## 4 Conclusions  
In this work, seven manhole specimens were experimentally tested under displacement control up to their rupture. The following variables were investigated: type of fibre-reinforced cementitious material (FRC); type of GFRP grating; depth of the specimens; and top and bottom cover thickness of the GFRP grating. Two types of FRC were considered: mortar reinforced with two types of PAN fibres (PFRM); and concrete reinforced with hooked ends steel fibres and polymer macro-fibres (HFRC). The HFRC presented higher stiffness, compressive strength, and post-cracking tensile capacity than the PFRM. Two types of GFRP gratings were adopted, G_type1 and G_type2, the last one with a higher stiffness and load-carrying capacity. For the depth of the manhole specimens, 80, 100, and 110 mm were considered. Regarding the top cover thickness of the GFRP grating, values between 20 and 50 mm were considered, while, for the bottom cover thickness, values between 0 and 40 mm were adopted. From the experimental program the maximum load (\(P_{max}\)), the centre deflection at this maximum load (\(U_{P_{max}}\)), the initial tangent stiffness (\(K_{Tl}\)) and, based on the maximum load, the corresponding class according to BS EN 124: 1994 [42] were obtained. Based on the obtained results, the following conclusions can be pointed out:  
Figure 16: Force vs. centre deflection of HFRC100_c00_g50 vs. HFRC100_c25_g50. * Regarding the influence of the thickness of the manhole specimens in series made by PFRM, an increase of 20 mm in the thickness (20%) has increased the \(K_{Tl}\) by 54%, and the \(P_{max}\) by 22%. The increase in the thickness was concentrated on the top PFRM cover thickness, demonstrating the influence of this characteristic on the performance of this series of manhole specimens. * By testing manhole specimens of the same thickness but different GFRP gratings and top cover thicknesses in the series with HFRC it was verified that the top HFRC cover thickness had a higher impact on the structural performance than the stiffness and load-carrying capacity of the adopted GFRP gratings. This is a consequence of the dominant punching failure mode. It was verified that an increase from 25 mm to 35 mm on the top HFRC cover thickness has provided an increase of 12% and 53% in the \(P_{max}\) and \(K_{Tl}\), respectively. * The use of FRC instead of PFRM has provided an increase of 69% and 92% in terms of \(P_{max}\) and \(K_{Tl}\), respectively, in the series with manhole specimens of 80 mm depth; while, in the series with manhole specimens of 100 mm depth, the increase in \(P_{max}\) and \(K_{Tl}\) was 121% and 32%, respectively. * In the series made by HFRC, an increase of 20 mm in the manhole specimen thickness (20%) has provided an increase in \(P_{max}\) and \(K_{Tl}\) of 68% and 48%, respectively. This depth increase was exclusively due to the increase in the top HFRC cover thickness, revealing the influence of this parameter. * By taking advantage of the immunity of GFRP to corrosion, the highest structural performance of a manhole specimen is obtained by disposing of the G-type2 with null bottom HFRC cover thickness and the largest possible top HFRC cover thickness. Even for a manhole specimen of 100 mm depth (\(\cong\)24 kg/m\({}^{2}\) of deadweight), its class was D400, which means that it can be installed in the highest loaded zones of a highway. * All manhole specimens failed by punching. Therefore, the stiffness and load-carrying capacity of the tested manhole specimens were dependent on the top concrete cover thickness of the GFRP grating and the type of FRC. In fact, these structural performance indicators have increased with the thickness of the top concrete cover thickness, and with the stiffness and resistance of the FRC. * Since \(K_{Tl}\) and \(P_{max}\) increased significantly with the top concrete cover thickness, this characteristic should be taken into account regarding its favourable repercussion in terms of SLS design verifications for deflection.