published_or_final_version / Civil Engineering / Master / Master of Science in Engineering

published_or_final_version / Mechanical Engineering / Master / Master of Science in Engineering

published_or_final_version / Civil Engineering / Master / Master of Philosophy

published_or_final_version / Civil Engineering / Master / Master of Philosophy

The interface normal behavior between Ottawa sand and concrete for static and cyclic loading has been studied using Cyclic Multi Degree-of-Freedom test device. The static force controlled test for the interface showed exponential relation between normal stress and strain during initial loading, hyperbolic relation during unloading and linear relation during reloading. A series of cyclic force controlled interface tests are described for normal behavior and the interface behavior is found to be a function of the applied initial normal stress, the amplitude of the stress and the number of loading cycles. The reloading modulus is shown to increase with number of loading cycle. Also, a series of combined normal (force controlled) and shear (displacement controlled) tests are described in which the shear stress for given amplitude of shear displacement is found to increase as normal stress and number of loading cycles increases. The results of the laboratory tests for normal behavior are used to determine the parameters to describe the interface stress-strain response. The model is shown to describe the hysteresis behavior of the interface as a function of amplitude of normal stress and number of loading cycles. The model is used to predict the results of cyclic normal tests and combined normal and shear tests, and was found to yield satisfactory results. The interface model is implemented in a 2D nonlinear soil-structure interaction finite element procedure. The finite element procedure is verified with respect to simple problems for which close form solution or laboratory results are available. The response of the force controlled cyclic test and combined normal and shear test is then predicted using the FE procedure and reasonable results are obtained. A pier foundation subjected to base displacement is then analysed for different combinations of soil and interface behavior. Computer results are qualitatively compared with displacement and contact stresses and the effect of including the interface behavior is identified with respect to debonding and rebonding of the interface. The results of this research have provided understanding of the cyclic behavior of sand-concrete interface subjected to normal and combined normal and shear loading. The interface behavior has been represented by simple mathematical model for which parameters can be easily determined from static and cyclic tests. The model is also defined for general loading to incorporate debonding and rebonding and it is easy to implement into a FE procedure.

The control of stresses and liquid pressure surges in pipes is an important problem in the design of hydraulic pipe networks. The method of characteristics has been used to solve the transient stresses and pressures in liquid-filled piping systems. The friction force is included in the equations of motion for the fluid and the pipe wall. The maximum pressure and maximum stress at any point along the length of the pipe are evaluated for the entire simulation time. A nonlinear search technique has been developed using the simplex method. The optimal valve closure is sought, that will minimize the maximum pressure and/or stresses. A continuous optimal valve closure policy is specified using spline functions. Numerical examples are presented showing the reduction of the dynamic pressure and the dynamic stress from linear valve closure to optimal valve closure for a simple pipeline and a complex pipeline. Also, a method for choosing the shortest time of closure which will keep the stresses below specified allowable stresses is presented.

A finite element formulation, based on assumed stress functions, is developed for the linear elastic analysis of the stresses in two-dimensional elasticity problems, including multiply-connected regions and flat plate bending. For planar analysis the Airy stress function is utilized. The physical significance of the Airy stress function and its normal derivatives are brought out. A new technique is introduced to account for traction type boundary conditions. A family of rectangular finite elements, which enables the direct insertion of stress type boundary conditions, and two higher-order rectangular elements which enable continuous stress variations along the interelement boundaries are constructed using blending function interpolants. In addition, a C° continuous triangular plate bending element is adapted for use as a plate stretching element. The Southwell stress function is employed for the analysis of flat plates in bending. A computer program is developed to substantiate the proposed methodology. The formulations are evaluated through the comparison of solutions obtained from the proposed method with classical solutions and solutions obtained from the assumed displacement finite element method. The elements are evaluated by solving the same example problem with different element types. Extensions of the proposed method to account for body forces, initial stresses, material nonlinearities, and shells are briefly discussed. It is demonstrated that the proposed method can directly be integrated with minimal modifications into existing general purpose finite element programs.

The stress-strain and volume (or pore pressure) change characteristics of a Southern Arizona copper mine tailings material were investigated in the laboratory by conducting static loading triaxial compression tests. The tailings material is silty sand with highly angular grain shapes, rough grain surface texture and approximately 37% by weight passing No. 200 sieve. Isotropically consolidated drained (CID) and isotropically consolidated undrained (CIU) tests were performed on laboratory compacted samples. The test samples were loaded to relatively large axial strains (20-35%) to study the residual shear strength and the shear stress induced pore pressure change or volume change at steady state. Test sample densities and effective confining stresses were systematically varied in these tests. The definition of critical void ratio and "lower" critical void ratio were reviewed and their values for different effective confining stresses were obtained from the CID tests. Stress-strain and volume (or pore pressure) change curves and strength parameters obtained by using conventional and lubricated loading end platens were compared and discussed. Steady state lines and undrained brittleness indices were obtained from the CIU tests with strain-controlled and load-controlled loading methods. The liquefaction potential of the tailings material was then evaluated. These results were compared with others reported in the literature. The significance of the results was discussed with respect to tailings material behavior.

The evolution of the large scale structures and the mean field were investigated in axisymmetric and plane mixing layers. Some aspects of the linear instability of an axisymmetric jet have been demonstrated. The axisymmetric geometry admits two additional length scales with relation to the two-dimensional shear layer: the radius of the jet column and the azimuthal wavelength. The importance of these two length scales in governing the instability of an axisymmetric jet was explored. The special case of a thin axisymmetric shear layer was analyzed and the results stressing the evolution of different azimuthal modes were compared with some phase-locked data which was produced by subjecting the jet to axisymmetric and helical excitation. The importance of the initial spectral distribution in a natural jet was demonstrated when it is used as an input to the amplification curve obtained from linear stability theory to predict a measured spectral distribution at a further downstream location. The inclusion of the nonlinear terms in the stability analysis reveals two main interactions: mean flow-wave interaction and wave-wave interaction. The modification of the mean flow of an axisymmetric jet was examined by exciting two azimuthal modes simultaneously. The interaction resulted in an azimuthal modulation of the mean velocity profile having a cosine shape. Effectively, the geometry of the jet was modified without changing the geometry of the nozzle. The coupling between an excited periodic disturbance and the mean flow was analyzed and the spatial evolution of both were compared with experimental results obtained in a plane mixing layer. The behavior of the concommittant Reynolds stresses is discussed in detail. The conditions under which one disturbance will transfer energy to another were derived and demonstrated in an axisymmetric jet. The interaction between a large amplitude plane wave with a weak subharmonic component was shown to enhance the amplification rate of the subharmonic. It was further shown that the nonlinear interaction between two azimuthal modes can produce a third azimuthal mode which was not initially present in the flow. The coupling between a fundamental wave and its subharmonic in a parallel plane mixing layer was demonstrated numerically.

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