## 2 Experimental Program
### Properties of Constituent Materials and Reinforcing Systems
#### 2.4.2 GFR Gratings  
By testing two exemplars of the two types of GFRP gratings according to the setup described in Section 2.3, the load vs. central deflection relationship depicted in Figure 7 was obtained. The results evidenced that the GFRP grating with 50 mm height, G_type2, was as expected, presented a higher stiffness and load-carrying capacity than the GFRP grating with 35 mm height, G_type1, but of smaller deflection at failure. The average maximum load and corresponding deflection of G_type1 was 79 kN and 28 mm, while, in G_type2, the values of 99 kN and 21 mm were obtained.  
Figure 8 shows the typical failure mode registered in these tests. It is verified that the fundamental failure mode is the in-plane delamination due to the inexistence of fibres in the vertical direction of the components forming the grating. It should be noted that the elements of this grid-type structure are subjected to shear forces, bending moments, and some torsional moments. Despite the apparent double symmetry of the testing specimens, geometric imperfections of the tested GFRP gratings introduce some torsional moments, which, combined with shear forces and bending moments, promote the observed failure mode.  
The Young's modulus of the GFRP material constituting these G_type1 and G_type2 was evaluated by inverse analysis, simulating numerically these tests with the version 4.0 of FEMIX computer program [59]. For this purpose, the G_type1 and G_type2 specimens were modelled using 112 plane shell finite elements of eight nodes and 2 by 2 integration points for the evaluation of the membrane, bending, and shear stiffness components, and assuming linear-elastic behaviour for the GFRP (Figure 9). The formulation is based on the Reissner-Mindlin theory, whose implementation in FEMIX is described elsewhere [60]. Loading and support conditions for the specimens were modelled in accordance with the experimental test setup (Figure 4a). By fitting as best as possible the average force-deflection relationship registered in the GFRP gratings with this inverse analysis, a modulus of elasticity of 15 GPa and 11 GPa was obtained for the G_type1 and G_type2, respectively. The decrease in the modulus of elasticity of the GFRP with the increase in the depth of  
Figure 7: Load vs. central deflection of the GFRP gratings G_type1 and G_type2.  
\begin{table}
\begin{tabular}{c c c c c c} \hline  & \(f_{\textit{fcL}}\) [MPa] & \(f_{\textit{R1}}\) [MPa] & \(f_{\textit{R2}}\) [MPa] & \(f_{\textit{R3}}\) [MPa] & \(f_{\textit{R4}}\) [MPa] \\ \hline Average & 13.63 & 13.23 & 13.09 & 11.73 & 10.22 \\ CoV (\%) & 23.6 & 12.45 & 10.76 & 11.06 & 15.89 \\ \hline \end{tabular}
\end{table}
Table 5: Limit of proportionality and residual flexural tensile strength of the developed HFRC.  
the cross-section of the GFRP grating might be a consequence of the larger number of layers required to produce G_type2 over G_type1. Since this layered organization was not simulated numerically, the localization of damage in these interfaces can justify the obtained values; therefore, they should face a modulus of elasticity of the GFRP in the context of assuming the GFRP grating as a linear and isotropic material. More complex simulations could be performed, even considering the elements of the GFRP grating as an assemblage of unidirectional GFRP layers, but the lack of information to simulate the bond conditions between two consecutive layers would mean that this exercise is not useful.