Flexural strengthening

When considering an intermediate debonding (mode 2), the resistance at ultimate limit state shonld be determined as follows. In order to prevent debonding in mode 2, the variation of strength between two consecutive cracks in FRP reinforcements shonld be prevented from exceeding a specific limit value. The latter generally depends on the features of the adhesive bond, on the distance between cracks, and on the level of strength Of in the reinforcement. 

Alternatively, a simplified procedure can be adopted consisting of verification that the strength on the fiber-reinforced composite at the ultimate limit state does not exceed a maximnm value, dd,2. given by the following relation  

with specific data missing, the factor can be assumed to be equal to 3.0. The corresponding value of the design strain of fiber-reinforced composite, e, is  

To verify the interface strengths at the serviceability nltimate limit state, it should be noted that tensile concentrations (tangential and normal) exerted on a reinforced beam with composite materials at the interface between the conaete and the reinforcement are localized close to the transversal cracks existing in the concrete, particularly at the extreme ends of reinforcement. These concentrations can cause the interface to crack, thus leading to a debonding between the two materials. 

This should not occnr during service, particularly in the presence of loading cycles and of freeze-thaw cycles. A suitable verification can be carried out by calculating the interface strength using linear elastic models. 

---

Key words FRP bars, externally strengthening, FRP profiles, confinement, flexural strengthening, shear strengthening. 

Fibre reinforced polymer (FRP) composite materials for flexural strengthening... 

Flexural strengthening with strips of a soiid siap fioor in Warsaw due to ioad eniargement (photo Prof. Kotynia). 

Debonding failure modes of externally bonded flexural strengthening (EBFR). 

Shear and flexural strengthening due to new holes in a beam in a building in Switzerland (photo Empa). 

Shear and flexural strengthening with strips and fabrics in a cement factory in Poland (photo S P). 

Similar to the design of flexural strengthening, the following states for the shear design of reinforced concrete (RC) members can be distinguished as the stmctural loads increase ... 

Kim, Y. J., R. G. Wight and M. F. Green (2008). Flexural strengthening of RC beams with prestressed CFRP sheets Development of nonmetallic anchor systems. Journal of Composites for Construction 12(1) pp. 35-43. 

Norris T, Saadatmanesh H, Ehsani MR, Shear and flexural strengthening of R/C beams with carbon fibre sheets, J Structural Eng, ASCE 123(7), 903-911, 1997. 

The research on the potential use of FRP composites in structural strengthening was first started for the flexural strengthening of RC beams. Prior to this research on FRP plate bonding, a considerable amount of research had already accumulated on steel plate bonding for flexural strengthening of RC beams and much of what was learnt in this research is relevant to FRP plate bonding. 

As a flexural member, the behaviour of one-w ay slabs is very similar to flexural behaviour of beams and, as far as the FRP reinforcement is concerned, the behaviour of two-v ay slabs can be taken as uncoupled bending in two orthogonal directions. It is probably for this reason that there is much less work reported in the literature on the flexural strengthening of RC slabs using FRP composites. 

Comparison of Standards About Flexural Strengthening Table 4.2 ACI code... 

The flexural strengthening with composite materials can be performed by applying one or more laminates, that is, different layers of sheet to the tensioned side of the member to be strengthened (Fig. 5.4). 

Fig. 10.3 Shear and flexural strengthening of r.c beams with CFRP...

Flexural strengthening with CFRP strips of reinforced concrete (a) beam and (b) slab (prestressed strips courtesy of S P Clever Reinforcement). 

FRP external strengthening of concrete structures (a) flexural strengthening of a concrete beam using carbon FRP laminates ... 

Barros, J.A.O., and Fortes, A.S. (2005). Flexural strengthening of concrete beams with CFRP laminates bonded into slits . Cement Concrete Composites Journal, 27(4) 471 80. 

Bournas, D.A., and Triantafillou, T.C. (2009). Flexural strengthening of reinforced concrete columns with near-surface-mounted FRP or stainless steel . ACI Structural Journal, 106(4) 495-505. 

Hacha, R., and Rizkalla, S.H. (2004). Near-surface-mounted fiber reinforced polymer reinforcements for flexural strengthening of concrete structures . ACI Structural Journal, 101(5) 717-726. 

The flexural strengthening of RC bridge beams by the technique of Near Surface Mounted (NSM)... 

Bogas, J. A. and Gomes, A. (2008), Analysis of the CFRP flexural strengthening reinforcement approaches proposed in fib bulletin 14 , Construction and Building Materials, Issue Vol. 22, 10, pp. 2130-2140. 

De Lorenzis, L., Micelli, F. and La Tegola, A. (2002), Passive and active near surface mounted FRP rods for flexural strengthening of RC beams . Proceedings of the International Conference on Fibre Composites in Interface - ICCI-02, 10-12 June 2002, San Francisco, CA (CD ROM). 

Hassan, T. and Rizkalla, S. (2002), Flexural strengthening of post-tensioned bridge slabs with FRP systems , PCI Journal, Vol. 47, Issue 1, PP- 76-93. 

---