Near surface mounted CFRP laminates for shear strengthening of concrete beams

Abstract

A Near Surface Mounted (NSM) strengthening technique was developed to increase the shear resistance of concrete beams. The NSM technique is based on fixing, by epoxy adhesive, Carbon Fiber Reinforced Polymer (CFRP) laminates into pre-cut slits opened in the concrete cover of lateral surfaces of the beams. To assess the efficacy of this technique, an experimental program of four-point bending tests was carried out with reinforced concrete beams failing in shear. Each of the four tested series was composed of five beams: without any shear reinforcement; reinforced with steel stirrups; strengthened with strips of wet lay-up CFRP sheets, applied according to the externally bonded reinforcement (EBR) technique; and two beams strengthened with NSM precured laminates of CFRP, one of them with laminates positioned at 90°and the other with laminates positioned at 45°in relation to the beam axis. Influences of the laminate inclination, beam depth and longitudinal tensile steel reinforcement ratio on the efficacy of the strengthening techniques were analyzed. Amongst the CFRP strengthening techniques, the NSM with laminates at 45°was the most effective, not only in terms of increasing beam shear resistance but also in assuring larger deformation capacity at beam failure. The NSM was also faster and easier to apply than the EBR technique. The performance of the ACI and fib analytical formulations for the EBR shear strengthening was appraised. In general, the contribution of the CFRP systems predicted by the analytical formulations was slightly larger than the values registered experimentally. Performance of the formulation by Nanni et al. for NSM strengthening technique was also appraised. Using bond stress and CFRP effective strain values obtained in pullout bending tests with NSM CFRP laminate system, the formulation by Nanni et al. predicted a contribution of this CFRP system for the beam shear resistance of 72% the experimentally recorded values.

Shear Rehabilitation of RC Deep Beams using NSM CFRP Anchor Bars

“…In fact, since the last decade, numerous research on NSM has been conducted by various researchers focusing on strengthening of damage structures in flexure using either CFRP laminates, strips or rods [1][2][3][4][5][6].…”

Performance of NSM-FRP RC beams in flexure and shear using locally developed CFRP rebars

“…It was concluded that all strengthened beams have higher load carrying capacity than the control beams. Barros and Dias (2006) conducted tests on the flexural behaviour of NSM strengthened RC beams using FRP laminates. They studied the influences of the laminate inclination, beam depth and longitudinal tensile steel reinforcement ratio on the efficacy of the strengthening techniques.…”

Near surface mounted FRP reinforcement for strengthening of concrete structures

“…11) firstly the concrete was removed from the non-linear hinge region (100-150 mm from the column bottom) and was replaced by epoxy mortar, the groves were cut along the faces subjected to tensile stress and in the alignment of the grooves perforations of about 100 mm were made in the footing to anchor the FRP reinforcement. The test showed a significant increase of the load carrying capacity of both PRE and POS strengthened columns [18].…”

“…Strengthening technique in specimens of RC column [18] To asses effectiveness of NSM strengthening three series of RC columns (non-strengthened columns NON, strengthened with CFRP strips PRE, tested columns of the NON series strengthened with CFRP strips POS) were loaded with static axial compression load and cyclic horizontal load. The strengthening technique presented some particularities (Fig.…”