# Making a Case for Hybrid GFRP-Steel Reinforcement System in Concrete Beams: An Overview
## 4 Outlook for Future  
The existing research and engineering practices overviewed in this paper elaborate on the huge potential of hybrid GFRP-steel reinforcement systems to meet the durability, strength, and serviceability requirements of most civil engineering applications. The studies agree on the superiority of GFRP rebars in their tensile strength and durability compared to steel reinforcement. Moreover, the hybrid application of GFRP and steel is an effective way to develop ductile responses to GFRP-reinforced beams. However, there is a lack of understanding in specifying and defining the ductility activation in the hybrid GFRP-steel beam systems. A few concepts already exist, but further research is needed to enable the scalability and generalisation of the proposed models. This section discusses these constraints, challenges, and the outlook for future research.  
The concept of hybrid GFRP-steel reinforcement is still in its developing stage. The available research data and information from the out-of-the-lab implementation are building up. There is, however, great need to better understand and predict the failure modes and ultimate states of hybrid reinforcements.  
There is a lot to learn about the concept of ductility, its development and its application to hybrid GFRP-steel RC systems. Whilst many of the proposed design models of hybrid GFRP-steel beams are anticipated to develop into ductile failure modes, these models have been developed based on steel RCs and their calibration conducted with set ratios and the arrangements of reinforcement bars.  
This lack of detailed information on different areas calls for more clarification before the application of GFRP-steel hybrid RC systems can become practice. Hence, the following summarises the topics of interest for future research studies.  
* Investigation of the factors that control the activation of ductile behaviour in steel reinforcement in hybrid reinforcement arrangements.
* Experimental studies on GFRP shear reinforcement (stirrups) incorporated with hybrid reinforcement systems.
* Experimental and numerical studies on the effects of different grades of steel on ductility development in hybrid GFRP-steel RC beams.
* Investigation of the behaviours of hybrid GFRP-steel reinforcement systems to varying temperature gradients and their recovery.
* Investigations on the long-term durability of GFRP bars.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Literature** & \begin{tabular}{c} **Fire Resistance** \\ **Time t (Min)** \\ \end{tabular} & \begin{tabular}{c} **Concrete Cover** \\ **(mm)** \\ \end{tabular} & \
\begin{tabular}{c} **Peak Temperature** \\ **(\({}^{\circ}\)C)** \\ \end{tabular} &
\begin{tabular}{c} **Specimen Model** \\ \end{tabular} & **Fire Model** \\ \hline
[157] & 60 & 64 & 400 & ENV EC2-1992 & ASTM E119-1976 \\ \hline
[158] & 94 & 70 & 377 &
\begin{tabular}{c} ENV EC2-1992 \\ ACI-440-2001 \\ \end{tabular} & BS 476-1987 \\ \hline
[159] & 30 & 50 & 400 &
\begin{tabular}{c} ENV EC2-1992 \\ (Hybrid Steel) \\ \end{tabular} & - \\ \hline
[160] & 45 & 25 & 160 & ISIS Canada-2001 &
\begin{tabular}{c} ASTM E119 \\ ISO 834 \\ \end{tabular} \\ \hline
[148] & 90 & 85 & 225 & - & DIN EN 1363 \\ \hline
[161] & 60 & 20 & 170 & ACI 440.1R-06 & BS EN 1363-1 \\ \hline
[162] & 50 & 20 & 820 &
\begin{tabular}{c} 1-D two-node \\ Composite Beam \\ Element \\ \end{tabular} & ISO 834 \\ \hline
[163] & 120 & 70 & 400 & 3-D nonlinear FE Model & ISO 834 \\ \hline
[164] & 40 & 30 & 500 & ENV EC2-1992 & EC1 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Overview of FE and Experimental studies.  
* Numerical modelling of the effects of bond-slip behaviour of GFRP in hybrid RC systems.
* Experimental and numerical studies of the effects of the surface characteristics of GFRP bars on the structural performance of hybrid RC beams.