Debonding failure in FRP-strengthened RC beams : prediction and suppression

Pao Yue-kong Library Electronic Theses Database

Debonding failure in FRP-strengthened RC beams : prediction and suppression

 

Author: Fu, Bing
Title: Debonding failure in FRP-strengthened RC beams : prediction and suppression
Degree: Ph.D.
Year: 2016
Subject: Concrete beams.
Fiber reinforced plastics.
Fibrous composites.
Reinforced concrete construction.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Civil and Environmental Engineering
Pages: xxxiv, 396 pages : color illustrations
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2890636
URI: http://theses.lib.polyu.edu.hk/handle/200/8497
Abstract: Flexural strengthening of reinforced concrete (RC) beams by bonding a fibre-reinforced polymer (FRP) plate/sheet onto their tension face (i.e. FRP-plated RC beams) is now widely accepted in practice. Such an FRP-plated RC beam often fails by debonding of various forms, including intermediate crack (IC) debonding and plate-end concrete cover separation. The former initiates at a major flexural/flexural-shear crack and propagates in the direction of decreasing moment; while the latter initiates at the critical end of the FRP soffit plate and propagates at the level of steel tension reinforcement in the direction of increasing moment. Despite extensive existing research on these debonding failure modes, two major knowledge deficiencies still remain: (1) the effect of load distribution on IC debonding; (2) the effect of FRP U-jackets in suppressing debonding failures. This thesis presents a systematic research project aimed at addressing these two issues. Following an introduction to the PhD research project and an extensive review of existing related research, an experimental study on IC debonding under different load distributions is presented. Five full-scale FRP-plated RC beams in two series were tested, with Series I addressing the effect of shear span and Series II addressing the effect of load uniformity. All five test beams failed by IC debonding, and the maximum moment in the beam at IC debonding (i.e. debonding moment) was found to increase as the load uniformity increased; the recorded increases in the debonding moment due to these two factors were up to about 20%. Following the experimental study, a finite element (FE) approach recently developed by the author's group was augmented with a novel displacement control technique and verified using the test results to produce reliable simulations of IC debonding under different load distributions. An FE parametric study was then conducted to extrapolate the test results. Existing IC debonding strength models applicable to different loading conditions were then assessed using both the test data and the numerical results, indicating the need for a more accurate IC debonding strength model. Attention was next shifted to the effect of FRP U-jackets on both IC debonding and concrete cover separation failures. Two series of tests on FRP-plated RC beams with vertical FRP U-jackets and inclined FRP U-jackets respectively were conducted to investigate their effect on IC debonding. The test results indicated that inclined FRP U-jackets performed much better than vertical ones and were capable of improving both the strength and ductility of the beam significantly. An experimental study on the use of FRP U-jackets of different forms to mitigate concrete cover separation then followed, in which ten full-scale FRP-plated RC beams were tested. Both the ultimate load and the ductility of the beam were found to be significantly enhanced by the U-jackets. Among the forms of U-jackets explored, those inclined at 45° were found to be the most effective. Finally, an approach for the design of FRP U-jackets for mitigating concrete cover separation was developed based on the 'concrete tooth' concept and verified using the test results obtained in the present research project.

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