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A computer program is developed to determine the buckling stress and deflections of symmetric corrugated core sandwich panels. In the program freedom for lateral deflections at core to face-plate junction is allowed for. Provision is also made to study the effect of variation of core bend radius. A range of test specimens using four basic core configurations is designed to assess the effect of core bend radius on the buckling stress of the panel. The computer program indicates that above a certain value of core bend radius there is a marked drop in the value of critical buckling stress and a change in buckling Mode. The values of deflections at core to face-plate junctions at low buckling wave-lengths are not reliable* Due to the limited range of the experimental work, it is not possible to draw any conclusions on the effect of core bend radius on the buckling stress. The method used for determining the experimental buckling load is somewhat subjective in application, and its accuracy is difficult to assess. In general, the experimental values of buckling stresses are 15% higher than those predicted by the computer program. These discrepancies are not large when dimensional and material property variations are considered and indicate that the computer results are giving the correct trend and are conservative. Recommendations are made for : (i) Investigation of the buckling deflections at low values of buckling wave-lengths for specimens with high face-plateto-core thickness ratio. (ii) A test programme covering a wider range of specimens than that covered by the test programme in this study. and (iii) Trying out the other two methods of determining the buckling load.

This thesis is a study of the stress-distribution and buckling behaviour of a perforated square plate in shear. The large deflection buckling of an unperforated shear web is also studied. The finite difference technique is used for the solution and the electronic computers "Mercury" and "Atlas" were used for calculation. The stress distribution in a perforated plate was studied under two limiting boundary conditions, namely, (0 the square boundary of the plate is assumed to be rigid and remaining straight during shear deformation; (ii) the applied shear stress along the square boundary is uniform. Finite difference solutions for the hole size/plate width ratios k = 0.5 and 1.0 were obtained. Experimental results were obtained for the rigid boundary case and for various hole sizes. Finite difference solutions for the large deflection buckling of an unperforated shear web under four different boundary conditions are obtained. However, experimental investigation included only the case of the rigid and clamped edge. Finally, the buckling of a perforated shear web with k = 0.5 is studied. A number of the finite difference solutions were obtained, but these arc not satisfactory. Experimental results were again obtained for the case of the rigid clamped boundary with various k values.

A simplified theory is developed for calculating the creep buckling of components in the form of prismatic bars, and extended to cover the case of two-member components such as reactor fuel elements. The rate modulus (evolved at the mean stress) approach is used and all phases of creep and elastic strains are considered. For the two-member components it is shown that a solution in closed form can only be obtained when the mean stresses in the components remain constant. In general this will not be the case and a graphical method of solution involving isochronous stress-strain curves is suggested. Throughout the analysis a modified form of the Andrade tensile creep equation proposed by Graham and Walles is assumed. Results of creep buckling experiments on E1C-M commercially pure aluminium rods and on magnox A.12 rods are presented, together with data for the creep buckling of composite specimens of the two materials, and compared with the theory.

Columns in general can be regarded as built up of components. These components may be of different structural form, such as the column legs and the latticing of a Latticed Column, or may be of the same form, such as the flange and web plates of a Thin Walled Column. In any one case failure may occur either by integral column action - "Overall Instability" or by failure of one of the components - "Component Instability". The contents of the thesis are divided into two main parts. Part I presents a review of published Analytical and Experimental Investigations of Latticed Columns, followed by a short critical discussion. This reveals, on the experimental side, the lack of complete column distortion data and on the theoretical side, the absence of stability analysis of the column leg components as distinct from the panel elements. The review is followed by the presentation of the experimental work carried out on a model latticed column, from which the complete distortion of the column legs were obtained by measurement of the lateral deflections at 18 points along their length. Using the experimental work as a guide an analysis is developed, which gives the buckling load of Latticed Columns based on the stability of the column legs. Account is taken of the action of lateral loads' on the column legs, the magnitude of these loads being dependent on the elasticity of the latticing. In its application, the critical stress given by this treatment is taken as the "ideal column" buckling stress of the Perry-Robertson formula, which is then utilised to complete actual failure stresses. Values calculated in this manner are compared with the published experimental results of other Investigators. Part II gives a brief survey of the relevant published theories of flexural and torsional integral column stability, and flexural plate stability under compressive actions. The thesis then presents the experimental work carried out on thin walled columns consisting of some 70 tests to destruction of 3 ft. long channel section specimens. The tests were designed to cover the complete range of integral column and plate component failure. Special study was made of the conditions obtaining under simultaneous overall column and plate component collapse. The characteristics of flange plate failure were further investigated on two 12 ft. long channel section columns tested to destruction. Complete edge deflection data for the flanges together with a stress survey of the flange surface are presented. The experimental buckling stress results of the plate failure range, are analysed on the basis of the classic plate buckling theory, leading to the evaluation of the degree of edge fixity of the flange plates. This is followed by a comparison of the experimental results with calculated distributions given by the Perry-Robertson formula - the plate critical stress being taken as the "ideal column" buckling stress and by the present day stress basis of American design. The findings of the investigations presented in the thesis fall into two categories, namely (i) Specific characteristics - appertaining to details of theoretical and experimental behaviour. These are given in the Summaries at the end of each section. (ii) General features appertaining to a substantiation of the Perry Robertson formula, while developed originally for the "Overall" type of failure it is shown to be applicable to the "Component" failure range also provided the values of the imperfection factor and the "ideal column" buckling stress correspond to the characteristics of the weakest column component.

The problem discussed in the following thesis is that of the effect of stiffener dimension on the buckling of webplate subjected to bending. In Chapter one the problem of buckling is introduced generally and various examples of the use of horizontally stiffened webplates are mentioned. The theoretical background to the problem of the stability of plates both stiffened and unstiffened is contained in Chapter (2) together with reference to the advantages and disadvantages of various stiffener positions. Chapter (3) contains an account of a number of experimental investigations carried out on plates and girders with problems of stability relevant to the present problem. The various methods of examining these problems are also illustrated in Chapter (3). The phenomena of plate buckling is discussed in Chapter (4) together with the various methods of measuring the buckling load. The physical changes caused by buckling which are used for the purpose of measuring the buckling load are discussed and the best possible arrangement of apparatus for performing the measurements are also suggested in this chapter. In Chapter ( 5) the procedure adopted for testing is discussed and the use of sane of the methods of measurement discussed in Chapter (4) are illustrated. Here also the aims and objects of the experiments are stated. The results obtained from the experiments are discussed in Chapter (6). Discussion is first centred upon the results obtained from plates with double-sided horizontal stiffeners, starting with stiffeners at the fifth depth position and going on to stiffeners at mid-depth and those at the quarter depth. Later in this chapter the results from plates stiffened on one side only are surveyed in a general manner and this is followed by a comparison in behaviour between plates stiffened horizontally on both sides and those stiffened horizontally on one side only. The section on non-destructive tests is concluded with an examination of the effect of varying the rigidity of the double­ sided vertical stiffeners. As a preface to the section of Chapter (6) devoted to tests to failure, a study was made of the deflection contours produced in two of the girders when under load. The purpose of these contour tests was to enable the positions of the buckle-crests to be pin pointed in order to fix strain gauges in the appropriate positions. As a result of the contour plots, positions were fixed for the strain gauges for use during the failure tests and the layouts are shown at the beginning of the section of Chapter (6) on destructive tests. The results obtained from the strain gauges illustrated the development of the stresses and strains in the girder and allowed a study of the post­ buckled behaviour of the girders to be made. The results obtained gave information on the behaviour of girders initially plane and girders which were subject to sane initial imperfections. These results threw some interesting light on the comparative behaviour of the girders in these two states.

The thesis presents a theoretical and experimental investigation of the buckling of flat rectangular plates when subjected to symmetrical and asymmetrical temperature distributions over their lateral surfaces. These temperature distributions induce thermal stresses. Under certain conditions the compressive component of the induced thermal stresses causes the plate to buckle out of its own plane. The evaluation of the critical temperature, which initiates buckling, is carried out in two successive steps. 1. A solution of the biharmonic equation that governs the distribution of thermal stresses under stable conditions is obtained. 2. This stable state distribution of thermal stresses is utilised to obtain an approximate solution of the equation governing the stability of flat plates with internal varying stresses. This gives the value of the critical temperature at the onset of buckling. The subject matter of the thesis is divided into four parts PART I is a review of the published literature covering rigorous and approximate methods which have been used to determine the stable state distribution of thermal stresses and the evaluation of the critical buckling temperature. It also includes considerations of plate deflections in the post-buckling range with particular reference to the growth of the plate centre deflection with increasing values of plate temperature differential. PART II deals exclusively with the theoretical analysis and evaluation of the critical buckling temperature. It includes, as its first consideration, the determination of the steady state distribution of thermal stresses in the plate. An approximate solution of the biharmonic equation, governing the distribution of stresses is presented using the Kantorovitch. Method. This is followed by an original application of the Rayleigh-Ritz Method, to obtain an approximate solution of the biharmonic equation giving the thermal stresses in a polynomial form. This is followed by an investigation of the effects of plate aspect ratio and the degree of asymmetry of the temperature distributions on the value of critical temperature. The cases considered have, to the author's knowledge, not been investigated hitherto. The numerical work associated with the theoretical analysis was carried out on a 'Deuce' Computer using Alpha Code and General Interpretive Programmes. PART III presents the experimental work carried out in substantiation of the theoretical methods used in Part II. This covers the determination of the critical buckling temperatures and deformations of aluminium alloy plates, of aspect ratios ranging from one to three, subjected to symmetrical and asymmetrical temperature distributions. PART IV discusses, critically examines and summarises the comparison and correspondence obtained between the theoretically predicted and experimentally determined values of critical temperatures and deformations. It is shown that good agreement exists. The thesis concludes with six appendices which present detailed analyses and calculations followed by a bibliography.