Reinforced concrete Tunnels Exposed to Fire: Effects of Geometry and Fire Curve

Fire represents a severe condition for tunnels due to (a) the geometric features of the compartment which favours the achievement of very high temperatures and makes the intervention by fire brigades difficult, (b) the structural redundancy leading to significant indirect actions, and (c) the sizable sensitivity to fire spalling due to the relevant compression generally characterizing the lining. Repair time and cost past the fire are also critical issues, since the revenue loss connected to traffic disruption must also be considered. Within this context, this paper addresses the effect of structural choices in tunnel fire resistance, by comparing the performance of two different solutions: (1) cast-in-situ and (2) pre-cast segmental tunnel linings. To this aim, finite element analyses have been performed, proving that (I) increasing thickness and redundancy does not necessarily lead to a higher safety factor and (II) fire cooling phase (if any) must be properly taken into account.