## 4 Summary and Conclusions  
The experimental work presented in this paper was aimed at the investigation of the fire resistance of sandwich walls with GFRP connectors. The structural performance of the three one-storey walls was tested under vertical eccentric loading, exposure to fire and subsequent impact load. The thermal and structural performance of the insulation and connectors under high temperatures were analysed. All the REI requirements were met for 120 min of fire loading and impact loading. The connectors in the middle area of Specimens 1 and 3 experienced significant heat-induced damage but were still able to mechanically couple both concrete wythes. In Specim 2, the connectors melted through the entire thickness of the fire-exposed facing wythe. In this case, however, the wall maintained its structural integrity due to the still load-bearing connectors at its perimeter. Due to the potential failure of all the connectors, the application of additional, fire-resistant connectors to support the load-bearing function in the fire situation should be considered. The possible influence of the connectors on the heat-induced spalling of the concrete was analysed. In Test 2, a spalling-prevention effect caused by the melted connectors was observed. The concrete in some areas surrounding the empty holes left by the connectors on the fire-exposed side did not spall during the test, which could suggest that the moisture was able to escape through the voids left by the connectors, lowering the pore pressure in the concrete. Figure 12: Location of the transducers for the measurement of the relative displacement of the facing wythe in the cases of Tests 1 and 3—an example from Test 1. Therefore, it can be concluded that the presence of GFRP connectors did not contribute to the concrete spalling but, on the contrary, had a mitigating influence on the surrounding concrete. The space-enclosing function of the wall was fully maintained and the spread of fire and smoke development were prevented. The moisture enclosed in the wall was brought to boiling and served as a main heat carrier through the insulation at the early stage of the test. This resulted in the heating-up of the entire insulation and the internal side of the wythe not exposed to fire to 100 \({}^{\circ}\)C at almost the same rate for all the specimens. This sudden increase at an early stage of fire exposure should be considered in the application of different temperature-sensitive or combustible materials, since the insulation can be eliminated from thermal and mechanical contributions in this way. The recorded displacement of the unsupported facing wythe showed that the wythes followed the same curvature of heat-induced bowing. This indicates that the connectors maintained their mechanical properties throughout the testing time and were able to maintain a constant distance between the concrete wythes, coupling them together. Additionally, no indication of the potentially dangerous fall-off of the facing wythe in Test 2 was observed. However, the curvature-induced cracking of the wythes not exposed to fire was observed in Test 1 and 3. The structural coupling of the two concrete wythes provided by the shear stiffness of the bar-type connectors and the insulation was observed in all the tests. Even in Test 2, where the connectors in the middle area of the wall were damaged, the facing wythe remained mechanically attached to the load-bearing wythe. This indicates that the mechanical contribution of the core and the facing layers to the flexural stiffness can be significant. The large thermal bowing observed in Tests 1 and 3 suggests that some degree of composite action was maintained throughout the fire testing time and during the mechanical impact loading.