A Preliminary Approach for Accidental Load Design of a Submerged Floating Tube Bridges: Blast-Fire Interaction on RC Slabs

Submerged floating tunnels are more and more considered as a suitable solution to cross water channels limiting environmental impact on the visual landscape and ensuring large ship passage while crossing large distances between coasts. The design of this kind of strategical infrastructures must deal not only with live loads and particular loading condition coming from the floating situation but needs also to carefully consider accidental actions that concur to the global safety of the infrastructure. The construction of the new E39 highway along the Norwegian coast asks for crossing several fjords and this solution is seriously taken into consideration. For this reason, a comprehensive research programme was aimed at the analysis of accidental load design of the infrastructure. This paper aims to present a comprehensive overview of an ad-hoc experimental investigation on the behaviour of reinforced concrete (RC) circular slabs (60 cm diameter) under exposure to fire, blast, or a combination of both actions. Additionally, it seeks to draw design-driven conclusions that could be valuable for the design of critical infrastructure in scenarios involving fire and blast. The presented experimental campaign was intended to provide a benchmark for assessing the reliability of the design approaches to be adopted in the design of the global infrastructure. First, the concrete mechanical characterisation at normal condition and at high temperatures was performed referring both to the uniaxial compression and uniaxial tension. The structural behaviour of simply supported RC slab has been also investigated by considering slabs exposed to a hydrocarbon fire curve at different exposure times and by considering the post-fire application of static or dynamic loading condition. In particular, the fire curve was applied by a gas burner while the dynamic load was reproduced by a shock tube equipment that was used to apply two different blast-like pressure histories.