Strengthening of RC beams using bottom and side NSM reinforcement

Abstract

The allowable strain in fibre reinforced polymers reinforcement is limited by design codes to avoid debonding. The near-surface mounted (NSM) reinforcement technique has been proven to produce better anchorage behaviour compared to externally bonded reinforcement solutions. However, NSM solutions do not always eliminate debonding issues, with concrete cover detachment (CCD) typically occurring in RC beams strengthened for flexure. This experimental study investigated the efficiency of side mounted (S) compared to bottom mounted (B) NSM bars to prevent CCD. The experimental results were compared to models available in the literature that predict the observed failure modes and the crack spacing in the NSM anchorage zone. Compared to B-NSM, the S-NSM solution was successful in avoiding brittle CCD failure and showed increased rotational capacity and energy dissipation at failure. Existing CCD debonding models were found to be conservative.

Experimental and numerical investigation on low-strength RC beams strengthened with side or bottom near surface mounted FRP rods

“…To date, only a few studies have investigated the performance of side NSM FRP strengthening as that shown in Figure 1(d) (Hosen et al 2017;Hosen et al, 2018;Hosen et al, 2015;Imjai et al, 2020;Sabau et al, 2018;Sharaky et al, 2017;Shukri et al, 2016), and none of these studies has reported results from low-strength RC elements.…”

Performances, challenges and opportunities in strengthening reinforced concrete structures by using FRPs – A state-of-the-art review

“…Similarly, the most common debonding failure observed in NSM systems is cover separation [134] (Fig. 14).…”

“…14). A side-NSM strengthened beam fails through concrete crushing with intermediate crack-induced debonding, which is ductile, compared to the concrete cover separation observed in a bottom NSM system [134]. The smooth surfaces of the NSM strips can result in lower adhesion between the strip and adhesives.…”

Activated Ductile CFRP NSMR Strengthening

“…Pultruded carbon fiber-reinforced polymers (CFRPs) for near-surface mounted reinforcement (NSMR), as a means to strengthen concrete structures, has been used for several decades (e.g., [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ]). The strengthening often results in a significant amount of benefits, namely lower additional permanent loads (CFRP is ~80% lighter than steel), possibility of mobilizing higher tensile strength (CFRP systems are approximately five times stronger than steel), excellent durability properties, installation easiness, among others.…”