Experiments on concrete beams strengthened by bonding fibre reinforced plastic sheets

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Experiments on concrete beams strengthened by bonding fibre reinforced plastic sheets


Author: Hau, Kin-man
Title: Experiments on concrete beams strengthened by bonding fibre reinforced plastic sheets
Degree: M.Sc.
Year: 1999
Subject: Concrete beams -- Testing
Reinforced concrete, Fiber
Fiber reinforced plastics
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Civil and Structural Engineering
Pages: viii, 82 leaves : ill. (some col.) ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1479991
URI: http://theses.lib.polyu.edu.hk/handle/200/101
Abstract: The objective of the dissertation is to investigate the structural behaviour of simply supported concrete beams strengthened by bonding fibre reinforced plastic (FRP) sheets. The beams were loaded by two concentrated loads at third span points. The length of the FRP sheet was the main parameter of the study In addition, the texture of the beam soffit was also varied to see if there is any implication on the performance. The FRP sheet was made from a fabric sheet and epoxy in a wet lay-up process in the laboratory and was then placed on the beam soffit without an additional adhesive layer. This is different from the usual bonding practice of using steel plate or FRP plate. The effect of this construction process on the debonding failure strength is a main concern of this study. Eight tests were carried out for the dissertation. The experimental results showed that the strength of the concrete beams was increased in general with maximum gain up to 70% of the original strength when a long FRP sheet was used. For beams with shorter FRP sheets, failure was by concrete peeling off with little improvement to the strength. The maximum interface stresses at the adhesive layer for each beam were calculated by using the formulas proposed by Roberts (1989). It have been identified that both the maximum shear stress and normal stress are in the range of 5.7-7.9N/mm2 and 2.9-3.6N/mm2 respectively for failure due to concrete peeling off. The values are higher than those recorded by Robert (1989) for steel plate which should be in the range of 3-5N/mm2 and 1-2N/mm2 respectively. Due to the low elastic modulus of the FRP sheet, the improvement on deflection of the strengthened beams is only marginal. Based on the experimental results, initial cracks developed at approximately 15kN for all the tests. This demonstrated that the FRP sheet adopted for the tests had no significant contribution on the improvement of initial deflection.

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