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Title: Control of cracks by inclusion of fibres in reinforced concrete
Author: Ibrahim, O. T.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1982
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The main object of this investigation was to try to assess whether it is worthwhile to include steel fibres in structural reinforced concrete elements both from the mechanical and the economic points of view, with particular emphasis on the cracking behaviour of such elements. Therefore, a theory which predicts the crack spacing and width in fibre reinforced concrete elements was developed. This theory, though based on a number of assumptions, gave good agreement with experimental results of other workers. To examine the theory and to study the mechanical behaviour of fibres included in conventional reinforced concrete, a test programme was carried out on specimens subject to pure tension and on beams subject to bending. In the tension tests, continuous fibres were simulated by using regular array of small diameter reinforcing wire. The width of the cracks developed in these specimens was measured by an optical microscope. The use of the microscope, however, proved to be tedious and thus an automated method, based on the Moiré technique, was developed to provide a more convenient way of measuring the crack widths. This method, being accurate and efficient, was used in the beam tests. In these tests, the fibres replaced similar amounts of the reinforcing bars in a control beam. Thus, all the beams tested had the same total amount of reinforcements. During the initial analysis of the beam results, it became clear that assumption of a Gaussian distribution for the scatter in the crack widths at any particular load was incorrect and misleading, and a detailed statistical evaluation was carried out on these results. This showed that the Weibull distribution gave a very adequate representation of the scatter in the observations. The beam results showed that the use of adequate partitions of fibres and conventional reinforcing bars reduced the crack width and spacing, maintained the flexural stiffness of the beam and sustained the design ultimate load of the control beam, although with a reduced factor of safety. These results as well as the statistical analysis of the crack widths and spacing, have helped significantly in understanding the mechanical behaviour of the fibres in reinforced concrete and hence in refining the theory. Good agreement between the theoretical predictions and the beam results, as well as results of tension specimens tested by another worker, has been obtained. Using the theory developed in conjunction with economic considerations, it is shown that the use of the fibres can produce mechanical improvements in beam behaviour at a reasonable economic cost, particularly with the introduction of cheaper steel fibres.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available