Novel minimally invasive strengthening method with retrofitted drilled-in FRP longitudinal reinforcement

This paper introduces the world’s first application of Drilled-In Fibre Reinforced Polymer (DI-FRP) as a post-installed longitudinal reinforcement for concrete structure strengthening. This innovative technique represents a transformative advancement over traditional externally applied FRP methods, which often require extensive demolition, produce considerable waste, and face environmental vulnerabilities. By inserting FRP rods directly bonded into drilled holes within the concrete, the DI-FRP method maximizes the tensile strength of FRP with minimal disruption to the strengthened asset. It presents a comprehensive experimental and numerical verification of the DI-FRP method through large-scale bending tests on reinforced concrete beams, showcasing remarkable enhancements in load-bearing and deformation capacity. Notably, the DI-FRP technique achieved more than double the load capacity compared to non-retrofitted specimens (up to a 143% increase). Finite Element Analyses (FEA) further support these findings, underlining the technique's potential. In addition to demonstrating its efficacy, this study outlines a design methodology for DI-FRP, affirming its feasibility as a durable, sustainable, and cost-effective solution for interventions to concrete structures. By establishing DI-FRP as a minimally invasive and high-performance technique, this paper paves the way for future research and applications in structural concrete strengthening. • First application of DI- FRP for longitudinal/flexural concrete structure strengthening. • Minimally invasive technique preserving structural integrity and reducing waste. • DI-FRP method boosts load capacity up to 143% in reinforced concrete beams. • Enhanced deformability and gradual failure improve robustness against extreme loads. • Numerical and experimental validation confirms DI-FRP effectiveness and feasibility