Experimental Investigation of Hybrid FRP Bonding for Strengthening Steel Plates and Beam Sections under Static Loading

Document Type : Regular Paper

Authors

Department of Civil Engineering, Marwadi University, Rajkot, India

Abstract

This study presents an experimental investigation into the tensile and flexural performance of steel members strengthened using Fiber Reinforced Polymer (FRP) composites, specifically Carbon FRP (CFRP) and Glass FRP (GFRP). Mild steel plates (600 mm × 50 mm × 6 mm) were tested under axial tension, with FRP sheets applied in single-layer (SL) and double-layer (DL) configurations. Strengthening was further enhanced using mechanical anchorage techniques such as grooving and end-plate bolting. For flexural testing, two steel section types, Channel Section (CS) and Rectangular Hollow Section (HS), each 1000 mm in length, were retrofitted with externally bonded CFRP and GFRP sheets and subjected to four-point bending. Key parameters studied include ultimate load, yield strength, initial stiffness, ductility, and energy absorption. The results demonstrate that DL configurations significantly improve both strength and stiffness compared to SL counterparts, while anchorage mechanisms effectively delay debonding and enhance overall structural performance. Among the FRP types, CFRP exhibited higher load capacity, whereas GFRP showed relatively higher ductility in some cases due to better bond distribution. While the findings confirm the effectiveness of FRP strengthening in enhancing structural behavior but still the study is limited by the use of small-scale specimens and simplified boundary conditions, which may affect full-scale generalization. Future work could address long-term durability and field-level performance under varying load conditions.

Graphical Abstract

Experimental Investigation of Hybrid FRP Bonding for Strengthening Steel Plates and Beam Sections under Static Loading

Highlights

  • Hybrid FRP retrofitting enhances structural resilience in steel infrastructure.
  • Double-layer CFRP retrofitting increased tensile strength by over 27%.
  • Grooved steel surfaces enhanced FRP bonding, durability and represents as sustainable retrofit solution.
  • Hybrid anchorage with bolts improved both load capacity and ductility.
  • Flexural strength improved 92% in CFRP-strengthened hollow sections, aligning with better option for steel retrofit solution in safer urban structures.

Keywords

Main Subjects

References

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History

  • Receive Date: 30 May 2025
  • Revise Date: 30 July 2025
  • Accept Date: 17 August 2025

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