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The problem of the lateral instability of deep beams under the action of bending loads applied in tiieir planes of greatest flexural rigidity has been a subject of investigation by engineers since the introduction of the first rolled sections, over a century ago. The elementary theories for the determination of the bending stresses sufficient to cause failure of a beam by buckling have been evolved by a number of mathematicians, but there has been little experimental verification of these results by tests under prop@rly controlled conditions. Although the buckling of beams has been compared with, the failure of columns under end loads, the possibility of such beam failure in practice has been of far less importance than that of stanchion buckling--due,, primarily, to the fact that in most cases considerable restraints are applied to a beam under working conditions which invariably increase the loads necessary to cause instability. Also the materials in general use- have low specific strengths with limiting design stresses usually lower than the critical buckling stresses for beams of normal proportions. With the introduction as structural materials of high strength steels, and also of aluminium alloys having low elastic modulii, the problem becomes more crucial from the design aspect, and recently it has been found desirable to include design data, based on the fundamental theory, in new codes of Structural Engineering practice. The recent draft Code of Practice for Structural use of Steel in Buildings l contains clauses relating to the lateral stability of steel beams in which design formulae, deduced from the theoretical results for beams under idealised conditions, are suggested as alternatives to the existing empirical formulae in terms of the slenderness ratio L. This improved design data will give estimates of the permissible stresses in a beam which will generally be in error on the safe side and in many cases of beams used as floor joists or frame members it can be shown that failure due to lateral buckling cannot occur at flange stresses lower than the yield stress of the material, snd even then only as a secondary form of failure. The qualitative analysis of the influence of the various factors influencing the stability of beams under practical conditions may prove of great assistance to designers who at present sacrifice economy in their materials due to reduction of the allowable stresses as a precaution against buckling, -which may prove unnecessary when the actual conditions of loading and support are considered.

The response of a nonlinear dynamic structure can be sensitive to its initial conditions or parameters. In order to ensure its safety and robustness, an understanding of the global structural responses is necessary. This requires performing a parameter study. However, this is extremely difficult due to the complexity arising from nonlinearities and the associated computational costs. Hence, it is highly desirable to have new methods to tackle these difficulties.

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The web crippling strength of cold-formed plain channel steel section beams was investigated theoretically and experimentally in this research program. The web crippling strength in this thesis is termed the ultimate web crippling load and this was theoretically analysed using two different design specifications and a plastic mechanism approach. The two design specifications used in this research program were BS 5950 Part 5:1987 and European Recommendations For The Design of Light Gauge Steel Members, 1987. In the plastic mechanism approach, a plastic mechanism model of web crippling failure was developed and analysed using a method of yield line analysis. This approach has resulted in analytical expressions and these are specially used to analyse the ultimate web crippling load of the plain channel section beams subjected to combined actions of web crippling and bending. Besides the theoretical investigations, experimental investigations were also carried out for many plain channel section beam specimens of various dimensions. In the experimental investigations, test loads applied to the specimens were varied according to the loading conditions specified by AISI 1986 and they were transfered onto the specimens through various load bearing lengths. The experimental results were used to study the influence of various factors on the ultimate web crippling loads and to verify the theoretical results. The accuracy of theoretical results was statistically analysed and their deviations from the experimental results were limited within the acceptable scatter valus ± 20%. Some examples of the web crippling behaviour of the specimens characterized by their experimental load-deflection curves were also presented and, especially for the specimens under combined actions of web crippling and bending, their experimental load-deflection curves were compared to the theoretical collapse curves obtained from the plastic mechanism approach. Finally, the results of the experiments and the verification of each theory used in this research program are discussed and concluded in the last three chapters of this thesis. experiments a nd the verification of each theory used in this research program are discussed and concluded in the last three chapters of this thesis.

The use of GGBS as supplement for cements has been shown to improve the long-term strength and durability properties of concrete. In practice, while the chemical composition of GGBS from a single plant may be constant, due to the varying sources from which GGBS is obtained the chemical composition from plant to plant may vary. The wide variability in the use of GGBS as a SCM in different climates, coupled with differences in chemical composition, is bound to have impact on the performance of slag blends. This study investigated the combined influence of difference in slag composition and temperature on the performance of slag blends. Performance was evaluated in terms of strength and transport properties. Paste samples were characterised by calorimetry, TGA, XRD and SEM to follow hydration and microstructural development. Mortar samples were used to follow strength development and transport properties. All tests were carried out at temperatures of 20 and 38°C. Curing at 38°C accelerated the early hydration, but not the later hydration. This led to higher early strengths and lower later strengths, and was attributed to the coarsening of the pore structure caused by the high temperature curing. Except at the early ages at 20°C, both slag blends showed better strength performance than the reference cement. The slag blends also showed better transport properties than the reference cement, especially at 38°C, and this was attributed to their finer pore structure and higher chloride binding capacity. Of the two slags studied, the more reactive slag (slag 1) had better performance, especially at 38°C. Performance of the slag blends at 20°C was influenced mainly by the length of curing, and by the difference in chemical composition at 38°C.

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