This thesis describes an investigation into the buckling, post-buckling behaviour and collapse of simply supported square and rectangular plates with centrally located circular holes. The review of the current literature is preceded by a brief description of the approximate methods of plate buckling and post-buckling analysis. The basic equations of compatibility, equilibrium and strain energy are described. Theoretical analyses of the pre-buckling, buckling and post-buckling behaviour are presented. The pre-buckling analysis is by the finite element method and the buckling and post-buckling analyses use the minimisation of total potential energy. The buckling analysis uses the prebuckling stress distribution with an approximate out-of-plane deflection function with arbitrary coefficients. The post-buckling analysis uses finite element and analytical stress distributions to ensure internal equilibrium and assumes that the out-of-plane deflected shape is the buckling mode. A simple collapse analysis was also presented. An experimental programme is described which was carried out to determine buckling loads, post-buckling deflections and collapse loads. The experimental investigation of the distribution of strains along the plate centre lines is also described. Comparison of the theoretical results is made with the results of the experimental investigation and, in addition, with the theoretical and experimental results of other investigators. These results are all fully discussed and the conclusions drawn from the discussion are presented. The thesis is ended by three appendices, the first of which describes and discusses the derivation of the finite element plane stress stiffness matrix, and the second describes the method of determining the smallest eigenvalue. The third appendix describes the material properties of the plate specimens, and their derivation.

All the previous works on Framed-tube structures required the services of a digital computer of reasonable size to obtain a solution. There appears to be a distinct need to develop a simple method which will enable hand-calculations to be carried out rapidly in the early stage of design to give a reasonable, assessment of the structural behaviour and to make preliminary estimates of the main structural element sizes. In the simple approximate analysis presented in this thesis, the rigidly-jointed perimeter frame panels are replaced by equivalent orthotropic plates, whose properties are chosen to represent both the axial and shearing deformation characteristics of the frames. The use of an artificially low shear modulus G enables the racking deformations of the frame to be simulated. The stress distributions in the panels are assumed to be represented with sufficient accuracy by polynomial series in the horizontal coordinates, the coefficients of the series being functions of the height coordinate only. After satisfying the equations of equilibrium, the unknown functions are determined from the principle of least work by means of the calculus of variations. Two methods of analysis are suggested. In the first very simple method the stress distributions represented by the basic beam theory are modified to include the effects of shear lag. Closed form solutions are presented for three standard load cases, a uniformly and a triangularly distributed load, and a point load at the top. Design curves are developed to enable solutions to be obtained rapidly. A limited study is carried out to examine the effects of variable corner column stiffness and the ratio of column width to spandrel beam depth on the optimisation of the Framed-tube structure. A more general analysis of the Framed-tube structure yields simultaneous differential equations for the two unknown functions which are solved for the three standard load cases. The effects of an elastic base on the boundary conditions of the Framed-tube structure are considered. Framed-tube structures with different stiffness regions are also examined. An analogous simplified method is presented for the analysis of Framed-tube structure subjected to torsion. Closed form solutions, and associated design curves, are presented for the three standard load cases. The behaviour of Bundled-tube structures is more complex and a number of simplifying assumptions are made to reduce the number of unknown functions to a manageable size. Both simple and more general methods are presented for the analyses of such structures with two and nine modular tubes. A method is presented to consider the likely effects of the flexibility of the spandrel beams on the stress distribution in a Framed-tube structure subjected to vertical forces. A number of numerical examples are given which illustrate the various aspects of the theories developed and enable the best disposition of the materials to be made. The results from a series of tests carried out on Perspex models are compared with the theoretical values in order to assess the validity of the approximations.

The measurement of moisture content within construction materials is a useful capability for researchers investigating the building physics associated with material durability, and also for building professionals seeking to diagnose the cause of building defects. Various tools have been employed by both groups. However, research tools are often impractical for use on site, and highly portable techniques used by building professionals often have limited accuracy and applicability. This study investigates the use of Time Domain Reflectometry (TDR) for in-situ measurement of moisture content within building materials; this technique has the potential to be useful for both user groups. Time Domain Reflectometry has established applications in the soil sciences. The basis for the technique is measurement of the relative permittivity of a dielectric medium adjacent to waveguides; this is dominated by the presence of moisture. This study has developed probes suitable for installation by carefully drilling holes within construction materials. Experimental work has been undertaken to evaluate the TDR response to changing moisture content in a range of materials. The study has demonstrated that the technique will assess long term trends in relative moisture content of a porous material with minimal preparation. Measurement of absolute moisture content is found to be considerably more complicated, being particularly influenced by the contact quality between the probe and the measured material. Experimental work has explored the contact quality associated with the TDR measurement; this has resulted in a mathematical description proposed to account for the contact quality with the TDR measurements. Statistical reanalysis of experimental results using the contact quality model has successfully demonstrated an improved evaluation of absolute moisture content consistent with other direct laboratory measurement techniques. Finally, the study identifies considerations for others interested in using TDR for measuring moisture content within a solid material. The study also suggests potential areas of research which would enhance the capability of TDR to measure moisture content within construction materials.

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