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<p>Recently, fiber-reinforced polymer (FRP) has seen increased use as both reinforcement and retrofitting material in various concrete structures. FRP materials offer advantages such as corrosion resistance, durability, and a high strength-to-weight ratio. Due to these benefits, FRP is viewed as a promising alternative to traditional steel reinforcement and as an effective strengthening solution for existing structures that require maintenance or repair because of harsh environmental conditions, increased service loads, design or construction flaws, or structural damage. Extensive research has focused on strengthening and reinforcing reinforced concrete (RC) beams with carbon fiber-reinforced polymer (CFRP), especially through external CFRP bars and sheets using either direct bonding or near-surface mounted (NSM) techniques. Different types of FRP have also been studied as primary reinforcement in concrete and as external strengthening systems for RC beams. However, there is still a lack of comparable studies on glass fiber-reinforced polymer (GFRP). This study uses the NSM technique to improve the flexural capacity of RC beams and to explore the potential of GFRP bars as a replacement for steel reinforcement under flexural loads. Four beams were tested with a 500&#xa0;kN capacity hydraulic jack in a three-point bending setup, with hinged and roller supports. All specimens had the same dimensions: 170&#xa0;mm (width), 260&#xa0;mm (height), and 1600&#xa0;mm (length), and were tested until failure. The main variables were reinforcement type (steel versus GFRP) and the diameter of the strengthening bars. Responses measured included ultimate load, cracking load, crack width, load–displacement behavior, and elongation. Results were validated according to the ACI 440.2R-17 code. Among the specimens, one served as a control with internal steel reinforcement (CBSR), while another used internal GFRP reinforcement instead of steel (CBFR). A third included an external GFRP NSM bar along with internal steel reinforcement (SBBG1B), and the fourth combined an external GFRP NSM bar with internal GFRP reinforcement (SBFG1B). The findings showed that the highest flexural capacity was achieved by specimen SBFG1B. Replacing longitudinal steel reinforcement with GFRP increased the failure load and crack widths but decreased ductility, energy absorption, and strain-hardening capacity. Additionally, increasing the concrete’s compressive strength was more effective when combined with GFRP bar reinforcement.</p>

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Experimental investigation of RC beams reinforced with GFRP bars and strengthened using the NSM technique: flexural performance

  • 期刊论文

  • 发表日期：

    2025年11月25日

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  • E. A. Hassan,
  • M. S. Zahran,
  • A. Osman,
  • Nabil M. Nagy

摘要

Recently, fiber-reinforced polymer (FRP) has seen increased use as both reinforcement and retrofitting material in various concrete structures. FRP materials offer advantages such as corrosion resistance, durability, and a high strength-to-weight ratio. Due to these benefits, FRP is viewed as a promising alternative to traditional steel reinforcement and as an effective strengthening solution for existing structures that require maintenance or repair because of harsh environmental conditions, increased service loads, design or construction flaws, or structural damage. Extensive research has focused on strengthening and reinforcing reinforced concrete (RC) beams with carbon fiber-reinforced polymer (CFRP), especially through external CFRP bars and sheets using either direct bonding or near-surface mounted (NSM) techniques. Different types of FRP have also been studied as primary reinforcement in concrete and as external strengthening systems for RC beams. However, there is still a lack of comparable studies on glass fiber-reinforced polymer (GFRP). This study uses the NSM technique to improve the flexural capacity of RC beams and to explore the potential of GFRP bars as a replacement for steel reinforcement under flexural loads. Four beams were tested with a 500 kN capacity hydraulic jack in a three-point bending setup, with hinged and roller supports. All specimens had the same dimensions: 170 mm (width), 260 mm (height), and 1600 mm (length), and were tested until failure. The main variables were reinforcement type (steel versus GFRP) and the diameter of the strengthening bars. Responses measured included ultimate load, cracking load, crack width, load–displacement behavior, and elongation. Results were validated according to the ACI 440.2R-17 code. Among the specimens, one served as a control with internal steel reinforcement (CBSR), while another used internal GFRP reinforcement instead of steel (CBFR). A third included an external GFRP NSM bar along with internal steel reinforcement (SBBG1B), and the fourth combined an external GFRP NSM bar with internal GFRP reinforcement (SBFG1B). The findings showed that the highest flexural capacity was achieved by specimen SBFG1B. Replacing longitudinal steel reinforcement with GFRP increased the failure load and crack widths but decreased ductility, energy absorption, and strain-hardening capacity. Additionally, increasing the concrete’s compressive strength was more effective when combined with GFRP bar reinforcement.