Concrete bridges are in an advanced state of deterioration due to their age, the severe environmental conditions and the increasing service loads during the last centuries. Replacement of these imposing structures requires large amounts of money and inevitable logistics. Given these conditions, worthy of a pharaonic construction site, strengthening of these structures represents the perfect solution to extend their service life. The use of fibrereinforced polymer (FRP) composite materials is now one of the proven strengthening techniques. The advantages of this technique make it a better alternative compared to conventional strengthening with external steel plates. The behavior of reinforced concrete (RC) beams in shear depends on several complex and inter-related mechanisms and parameters including, amongst others, the size effect. The latter reduces the shear stress at failure as the size of the specimen’s increases. It occurs during the propagation of cracks in concrete and is governed by the fracture mechanics. The size effect phenomenon has been confirmed by several experimental studies on conventional RC beams. However, few studies have been devoted to shear-strengthened RC beams using externally-bonded FRP (EB-FRP). The main objective of this Ph.D. research study is to identify, theoretically and experimentally, the influence of size effect in RC beams strengthened in shear with EB-FRP. Another objective of this research is to evaluate the accuracy of the models of existing standards and codes. The experimental part of this study consists of carrying out two experimental programs on full-size T-beams of different depths strengthened in shear with EB-FRP including several study parameters. The exhaustive literature review allowed the development of database encompassing more than 470 test specimens on the size effect in shear of all types of RC beams. This database revealed, among other things, that the specimens devoted to FRP strengthening beams represent only 6%. The comparison of prediction model showed that current standards overestimate the shear strength attributed to EB-FRP in a significant number of specimens. Experimental results revealed the existence of an additional size effect attributed to EB-CFRP strengthening. This size effect also reduced the ductility of the specimens without transverse steel. In addition, the results revealed an interaction between the internal transverse steel and the externally bonded FRP, which reduces the resistance gain due to FRP. Major parameters influencing the size effect were identified in this research. These parameters require further investigations through extensive research programs.
| Date | 21 Jun 2021 |
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| Original language | French |
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| Awarding Institution | - École de technologie supérieure
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| Supervisor | Omar Chaallal (Supervisor) |
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Benzeguir, Z. E. A. (Author),
Chaallal (Supervisor),
21 Jun 2021Student thesis: Doctoral thesis › Doctorate in Engineering: Engineering