No description available.

No description available.

This thesis essentially reports an investigation of the behaviour of buried (0.12 to 0.25m diameter) single-walled PVC-U and vitrified clay pipes during installation in a uniform sand surround and when subjected to applied surface loading. An additional simple study of tail void displacements due to tunnelling in sand is also presented. Controlled laboratory tests were conducted in a glass-faced, steel-sided box. The buried pipes were installed perpendicular to the glass face and were subjected to static and cyclic loading, simulating increasing overburden stress and the passing of traffic over a shallow buried pipe respectively. The simulated shallow tunnel tests were also conducted perpendicular to the glass and involved withdrawal of the outer of two concentrically placed tubes. Photographs were taken of the sand particles and the buried structure in the plane of the cross section together with strain gauge readings on the pipe or tunnel wall throughout installation and loading/shield withdrawal. The resulting sand displacements are presented in the form of horizontal and vertical contour plots. Pipe deflections and volumetric and shear strain contours of the sand were also determined for the buried pipe tests. The shape of the deformed pipe and the imposed stress at the pipe springline were inferred from the pipe wall strains. During the PVC-U pipe tests, the deformation of the pipe caused the applied stress to be transferred to the sidefill via arching in the surrounding soil. This was associated with a reduction of applied stress reaching the pipe. Increasing the initial soil stiffness reduced the magnitude of the pipe and soil displacements and the stress carried by the pipe. Use of a vitrified clay pipe however, caused the soil surround to settle relative to the pipe. Soil shear strain contour plots are used to highlight the mechanisms of the transfer of applied stress onto, or away from, the buried pipes, and are related to the shape of the deformed pipe in the PVC-U pipe tests. The test data also allowed standard buried pipe design methods and installation procedures to be critically appraised. The soil movements recorded during the tunnel tests were shown to be similar to those recorded during the buried PVC-U pipe tests, indicating a similar soil loading transfer mechanism.

In the design of piping systems the importance of the pipe bend is well established. Recent publications have been increasingly concerned with the effect of end constraints on the behaviour of smooth pipe bends. This has been aimed almost exclusively at in-plane bending, there being no serious attempts at the solution to out-of-plane bending. In PART (1) of this thesis a theoretical solution is presented for the out-of-plane bending of linear elastic curved pipes with rigid flanges. The analysis employs the theorem of minimum total potential energy with suitable kinematically admissable displacements in the form of fourier series. Integration and minimisation is performed numerically. Results are given for a wide range of practical bend geometries. A comparison with previous theoretical predictions highlights the inadequacy of these earlier solutions. The present results are shown to be in favourable agreement with results from tests conducted by the author and more recent results using a different solution procedure. Work in the creep of pipe bends necessitates a substantial amount of experimental work and expertise. Most publications dealing with the creep of pipe bends under bending loads fail to present much information on this aspect. In PART (2) of this thesis a general description is given of an experimental creep programme on pipe bends. The measurement of strain at elevated temperature was accomplished using the CERL-PLANER capacitance strain gauge. It is shown that the application of this gauge to pipe bends requires particular techniques if meaningful results are to be obtained. The results of development work arising from other problems encountered during the test programme are also presented. These include the measurement of displacement and distortion at elevated temperature and the provision of an efficient and novel heating system.

No description available.

No description available.

Thesis (M.Sc.(Engineering))--University of the Witwatersrand, Faculty of Engineering, 1999

Ribbed steel pipes made of Type 2 aluminized steel are commonly used for culvert pipes for highway drainage. Typically aluminized steel pipes have shown good durability and are expected to have long service life, e.g. 75 years; also, they are used in a wide variety of soil and water conditions. However, early corrosion of aluminized steel pipes has been recently observed in some inland locations. Initial observations showed severe corrosion in forms of pits, both along the ribs and at the nearby flat portions of the pipes. It is critical to determine the cause of early deterioration and establish methods of durability prediction. The possibility of unusual environmental conditions is being investigated elsewhere, but this research focuses on possible mechanical factors aggravating corrosion, since it is prevalent near pipe rib deformations. While forming the rib bends in the pipe, the outer bend surface is exposed to extreme tensile stresses which would cause small coating cracks (microfissures) exposing base metal. Those may lead to early corrosion as galvanic protection from the surrounding aluminum may not be sufficient under certain environments. Electrochemical impedance spectroscopy was used to measure corrosion rate of both formed and flat aluminized steel samples in simulated natural waters. Initial findings show that specimens formed by spherical indentation were susceptible to early corrosion development in moderately aggressive simulated natural water, but not in a more benign, precipitating simulated natural water solution.

This thesis explores the design of flexible pipes, buried in shallow trenches with dry sand backfill. The thesis reports the comprehensive analysis of twenty-two full-scale load tests conducted between 1989 and 1991 on pipe installations, mainly within a laboratory facility, at the University of South Australia. The pipes were highly flexible, spirally-wound, uPVC pipes, ranging in diameter from 300 to 450 mm. Guidelines were required by industry for safe cover heights for these pipes when subjected to construction traffic. The tests were designed by, and conducted under the supervision of, the author, prior to the author undertaking this thesis. As current design approaches for pipes could not anticipate the large loading settlements and hence, soil plasticity, experienced in these tests, finite element analyses were attempted. Extensive investigations of the materials in the installations were undertaken to permit finite element modelling of the buried pipe installations. In particular, a series of large strain triaxial tests were conducted on the sand backfill in the buried pipe installations, to provide an understanding of the sand behaviour in terms of critical state theory. Subsequently a constitutive model for the soil was developed. The soil model was validated before implementation in an element of finite element program, AFENA (Carter and Balaam, 1995). Single element modelling of the triaxial tests proved invaluable in obtaining material constants for the soil model. The new element was applied successfully to the analysis of a side-constrained, plate loading test on the sand. The simulation of the buried pipe tests was shown to require three-dimensional finite element analysis to approach the observed pipe-soil behaviour. Non-compliant side boundary conditions were ultimately adjudged chiefly responsible for the difficulty in matching the experimental data. The value of numerical analyses performed in tandem with physical testing was apparent, albeit in hindsight. The research has identified the prediction of vertical soil pressure above the pipe due to external loading as being the major difficulty for designers. Based on the finite element analyses of the field tests, a preliminary simple expression was developed for estimation of these pressures, which could be used with currently available design approaches to reasonably predict pipe deflections.

The possibility and feasibility of experimental detection of localized defects in tubes using laser-induced ultrasonic wave approach through Thermo Acousto Photonic Non Destructive Evaluation (TAP-NDE) and Signal processing through wavelet transform is examined in this research. Guided waves in cylindrical surfaces provide solutions for detection of different defects in the material. Several experiments were conducted to this respect. Wave propagation in both axial and circumferential directions was studied. The dispersive wave propagation of ultrasonic waves in hollow cylinders has been investigated experimentally, primarily for use in non-contact and nondestructive inspections of pipes and tubes. The laser ultrasonic waves propagated in cylindrical waveguides are particularly attractive because of their unique characteristics in the applications of nondestructive evaluation (NDE). Contrary to studies making use of only axially symmetric guided waves in hollow cylinders, here are analyzed also nonaxisymmetric waves. The analysis of data is made by using the Gabor wavelet transform. The capability of modeling the guided wave dispersion in hollow cylinders is used in developing guided wave experimental techniques for flaw detection. Good agreement was obtained when comparing the dispersion spectra between theory and experimentation. Measurement of group velocities of guided waves, which are obtained directly from the wavelet transform coefficients, can be used to determine allocation and sizing of flaws.