Strengthening of Fibre Reinforced Concrete Elements: Synergy of the Fibres and External Sheet

TLDR

Structural rehabilitation must accommodate higher loads while preserving member size, and durability is improved by mitigating cracking and corrosion, with fibres offering a prominent solution that reduces cracking and increases mechanical resistance. The study investigates the synergistic effect of steel fibres and external CFRP sheets on strengthening and evaluates their impact on fire limit state performance. The authors employed FRP reinforcing bars, discrete steel fibres, and externally bonded or mechanically fastened FRP sheets in various combinations to assess the synergy. Steel fibres control cracking, alter failure mode, and enhance flexural resistance, while the combined FRP and steel fibre system effectively eliminates corrosion‑induced safety problems.

Abstract

In structural rehabilitation and strengthening, the structural members are often required to cope with larger design loading due to the upgrading of building services and design standard, while maintaining the member size to preserve the architectural dimensions and headroom. Moreover, durability enhancement by mitigating or eliminating the reinforcement corrosion problem is often desired. Concrete cracking is a major initiating and accelerating factor of the corrosion of steel reinforcement. The application of fibres is a prominent solution to the cracking problem. Furthermore, the fibres can increase the mechanical resistance of the strengthening systems. This study reveals the synergy effect of the combined application of steel fibres and external carbon fibre-reinforced polymer (CFRP) sheets. The investigation encompasses the use of fibre-reinforced polymer (FRP) reinforcing bars, discrete steel fibres, externally bonded and mechanically fastened FRP sheets in different combinations. It is discovered that the steel fibres can help to control concrete cracking and eventually alter the failure mode and enhance the flexural resistance. The FRP reinforcement system, together with the steel fibres, radically resolves the structural safety problem caused by corrosion of the steel bar reinforcement. Finally, the impact of the external sheet on the fire limit state performance needs to be resolved, such as by adopting fire protection rendering for the finishes layer.