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The last 10 years has seen a renewed interest in the behaviour of unreinforced masonry panels under earthquake loading. Research on full scale structures requires massive, expensive test equipment, is time consuming and costly in manpower. Full scale testing therefore, has been limited to specific, very narrow investigations. Modelling at a reduced scale offers immense savings with wider possible fields of study. The first stage of the author's work was aimed therefore at developing prototype materials for 1: 4 scale models, and establishing their fundamental mechanical properties. A complete description of the material properties should provide all the parameters for numerical and analytical predictions and for static and dynamic testing of prototype replicas at the small scale. The parameters investigated in the static testing phase included compressive, tensile and shear strength, Young's modulus and Poisson's ratio, shear modulus and brick-mortar interface bond among others. The second stage involved the development of a shaking table and the investigation of six low-aspect, confined, infill panels subjected to sinusoidal cyclic loading. The study investigated their dynamic behaviour and energy dissipation capacity with progressive damage. Parametric studies were conducted with respect to the brick, mortar and masonry strength. The damage was photographically documented and the cracking propagation is detailed from the initial stages up to collapse. Classic full scale cracking patterns and failure modes were observed which gave the author considerable confidence in the model results. Shear-ductile failures were recorded for panels confined by low axial compressive forces which seems in part to contradict some current opinion, but reference is also given to similar findings published recently in scientific journals. The final component of the work was concerned with a numerical assessment using a commercially available finite element program incorporating a non-linear concrete constitutive material model. This numerical model was fine-tuned by using the previously obtained experimental data to simulate cracking patterns of small masonry specimens under static load.

A review of Shakedown and Ratchetting concepts and their extensions is presented in an attempt to recount all the aspects of the problems considered in this research programme. The concept of Stress Concentration Factor was the first to be further investigated, by analysing two representative types of structures operating under severe stress concentration, namely; two-bar structures and cylindrical vessels with variable thickness subjected to cyclic mechanical loads. The material behaviour considered are: elastic-perfectly plastic and isotropic hardening. Such an analytical investigation allowed the assessment of the influence of the Stress Concentration Factor below and above the limit of reversed plasticity. The primary aim of this research was to develop simplified techniques capable of solving thermal loading problems in the presence of steady mechanical loads. A simplified technique was then developed to analyse a tube subjected to a complex thermal loading simulating the fluctuation of level of sodium in Liquid Metal Fast Breeder Reactors (LMFBR). The technique was also able to include a second important aspect of shakedown problems which is cases of multiple mechanical loads. The construction of bi-dimensional Bree type diagrams, from tri-dimensional ones obtained for such cases, allowed an easy assessment of the modes of deformation of the structure. The effects of the temperature on the yield stress were explored. A third aspect of thermal cyclic problems investigated was the experimental verification of the reliability of the extended Upper Bound Theorem proposed in Chapter 2. This was achieved by experimental tests on portal frames at 400°C. Contours representing states of constant of deformation were obtained from the experimental measurements. A fourth aspect of the problem was the development of theoretical technique to estimate the transient plastic deformation in excess of the shakedown limit which allowed the construction of theoretical contours directly comparable with the experimental ones. The fifth and major contribution of this thesis was the development of a general technique for the analysis of axi-symmetric shells based in a displacement formulation for the Finite Element Method. Limit analysis and shakedown problems were reduced to minimization problems by developing a technique to obtain consistent relationship between the displacement field and the plastic strain field. Such a technique, based upon a Galerkin type of approach, consist of minimizing the difference between the two representations of the strain within the element; in terms of nodal displacement and in terms of plastic multipliers. The problem was then solved by Linear Programming. Finally, the conclusions and proposal for future work are presented.

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No description available.

No description available.

Thesis (M. Phil.)--University of Hong Kong, 1998. / Includes bibliographical references (leaves 41-42).

Thesis (Ph. D.)--University of Maryland, College Park, 2006. / Includes bibliographical references (p. 151-157). Also available online.

Composite materials are increasingly being used in a wide range of structural applications. These applications range from bicycle frames and building facades to hulls of marine ships. Their popularity is due to the high specific strength and stiffness properties, corrosion resistance, and the ability to tailor their properties to a required application. With the increasing use of composites, there is a need to better understand the material and damage behaviour of these structures. In recent years, the increased frequency of wars and terror attacks have prompted investigations into composite failure processes resulting from air-blast. Most of the research has been focused on flat panels, whereas there is relatively little on curved structures. This dissertation reports on the effect of air-blast loading on concave, singly curved fibre reinforced sandwich and composite panels. Sandwich panels and equivalent mass glass fibre laminates were manufactured and tested. Three types of curvature namely a flat panel (with infinite curvature), a curvature of 1000 mm radius and a curvature of 500 mm radius were produced, to determine the influence of curvature on panel response. The laminates were made from 16 layers of 400 g/m² plain weave glass fibre infused with Prime 20 LV epoxy resin. The sandwich panels consisted of a 15 mm thick Airex C70:75 core sandwiched between the 12 layers of 400 g/m² plain weave glass fibre and infused with Prime 20 LV epoxy resin. This arrangement produced a balanced sandwich panel with 6 layers of glass fibre on the front and back respectively. For all panels, vacuum infusion was used to manufacture in a single shot process. Mechanical properties of samples were tested for consistency in manufacturing. It was found that mechanical properties of the samples tested were consistent with low standard deviations on tensile and flexural strength. The panels were tested in the blast chamber flat the University of Cape Town. Blast specimens were clamped onto a pendulum to facilitate impulse measurement. Discs of plastic explosive, with charge masses ranging from 10 g to 25 g, were detonated. After blast testing, a post-mortem analysis of the damaged panels was conducted. Post-mortem analysis revealed that the failure progression was the same irrespective of curvature for both the sandwich panels and the laminates. Sandwich panels exhibited the following failure progression: delamination, matrix failure, core crushing, core shear, core fragmentation, core penetration and fibre fracture. The laminates displayed the following progression: delamination, matrix failure and fibre fracture. Curved panels exhibited failure initiation at lower charge masses than the flat panels. As the curvature increased, the failure modes initiated at lower charge masses. For example, as the charge mass was increased to 12.5 g the front face sheets of the flat and the 1000 mm radius sandwich panels exhibited fibre fracture, but the 500 mm radius sandwich panel exhibited fibre fracture and rupture through the thickness of the front face sheet. The 500 mm radius laminate exhibited front face failure earlier (15 g) than the 1000 mm radius (22.5 g) and flat panel (20 g). Curved laminates exhibited a favoured delamination pattern along the curved edges of the panel for both 1000 mm and 500 mm radii laminates. As the curvature increased, more delamination was evident on the curved edges. The curved panels displayed more severe damage than flat panels at identical charge masses. Curved sandwich panels experienced through thickness rupture at 20 g charge mass whereas the curved laminates did not exhibit rupture at 25 g charge mass. The flat laminates were the most blast resistant, showing no through-thickness penetration at 25 g (the highest charge mass tested) and initiated failure modes at higher charge masses when compared to the other configurations.

Explosive threats have become more prevalent in both military and terrorist theatres of conflict, showing up largely in the form of Improvised Explosive Devices (IED) which are often buried in soil to conceal them and increase their effectiveness. The response of a structure subjected to a blast load is influenced by many factors, namely stand off distance, mass of explosive, degrees of confinement and medium surrounding the charge. This study focuses on characterizing the transient deformation of test plates which have been exposed to different explosive loading conditions including free air blasts (AIR), backed charge (VBP) and buried charge (SBP) configurations. In the three loading configurations, four charge masses are considered, utilizing 10g, 15g, 20g and 25g masses of PE4 plastic explosive which were moulded into cylindrical charges of a constant 38mm diameter. The transient deformation of the test plates was captured using high speed Digital Image Correlation (DIC), which utilized two high speed cameras to record the experiments. Extensive modifications to the blast pendulum to incorporate the cameras was necessary to adapt this technique in a different method to that used in previous literature. The mounting method proposed allowed the cameras to record the experiment while capturing the impulse imparted on a test plate using a blast pendulum. The experimental plates exhibited only Mode I failure, which is plastic deformation, enabling the effect of different loading configurations on the transient and final plate deformation profiles to be identified. Numerical simulations of the experiments were developed to further the understanding of the load arising from the three configurations and the deformation mechanisms involved. The experimental results are used to validate the numerical models, which allow for a better understanding of the evolution of the deformation and strains across the plate. The transient data for the numerical simulation and the experiments were found to match closely. This work clearly shows the effect that the different loading conditions have on the tests plates, specifically the impulse distributions and transient strain in the plates. It was observed in this study that the impulse imparted on a test plate increases with the addition of sand while keeping other test conditions constant. The impulse recorded was observed to increase by 490-540% and 19-100% when compared to AIR and VBP 50mm SOD tests respectively. The loading profile acting on the test plate as a result of the specific impulse changes significantly with the inclusion of sand. The midpoint deflection increases with a decrease in stand off distance, increase in charge mass, increase in level of confinement or the inclusion of an overburden of sand. The observed increase in midpoint deflection of between 90-160% and 30-40% when compared to AIR and VBP 50mm SOD tests respectively was reported. The transient plate profile does not match the final deformation profile.