Flexural strengthening of concrete beams with near-surface mounted steel–fiber-reinforced polymer composite bars

Abstract

This article presents an experimental study on concrete beams strengthened with NSM reinforcements under monotonic static loading. The NSM reinforcements include commonly used steel bars, CFRP bars, and four different types of SFCBs. The main parameters of SFCBs considered in this study have been the types of FRP used (CFRP and basalt FRP) and steel/FRP ratio. The results show that (1) the stiffness during the elastic stage and the load capacity at the ultimate state of concrete beams strengthened with NSM-SFCB could be enhanced significantly; (2) the failure modes of the two concrete beams were as follows: the concrete beam strengthened with ordinary steel bar crushed after the steel bar yielded, while the beam strengthened with CFRP bar demonstrated a debonding of concrete cover on the beam soffit without any crushing of the concrete in the compression zone; (3) the steel/FRP ratio is of vital importance for the performance of beams strengthened with NSM-SFCBs. For SFCB with a high FRP/steel ratio, debonding of the concrete cover occurred after the yielding of the SFCB inner steel bars, while for beams strengthened with NSM SFCB with lower FRP/steel ratio, concrete crushing occurred after the rupture of the SFCB outer FRP; (4) compared with NSM-CFRP bars, NSM-SFCB can achieve the same anticorrosion properties at a much lower cost, which makes SFCB a competitive material for NSM strengthening of concrete structures.

Effect of concrete cover thickness and main reinforcement ratio on flexural behavior of RC beams strengthened by NSM-GFRP bars

“…Over the last twenty years, a great deal of research was deployed to the behavior and flexural strength of RC members strengthened by NSM FRP rods. Previous studies focuses on many aspects of the behavior of RC beams strengthened NSM GFRP rods such as ultimate flexural and shear capacities, ultimate deflection and the failure modes [6][7][8][9][10][11][12][13][14][15]. Furthermore, A lot of laboratory experimental works were carried out to explore the bonding behavior between NSM FRP bars and concrete, the effect of FRP anchorage system, NSM FRP length, type of epoxy, dimensions of grooves, size, shape, and type of rebars and concrete strength [16][17][18][19][20][21].…”

Experimental and analytical investigation into the flexural performance of RC beams with partially and fully bonded NSM FRP bars/strips

“…But it also has some disadvantages [25][26][27]. These include only a limited improvement in stiffness when concrete beams are strengthened with glass FRP (GFRP) and aramid FRP (AFRP) as NSM, due to their lower modulus of elasticity; the low strength efficiency of the FRP bars due to bar pullout failure or concrete cover separation as reported in [2] for beams strengthened with CFRP bars; and the high price of FRP considering the advantage obtained from strengthening with NSM bars [27].…”

Punching Strengthening of Concrete Slab-column Connections Using Near Surface Mounted (NSM) Carbon Fiber Reinforced Polymer (CFRP) Bars

“…In addition, the concrete cover and adhesive material protect the reinforcing bars from temperature, vandalism, and damage. Several researches investigated the rehabilitation and strengthening of RC beams and slabs in flexure by NSM technique using FRP bars [12][13][14][15][16]. Another researches investigated the shear performance of RC beams strengthened by the NSM technique using FRP bars in the form of external stirrups [17][18][19][20].…”