Bond of NSM FRP-Strengthened Concrete: Round Robin Test Initiative

Abstract

Despite the extensive research that has been conducted on the debonding behaviour of FRP strengthening systems, no standard methodology has been yet established on its experimental characterization. In this context, to assess the performance and reliability of small scale testing Page 2 of 46 on NSM (near surface mounted) FRP strengthening systems, an experimental program was carried out on a series of nine NSM FRP strengthening systems, in the framework of an international Round Robin Testing (RRT). Eleven laboratories and seven manufacturers and suppliers participated in this extensive international exercise, which regarded both NSM and EBR FRP strengthening systems. Test results obtained for the NSM systems by the participating laboratories are discussed and compared in this paper to investigate the feasibility of the adopted single/double pulling shear test method, to investigate the mechanism of bond between NSM FRP reinforcement and concrete, and to investigate the level of variability obtained between the participating laboratories testing the same material batches. It is concluded that the tested variants in the adopted single/double shear pulling test have a significant influence, stressing the importance of the level of detail of standardized test protocols for bond verification. On overall, given the variants included in this study, the obtained variation in bond stress-slip behaviour between the laboratories remained fairly limited.

Characterization and Simulation of the Bond Response of NSM FRP Reinforcement in Concrete

“…The values of the parameters that define the different local bond-slip laws, as well as the properties of materials and characteristics of specimens have been chosen according to previous experimental campaigns found in the literature [13][14][15][16]25,26], with the aim to simulate conditions as realistically as possible.…”

“…In those bond-slip laws with a friction branch, G f is calculated according to Haskett et al [27], as the area under the ascending and descending stages of the bond-slip law, without taking into account the friction stage, as illustrated in Figure 5. A value of 8.5 N/mm has been set for G f in all the models [16,25,26]. The comparison between the studied bond-slip laws is shown in Figure 6.…”

A Parametric Study on the Flexural Strengthening of Reinforced Concrete Beams with Near Surface Mounted FRP Bars

“…Hence, a great number of researchers have studied the effective factors affecting the efficiency of application FRP with different techniques like NSM and EBR via various methods and solutions. Experimental studies of Al-Mahmoud et al [14], Barros and Fortes [15] Bilotta et al [6,7,9], Grace et al [2], Lee et al [16], Lu et al [17], Novidis et al [13], Rizzo, and De Lorenzis [18], Sharaky et al [11,[19][20][21], Tang et al [22], Wang et al [23], Wu et al [24] and numerical analyses of Bianco et al [25,26], Coelho et al [27], Hawileh [28], Kara et al [29], Kaveh et al [30], Seo et al [31], Sharaky et al [20], Teng et al [32], Zhang et al [33] are some of the most recent and pioneer studies in the field of strengthening existing structures with FRP according to the near surface mounted (NSM). Despite the fact that innumerable recent studies devoted at appraising the potentialities of strengthening existing structures with FRP, nevertheless limited design guidelines are currently available for either the externally bonded reinforcement or near surface mounted strengthening technique.…”

“…Over the several last decades, strengthening of existing structures including reinforced concrete beams, slabs, walls and columns through the externally bonded reinforcement (EBR) and the near surface mounted (NSM) methods with fiber reinforced polymer (FRP) has been successfully utilized in civil engineering applications due to its efficiency, effectiveness and ease of application for strengthening concrete structures in both flexure and shear. A laminate or textile bond onto the surface of concrete elements in externally bonded method (EPR) while the near surface mounted method consists of placing fiber reinforced polymer bars into grooves precut on the concrete members and embedding them with a high-strength adhesive [6]. The efficiency of using FRP for strengthening of reinforced members according to the near surface mounted (NSM) method is widely proven in comparison to the externally bonded reinforcement (EBR) due to the fact that, the tensile strength of fiber reinforced polymer is better exploited [7].…”

Seismic Behavior of Substandard RC Columns Retrofitted with Embedded Aramid Fiber Reinforced Polymer (AFRP) Reinforcement

“…FRPs are also utilized as external tendons for strengthening concrete structures [7][8][9]. While there are many studies on external confinement of columns or joints [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], and on flexural retrofit with near surface mounted (NSM) FRP rods or pultruded strips under monotonic loading conditions [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42], only few studies are available on flexural retrofitting using FRPs under repeated loading conditions [43][44][45]. According to the best knowledge of the authors', reversed cyclic flexural behavior of RC members strengthened with longitudinal FRP reinforcement was studied for the first time by Ilki and Kumbasar [46].…”