Thesis (M. Phil.)--University of Hong Kong, 1987.

Thesis--M. Phil., University of Hong Kong.

Thesis--M. Phil., University of Hong Kong. / Mimeographed.

Thesis (M. Sc.)--University of Hong Kong, 1960. / Mimeographed. Includes bibliographical references (p. 106-108). Also available on microfilm.

published_or_final_version / Civil Engineering / Master / Master of Philosophy

published_or_final_version / Applied Geosciences / Master / Master of Science

Not available / text

In this dissertation, first the experimental and theoretical observations on the deformational characteristics of brittle geomaterials are reviewed and discussed. A basic conclusion is that special features such as strain softening can not be considered as true material (continuum) properties. These conclusions created a renewed emphasis on the constitutive modelling of such materials. A model that accounts for structural changes is developed. Such changes are incorporated in the theory through a tensor form of a damage variable. It is shown subsequently that formation of damage is responsible for the degradation in strength (softening) observed in experiments, for the degradation of the elastic shear modulus and for mechanical, damage induced anisotropy. A generalized plasticity model is incorporated for the so-called topical or continuum part of the behavior, whereas the damage part is represented by the so-called stress-relieved behavior. The question of uniqueness in the strain-softening regime is examined. It is shown that the constitutive equations lead to a unique solution for the case of rate dependent as well as rate independent formulation. Its implementation in finite element analysis shows mesh size insensitivity in the hardening and softening regimes. The general order of bifurcation of differential equations is employed in order to study the effect of damage accumulation on formation of narrow, so-called shear bands. It is shown that as the damage accumulates, the material approaches localization of deformation. The theory of mixtures is employed for further theoretical establishment of the proposed model. Energy considerations show the equivalence of the two-component damage body to an elastoplastic body containing cracks; the equivalence is considered in the Griffith sense. The mechanisms of failure are considered and discussed with respect to multiaxial stress pads. An explanation of failure, at the micro level, is given. The material constants involved in the theory are identified and determined from available experimental data. The model is then verified by back-predicting the observed behavior.

Analytical and experimental studies were made to develop design procedures for steel gusset plate connections in diagonally braced frames. Stiffness and strength models of structural fasteners based on physical tests were incorporated into inelastic finite element analyses. The modeling techniques were verified by comparing analytical and experimental results of full scale connection tests. Finite element models of bracing connections were generated to determine gusset plate force, stress, strain, and displacement distributions for a variety of connection designs including K-bracing and X-bracing. Based on these results current design procedures were scrutinized and new design procedures were proposed for predicting the tensile strength, buckling strength, and force distributions for bracing connections. Additionally, it was found that gusseted beam-to-column connections are rigid (AISC Type I) and the centroidal axes of the brace, beam, and column members do not necessarily need to intersect at a common working point.

The general problem of an anticrack, present in a simple domain and subject to general remote loading is solved using distributed line forces, acting as strain nuclei, along the line of the anticrack. Subsequently, both dislocations and point forces are used as strain nuclei to achieve mixed boundary value conditions. The influence function for a pair of forces applied to the faces of a semi-infinite notch is found and finally this is used to find the true closure length and interfacial contact pressure. When a sharp-edged indenter is pressed into a half plane material in the half-plane is displaced and 'laps around' the edges of the punch, possibly making contact with the side faces. This phenomenon is quantified within (coupled) half-plane theory, and applied first to an idealised indenter having the cross section of a trapezium, and then to a semi-infinite indenter. The latter allows an asymptotic form to be found which, through a generalised stress intensity factor may be collocated into the edge of any notionally sharp-edged indentation problem. The effect of surface strains on the local slip angle, when an infinite cylinder is slid skew-wise across an elastically similar half-plane is found. It is shown that local frictional orthogonality is not completely consistent with global orthogonality. The problems of a square-ended and an almost square-ended rigid punch sliding with both plane and anti-plane velocity components are studied. It is shown that, for a truly complete contact, if the contacting body is incompressible, convection effects are absent. Introducing either: (a) local rounding or (b) finite compressibility of the contacting body into the problem introduces convection, giving rise to an inconsistency between the global and local requirement of the orthogonal friction law. The state of stress in a three-quarter-plane undergoing antiplane shear deformation is studied, due to the presence of a screw dislocation along one of the projection lines extending from the free surfaces. A simple, accurate formula for the state of stress along the line is found, providing a useful kernel for the solution of crack and contact edge slip problems. The state of stress induced in an axi-symmetric solid formed from a half-space and a bonded semi-infinite rod, by a family of ring dislocations of arbitrary Burgers vector is found. Particular care is given to the interaction between the Cauchy singularity near the dislocation core and the geometric singularity at the rod/half-space junction. Torsional contact between a semi-infinite elastic rod with square ends and an elastically similar half-space was then solved using the ring dislocations as influence functions. This provides an excellent illustration of the imposition of orthogonality condition for a complete contact.