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Title: Combined shear and bending of reinforced concrete members
Author: Regan, Paul Erskine
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1967
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The object of the research reported in this thesis, was to formulate a theory of shear in reinforced concrete, which was both logically acceptable and reasonably accurate, while at the same time being simple enough to be of practical use. The main outline of the known behaviour of members subject to shear is described, and existing shear theories are reviewed in the light of it. The inadequacies of the various theories are discussed. To a large extent, these stem from the fact that the majority of the present-day methods was derived empirically on the basis of very limited test data and is found to be inapplicable in more general cases. A few analytical approaches are so complicated as to be virtually unusable. The approach to shear, developed in the major part of this thesis, consists of two separate theories. The first is concerned with shear cracking, and is based on an analysis of the stresses in beams immediately prior to the occurence of shear cracks. The determination of stress distributions is dependent on widely accepted stress-strain relations, and the criteria of local failure, or cracking, used is shown to be as accurate as any and generally safe. The results obtained by the analysis are approximated to by simple equations. The second part of the theory relates to the behaviour of beams with shear cracks. This requires a new analysis of stresses, as the internal structure of a beam is radically changed by such cracks. The internal structure is complex and indeterminate, both in the statical sense and in the sense that its geometry is unknown due to the unknown disposition of cracks. Under some circumstances this structure is incapable of supporting the load that causes the shear cracks to form. In these cases the previous shear cracking equations also serve to determine ultimate loads. In other cases, in which an increased load can be sustained following shear cracking, a solution for the ultimate strength is obtained by using a set of three simultaneous equations. One relates the area of uncracked concrete, capable of supporting load, to the properties of the beam and the lengths of shear cracks. It is based on a compatibility condition not very different from those used in other recent shear theories. The second equation is an extension of the original shear cracking theory, and enables the lengths of shear cracks to be related to the properties of the beam. This is a type of equation that has not been used previously. The third and final equation is the basic failure criterion and very simply relates the ultimate load to the strength of the uncracked zone of concrete, in which failure occurs. It is shown that there exists a number of secondary modes of failure associated with shear cracking; that the resistance of a beam to such failures cannot be determined by the theory outlined above, and is not in fact amenable to precise analysis. Simple methods of dealing with such secondary modes are given, in terms of safe limiting strengths and/ or detailing requirements. The details of 25 tests are also presented. The object of the tests was to investigate the effects on shear strength of a number of quite normal types of detailing for which little or no previous data was available. In some eases the results are inconclusive, but in general the behaviour of the beams was in agreement with the predictions of the proposed theory. In the form described, the theory constitutes a relatively comprehensive and theoretically reasonable method of analysis. Its accuracy and those of the more accepted earlier theories are checked against a very large number of test results, and it is shown that the proposed method is more accurate and more economical than the others. Suggestions are made as to ways in which the range of applicability of the theory could be extended, and the work required to do this is discussed. Although the theory is simpler to use than previous analytical methods, and could be used by a competent designer, it is more complex than some empirical approaches - in particular it is more complex than the recently published American design recommendations. A final chapter is therefore devoted to the development of very simple design proposals suitable for inclusion in a Code of Practice.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available