# Making a Case for Hybrid GFRP-Steel Reinforcement System in Concrete Beams: An Overview
## 5 Conclusions  
GFRP reinforcements are a potential alternative to steel rebars for durable and corrosion-free structures. Though design codes exist for the use of GFRP in RCs, there is scope to address their lack of ductility with the addition of steel reinforcement. This paper has overviewed the research carried out to advance the design of a hybrid GFRP-steel reinforcement system for concrete beams. The primary focus was given to the studies conducted on analytical models that considered mechanical and physical effects to enhance the performance of flexure beams. The main conclusions are summarised as follows:  
* The inherent corrosive nature of steel is a threat to the durability of RC structures, specifically in aggressive environments. The FRPs, which has high strength-to-weight ratio than steel, are one of the most suitable solution to enhance the durability of RC structures.
* GFRP is an economically viable option for the usual commercial applications. Although its properties are not as competent as other FRP variants such as CFRP and BFRP, it is proven to be more efficient than using conventional steel bars, especially in harsh environments.
* Lack of ductility is one of the characteristic traits that questions the application of GFRP bars in flexure beams, where flexural yield is a demanding behaviour to design safe structures. Despite proposing new parameters to quantify the ductility of GFRP-steel RC beams, the studies explaining the synergetic mechanism between the GFRP and steel is very limited.
* The crack developments in the hybrid beams are highly dependable on the bond coefficient used in the design. Hence, it is important to understand the bond behaviour between the GFRP bars used in the hybrid system.
* Most of the flexural beams that experimented with the GFRP-steel hybrid reinforcement system has reported a combined failure mode of steel yielding and concrete crushing. This indicates the activation of the yield behaviour of steel bars before the (rupture) failure of GFRP in the system, which gives the confidence to consider a hybrid reinforcement system for flexure beams.
* In the experimental studies of hybrid GFRP-steel, excessive shear reinforcement has been employed as a strategy to prevent shear failure.
* The attempt to engineer the shear response of hybrid GFRP-steel in RC led to a notable improvement in the performance of flexure-shear failures with a minimal amount of shear cracks and shear crack widths.
* The weakness of GFRPs in RC is in its susceptibility to thermal degradation at comparatively lower temperatures than steel. However, recent studies suggested that this weakness can be mitigated by using adequate concrete cover for increased thermal resistance and applying fire retardants to enhance its performance up to the recommended standard.
* Hybrid GFRP-steel reinforcement is an effective and competitive alternative to steel reinforcement. As identified in this paper, key aspects of their design and structural behaviours must be better understood and require further research to put forward a reliable and sound design procedure.  
Conceptualization, R.D.; Supervision, C.G. and A.O.; data curation, R.D., A.O. and C.G.; writing--review and editing, A.O. and C.G.; writing--original draft preparation, R.D. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.