Application of the theory of bending to the structural members of ships

Yuille, Ian M (1957) Application of the theory of bending to the structural members of ships. PhD thesis, University of Glasgow.

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On my return to employment in a shipyard design office after graduating in 1947, I was required to solve many problems of a non-routine nature. These were associated with almost every branch of naval architecture, but structural strength problems predominated and most of the latter were concerned with the local strength of the structural members of ships rather than strength of the hull as a whole. When the opportunity arose for me to carry out research at the University it was not unnatural that I should chose to examine this problem. The main objective was to decide what precautions must be taken when using the theory of elastic bending to analyse the strength of the structural members of ships and to formulate a suitable theory which could be applied in the design offices of shipyards. With the latter end in view it was necessary that the final theory should be as simple as possible and, bearing in mind that in general neither the loads applied to most ship structures nor the strength characteristics of the materials used were accurately known, it was permissible to omit refinements of the theory which would affect the results by less than a few percent. To achieve this object the stresses and deflections measured in the experiments at Glengarnock were compared with those predicted by the theory of bending, and the theory was modified until it could be made to agree with the measurements with reasonable accuracy. This analysis was supplemented by some experimental work on board ship which showed that the theories developed could be applied also in practice. Although the research did not necessarily proceed in a straightforward manner the results are presented in this thesis in a logical sequence. There are five main chapters with a review of the work in a sixth chapter, and an Appendix. Two problems which were peculiar to shipbuilding appeared to be important. The first of these was the difficulty of deciding what degree of constraint there was at the ends of the structural members of ships. To enable this to be taken into account I modified one of the most useful tools of structural analysis - the method of moment distribution. An early version of the theory was sent to the Institution of Naval Architects in an interim report on the research and was published in 1952 (ref. Al), but later revisions were so extensive that a full account of the final theory is given in Chapter I of the thesis. The theory allows for the constraint at the ends of loaded beams which may be straight or curved in the plane of the applied loads and may have constant or variable cross sections. The second problem was that of shear lag in stiffened plating. This occurs in ships and aircraft and had received a good deal of theoretical attention. Many of the theories indicated conflicting results and hardly any experimental work had been published; the G-lengamock results were inconclusive. I therefore investigated the matter by theory and experiment, and the results were published in 1955 by the Institution of Naval Architects. A copy of this paper, together with the discussion, is bound as an Appendix at the end of the thesis and a summary (and one small extension which has a bearing on later work) is given in Chapter II. It is shown that shear lag is usually unimportant in shipbuilding, but a new method of calculating shear lag effects is described for use when required. With this foundation it was found to be possible to commence an analysis of the Glengarnock results and this is discussed in Chapter III. Altogether the results of about 300 experiments were examined. It was found to be possible to correlate a large number of these by means of the theory described in Chapter I, Further modifications or additions to the theory of bending were required in order to account for discrepancies noted in certain classes of specimen, and these are discussed as they arise. An attempt to predict the experimental results entirely from theoretical considerations met with a fair amount of success, A paper on the analysis is nearly ready for submission to the Institution of Naval Architects. In Chapter IV there is a description of some experiments which I carried out on board ship. Measured deflections are compared with those predicted theoretically and, although agreement is not perfect, it is shown that it is possible to estimate fairly accurately the constraint at the ends of a bulkhead stiffener with welded brackets, at any rate in this particular case, by the theory outlined in Chapter I, The theories described are all based on elastic analysis of beams but in Chapter V there is a brief discussion of the possibilities of using the theory of plastic bending in shipbuilding. This is followed in Chapter VI by a review of the research and some conclusions and suggestions for further work.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: James Small
Keywords: Naval engineering
Date of Award: 1957
Depositing User: Enlighten Team
Unique ID: glathesis:1957-73559
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jun 2019 08:56
Last Modified: 14 Jun 2019 08:56

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