Behavior and failure modes of reinforced concrete beams strengthened with NSM GFRP or aluminum alloy bars

Abstract

Although the use of near‐surface mounted (NSM) fiber reinforced polymer (FRP) reinforcement satisfactorily enhances the flexural capacity of deficient reinforced concrete beams, the concrete beams strengthened with NSM FRPs typically exhibit brittle behavior. Aluminum alloy (AA) bars possess non‐corrosive characteristics like FRPs but also exhibit a nonlinear tensile response with a clear yield point. This paper investigates the failure modes of reinforced concrete beams strengthened with either NSM glass FRP (GFRP) bars or AA bars. A total of six concrete beams including one control beam were tested under four‐point bending. The effects of NSM reinforcement type, internal steel reinforcement ratio, and NSM reinforcement ratio on the failure behavior of the strengthened beams were examined. The ultimate flexural load capacity, ductility index, energy absorption capacity, strains in steel reinforcement and in concrete, and cracking behavior for each tested beam were determined and analyzed. The results indicated that for the same NSM reinforcement ratio, the NSM GFRP bars provided considerably higher increases in the flexural strength of reinforced concrete beams compared to the AA bars. However, the beams strengthened with AA bars showed more ductile response compared to the beams strengthened with NSM GFRP bars.

Crack parameters in normal section of FRP strengthened RC elements

“…The crack width of the beams strengthened with externally bonded CFRP reinforcements (EBR) was measured in I and II stages (see Figure 5). While Xing et al (2018) has established full load-crack width response of the beams strengthened with near surface mounted GFRP reinforcements (NSM) (see Figure 6). There is a strong relation between predicted and experimental bending moment-crack width dependency (coefficient of correlation R = 0.95 ÷ 1.00).…”

“…Numerical results are compared with experimental ones from the tests of 9 RC beams, strengthened with externally bonded (EBR) and near surface mounted (NSM) FRP reinforcements. The experimental results are collected from different scientific publications (Slaitas et al, 2018a;Xing, Chang, & Ozbulut, 2018).…”

Feasibility of using aluminum alloy bars as near‐surface mounted reinforcement for flexural strengthening of reinforced concrete beams

“…This is important because commonly a brittle failure mode was observed in the RC beams strengthened with FRPs. 6,33,41 High deflection capacities and good ductile behavior will provide sufficient warnings before the failure of the strengthened beams. However, for the Specimen AB-1d where the failure occurred due to edge concrete cover splitting, the deflection capacity and the ductility remained at 38.1 mm and 5.01, respectively.…”

Feasibility and flexural behavior of RC beams prestressed with straight unbonded aluminum alloy tendons

“…Main applications of AAs in bridge structures include movable and floatable bridges, replacement of deteriorated bridge decks, and pedestrian bridges (Dey et al, 2016; Siwowski, 2006). In addition, using as strengthening reinforcements, it is authenticated that AAs have attractive properties which can overcome the deficiencies of FRPs in RC beams (Abdalla et al, 2016; Abu-Obeidah et al, 2015; Rasheed et al, 2017; Xing et al, 2018). More recently, the AAs of 6xxx series have also been used as reinforcement in concrete structures (Xing and Ozbulut, 2016).…”