero load to buckling failure, for any combination of eccentric loads and primary moments for short or sustained periods. It has the potential to accept end restraint in order to model framed columns. An extensive experimental programme of tests has been performed on 48 column specimens with slenderness ratios between 29 and 59 under short term loads and 5 specimens under sustained loads for up to two years. A total of 68 short column specimens with an identical section to the slender columns and material specimens were also tested. The specimens had a mean wet-cured cube strength of 42 N/sq.mm. The results of these tests and, 120 similar results of other authors, confirmed the validity of the proposed theoretical analysis and the assumptions used. The computer program which is presented could be made available to design offices for use on a basic micro-computer. The design methods recommended by three Codes of Practice, CPII0:1972, ACI318:1977 and CPl14:1957, have been compared with the experimental and theoretical results of this work. CPII0 and ACI318 are shown to give conservative designs, with an overall load factor of 3.0 and 2.4 respectively, for design loads compared with the 25 year load given by the proposed theory. CPl14 gives design loads with an equivalent load factor of 1.35. These codes provide conservative designs, but CPII0, unlike ACI318, does not recommend the use of a second-order analysis or highlight the potential dangers of long-term distress due to creep deflections in slender columns. An alternative method of design to the current codes for slender columns is presented in the form of load moment interaction curves for buckling rather than material failure. These show both primary and secondary moments, and buckling loads for any slenderness ratio. The criterion of material failure at an ultimate compressive strain of 0.35% (CPII0) or 0.30% (ACI318) is shown to be incorrect when column failure occurs by buckling rather than compression. The observed compressive strain at failure of columns with slenderness ratios between 29 and 59 in this work was typically 0.1%.

Theoretical and experimental investigations into the compressive buckling behaviour of unidirectional CFRP thin- walled channel sections subject to built-in end conditions are described. Local and overall modes of instability are considered and the effects of transverse shear on both modes are discussed. Particular emphasis is given to the development of local instability theory for orthotropic materials and the basis for design charts for a range of thin-walled orthotropic sections is included. These analytical developments are accompanied by an investigation of numerical methods in which a finite difference technique is applied to single orthotropic plates and a finite element programme is used with multi-plate sections. Good correlation is observed between analytically and numerically derived buckling loads. Buckling analyses are confined to classical linearised theories and the sensitivities to eccentric loading, applied end moments, and imperfect end restraints are demonstrated. The pultrusion process for manufacture of continuous unidirectional CFRP thin-walled sections is described and suggestions for its development to multidirectional composites are given. Test, methods for the measurement of the principal mechanical properties of unidirectional CFRP from, in some cases, small specimens are detailed. Measured properties are shown to correlate with fibre volume fractions obtained from areal analyses of polished sections. The design of a strain, gauge bridge amplifier and data logging system utilised during column testing is included. The Southwell method is shown to be applicable to flexural and torsional-flexural buckling modes and in general measured buckling loads fall short of theory by 50%. Local buckling loads are indistinct although buckled forms correspond to theoretical predictions and little post buckling strength is observed. A theoretically derived buckling chart for unidirectional CFRP channel sections is presented and a minimum design safety factor of 2 is recommended.

This thesis is divided into two parts, Part A deals with the measurement and analysis of wave pressures on real seawalls and Part B deals with the resulting structural response of these seawalls. There have been only thirteen previous investigations to measure full scale wave impact pressures on coastal structures, and of these only five were conducted with sensitive electronic measuring equipment. The infrequent occurrence of impact pressures in a real sea has meant very little impact pressure data has been collected by these previous investigations. This investigation is the first of its kind to be carried out in the U.K. losing modern measuring, and recording equipment, the volume of wave impact data obtained (over 150 impacts recorded) is significantly greater than the combined results of all previous full scale investigations. The magnitude of the wave impacts measured during this investigation were generally lower than those measured by other investigations, the-maximum impact pressure being of the order of seven times the hydrostatic pressure. The pressures measured were found not to fit any current equations. The data has also shown that impact pressures can occur simultaneously over large areas and are not just localised events as previously thought. The most important parameter in the generation of wave impact pressures in a real sea was found to be the percentage of air entrained in the breaking wave. None of the equations currently in use for estimating wave impact pressures consider this parameter, which probably explains why these equations do not fit the measured data. An explicit equation for estimating the maximum impact pressure was not found but a method is given whereby -the impact pressure is related to local wave parameters including a coefficient based on the percentage air entrainment. Finite element modelling of the seawalls has shown that impact pressures can cause a significant dynamic response in the seawalls although short duration impacts (as measured in most model studies) have a negligible effect on response.

The dynamic shear response and failure of structural elements under transverse impact loads are studied in the present work. The dynamic shear response is one of the important response modes in structural elements under transverse impact loads, which may lead to various shear failures depending on the loading rates and intensities. Transverse shear localization phenomena, which are represented by a shear hinge, have been observed in several structural elements when subjected to transverse dynamic loading and are studied in this thesis. The features of a stationary shear hinge are illustrated using a rigid, perfectly plastic simplification. The dimensions of a shear hinge for several structural elements are estimated both theoretically and numerically. It is shown that there exists a fixed shear hinge length for a given two-dimensional structural element. The length of a shear hinge is determined by its bending and shearing properties which can be obtained from a quasi-static analysis. When the shear hinge length has been determined, the conventional rigid-plastic method can be used to calculate the shear strain and shear strain rate within the shear hinge during the shear response phase. These theoretical results are employed to model Menkes and Opat' s beam problem to find two possible failure mechanisms, i.e., ductile shear failure and adiabatic shear failure and the associated transition conditions. A double-shear beam(DSB) subjected to a transverse projectile impact is studied experimentally and numerically in order to provide a more fundamental understanding on the features of structural failure in a localised shear zone. Both ductile tensile failure and adiabatic shear banding failure are found in the shear notch section. An analytical model and FEM simulation are developed to predict the DSB response and failures. The theoretical background of the strain energy density failure criterion is discussed and verified in this problem. Among the failure criteria examined in the current study, the strain energy density failure criterion is observed to give reasonable predictions for the failure initiation.

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy