The effect of length and inclination of carbon fiber reinforced polymer laminates on shear capacity of near‐surface mounted retrofitted reinforced concrete beams

Abstract

This study undertakes a comprehensive investigation of the shear behavior of reinforced concrete (RC) beams strengthened by near surface mounted (NSM) carbon fiber reinforced polymer (CFRP) laminates. Different strengthening configurations were employed by varying the length and inclination angle of the CFRP laminates. Results indicated that NSM‐CFRP strengthening increased the load‐carrying capacity, ductility, stiffness, and toughness from 8% to 41%, 9% to 78%, 24% to 159%, and 22% to 254%, respectively. Results also confirmed that as the CFRP laminate length decreases, the efficacy of the strengthening process increases, where the load‐carrying capacity, ductility, stiffness, and toughness improved from 8% to 19%, 10% to 21%, 8% to 68%, and 26% to 119%, respectively. Also, the comparative results revealed that specimens strengthened with 45°‐inclined CFRP laminates versus those strengthened with vertical laminates had higher load‐carrying capacity (2%–10%), ductility (1%–35%), stiffness (24%–40%), and toughness (13%–32%). Two analytical formulations to predict the contribution of the possible distinct NSM‐CFRP shear strengthening configurations for the shear resistance of RC beams were considered. Results indicated an agreement between the experimental and the analytical results for both formulas, where the average values for the safety factor, k, ()k=Vtana/Vtexp were 0.80 and 0.73, with corresponding values of standard deviation of 0.195 and 0.125, respectively.

A review on performance of near‐surface mounted‐carbon fiber‐reinforced polymer laminates bonded into slits

“…The explanation can be that initiated cracks meet a smoother surface which helps in delaying the crack propagation. [ 54 ] The main failure mechanism in studies has been reported with increasing deflections, crack widths, and debonding due to poor adhesion of CFRP strips to concrete cover. [ 32,81 ] Also, it is observed that the failure in NSM‐CFRP strengthening scheme occurs as a consequence of poor material, geometry, spacing, and placement patterns of material and grooves cut on the surface.…”

“…It is observed that inclined rods in the NSM-CFRP technique of retrofit are found to be more effective in enhancing the shear capacity of RC beams. [41,42,54] The position of the beams with different inclination angles of the CFRP laminates is shown in Figure 2. An experimental investigation on the concrete beams of size 150 Â 250 Â 1400 mm has shown improved shear behavior after application of CFRP NSM strips at the side cover with trapezoidal, parabolic, and straight profile using electric drill.…”

“…Ibrahim, Wakjira, and Ebead 2020 [68] Al-Zu'bi et al 2021 [54] Shear enhancement of RC beams Analytical formulas for deriving NSM-FRP contribution in shear capacity from Dias and Barros [69] and Nanni et al [ on their surface has given outstanding bond enhancement when tested against pull-out forces. [97] The free end of the FRP can be inserted into the epoxy adhesive to avoid potential slippage during the direct pull out test (DPT).…”

Nonlinear numerical simulation and experimental verification of bondline strength of CFRP strips embedded in concrete for NSM strengthening applications

“…A parametric study on flexural performance and failure modes of NSM CFRP-strengthened concrete beams was performed by Haddad and Almomani. 27 The effect of length and fiber orientation of CFRP laminates on shear behavior of NSM F I G U R E 1 Typical application of NSM composites for strengthening reinforced concrete members retrofitted RC beams was investigated by Al-Zu'bi et al 28 Eljufout and Toutanji 29 investigated fatigue behavior of CFRP-NSM retrofitted RC beams. A comprehensive review on applications of NSM for RC structural members was reported by Al-Saadi et al 30 Validation case studies on performance of RC bridges strengthened by NSM composites are discussed by Lee et al, 31 and Yang, et al 32 Recently, Kamonna and Abd Al-Sada 33 presented results of an experimental study on performance of one-way RC slabs strengthened with near surface mounted bars.…”

“…A parametric study on flexural performance and failure modes of NSM CFRP‐strengthened concrete beams was performed by Haddad and Almomani 27 . The effect of length and fiber orientation of CFRP laminates on shear behavior of NSM retrofitted RC beams was investigated by Al‐Zu'bi et al 28 Eljufout and Toutanji 29 investigated fatigue behavior of CFRP‐NSM retrofitted RC beams. A comprehensive review on applications of NSM for RC structural members was reported by Al‐Saadi et al 30 …”