Experimental investigation of the shear behaviour of RC beams using unidirectional hemp fibre mat-wrapped hybrid steel stirrups

This study presents an experimental insight into the shear behaviour of reinforced concrete (RC) beams using hybrid steel stirrups wrapped with unidirectional hemp fibre mats. Conventional stirrups were modified by epoxy-bonding hemp fibre mats over steel rods at varying wrap lengths, and their influence on beam performance was systematically evaluated. The results demonstrated a remarkable improvement in load-carrying capacity, ductility, and crack resistance compared to conventional beams. The maximum load capacity increased from 132 kN (conventional) to 142 kN (2 cm wrap) and 158 kN (4 cm wrap), reflecting an overall enhancement of 20%. The deflection at peak load improved from 7.1 mm to 10.1 mm and 13.2 mm, indicating an 85% increase in ductility with extended wrapping. Similarly, the initial crack load rose from 40 kN to 49 kN and 55 kN, demonstrating improved crack resistance and stiffness in the hybrid beams. Failure modes revealed a significant transition from sudden brittle failure in conventional beams to gradual and highly ductile failure in wrapped beams, ensuring greater energy dissipation and structural resilience. Notably, the failure displacement nearly doubled, rising from 7.6 mm in conventional beams to 12.8 mm in 4 cm wrapped beams. These findings confirm that hemp fibre wrapping effectively delays shear crack propagation, enhances post-cracking behaviour, and improves ductility, while also offering an eco-friendly alternative to synthetic fibres. The proposed hybridisation technique demonstrates strong potential for sustainable and high-performance structural applications.