Flexural strengthening of concrete beams with CFRP laminates bonded into slits

Abstract

Near surface mounted (NSM) strengthening technique using carbon fibre reinforced polymer (CFRP) laminate strips was applied for doubling the load carrying capacity of concrete beams failing in bending. This objective was attained and the deformational capacity of the strengthened beams was similar to the corresponding reference beams. The NSM technique has provided a significant increment of the load at serviceability limit state, as well as, the stiffness after concrete cracking. The maximum strain in the CFRP laminates has attained values between 62% and 91% of its ultimate strain. A numerical strategy was developed to simulate the deformational behaviour of RC beams strengthened by NSM technique. Not only the load carrying capacity of the tested beams was well predicted, but also the corresponding deflection.

Near surface mounted FRP reinforcement for strengthening of concrete structures

“…The bending moment vs. deflection indicates considerable increases both for maximum moment and for maximum deflection in case of NSM reinforcement (Figure 7). [14] In Portugal carbon FRP strips were applied on RC beams as result they doubled the ultimate load of the corresponding reference beam (Figure 8). They increased the load with 32% to 47% at the onset of steel reinforcement yielding.…”

An experimental study on shear reinforcement in RC beams using CFRP-bars

“…When NSM is used, the appearance of a structural element is practically unaffected by the strengthening intervention. Since both faces of the laminate are bonded to concrete when using CFRP laminates, high strengthening efficacy has been attributed to the NSM technique for both flexural (Barros and Fortes, 2005;ElHacha and Rizkalla, 2004;Wang et al, 2009;Ali et al, 2008;Badawi and Soudki, 2009) and shear strengthening (Islam, 2009;Novidis et al, 2007;Yang and Wu, 2007) of concrete structures. The idea of this research comes from the near-surface mounted (NSM) method.…”

Load-bearing capacity of flexural reinforced concrete members strengthened with fiber-reinforced polymer in fracture stage

“…The experimental results are collected from different scientific publications. 19,20,[22][23][24][25][26][27] A focus is made on the assessment of crack depth of critical normal section and evaluation of FRP strainstress relationship. The stiffness of strengthened flexural RC members is reduced because of the slippage between concrete and FRP.…”

“…Generally, we can classify FRP systems into two categories: externally bonded reinforcement (EBR), when FRP sheets, plates, or strips are bonded to the surface of the concrete; and near-surfacemounted (NSM), when circular or rectangular FRP bars or strips are installed and bonded in the grooves of the concrete surface. [19][20][21][22][23][24][25][26][27][28][29][30] Seven typical failure modes could be distinguished for RC structures strengthened with FRP: 18 (1) flexural failure caused by FRP rupture, (2) flexural failure caused by crushing of compressive concrete, (3) shear failure, (4) separation of concrete cover of tensile reinforcement, (5) interfacial debonding in FRP plate end, (6) interfacial debonding caused by flexural crack in midspan of the beam, and (7) interfacial debonding caused by intermediate flexural shear crack. Failure mode caused by FRP rupture (mode 1) is appreciated, because, in such case, the full strength of FRP would be used.…”