Behaviour of FRP reinforced RC frames under in-plane loading

Fiber Reinforced Polymers (FRP) have been extensively investigated and successfully implemented as internal reinforcement in new reinforced concrete (RC) elements, including slabs, beams, bridges, and multi-storey car parks, as a means to mitigate the corrosion issues associated with steel reinforcement. However, the linear-elastic behaviour, brittle failure mode, and low modulus of elasticity of FRP rebars raise concerns regarding their ability to provide adequate energy dissipation in seismic zones, limiting their application in earthquake-resistant RC structures such as moment-resisting frames. The behaviour of FRP-reinforced concrete frames under seismic loading remains in the early stages of research, with only limited studies investigating their response to cyclic in-plane loading. Consequently, current design codes do not provide explicit guidance for the use of FRP reinforcement in RC moment frames.

This study aims to address this gap by investigating the seismic behaviour of Glass Fiber Reinforced Polymer (GFRP)-reinforced RC frames subjected to in-plane cyclic loading. A total of six 1/3-scaled RC frames were designed, constructed, and tested under reversed cyclic loading to simulate seismic conditions. Three frames were reinforced with GFRP bent bars, while the remaining three served as steel-reinforced control specimens. The experiments were conducted in displacement-controlled mode, following the loading protocol outlined in ACI 374.1-05. Key test parameters included the longitudinal reinforcement ratio and arrangement in the columns, as well as the presence of transverse reinforcement in the beam-column joints.

The experimental results are analysed in terms of hysteretic response, lateral load-drift behaviour, stiffness degradation, and cumulative energy dissipation to assess the feasibility of GFRP reinforcement in seismic applications. All GFRP-reinforced frames successfully sustained drift levels of up to 2.75%. While the energy dissipation of GFRP-reinforced specimens was initially lower compared to steel-reinforced samples, it increased at higher drift levels. The GFRP frames demonstrated comparable load-bearing capacity to their steel-reinforced counterparts, with one GFRP specimen exhibiting even greater strength. Additionally, the ultimate loads in GFRP frames were reached at higher displacement levels compared to steel frames, indicating their potential to sustain large deformations.

The findings of this study contribute to the ongoing efforts to evaluate the seismic viability of GFRP-reinforced RC frames and provide essential data for the development of future seismic design provisions for FRP-reinforced structures.