Explosive spalling in Reinforced concrete tunnels exposed to fire: experimental assessment and numerical modelling

F Lo Monte, R Felicetti (Politecnico di Milano); A Meda (Univ. degli studi di Roma Tor Vergata); A Bortolussi (Bakaert Maccaferri Underground Solutions)

Fire is a severe scenario for tunnels, since high temperature induces both the decay of mechanical properties and the rise of indirect actions. Furthermore, explosive spalling can take place in concrete (namely, the violent expulsion of shards from the exposed face), with a relevant impact in fire resistance and in the retrofitting phase after the fire. Hence, preliminary screening of concretes before construction plays a key role to reduce spalling risk with the optimal compromise between costs and efficacy. In this context, three test setups were adopted for the assessment of spalling sensitivity in concrete: hot spot, biaxial loading and full-scale tests. The experimental campaign is presented with the aim of explaining the different results. Afterwards, on the basis of the experimental evidence, it is briefly described how to implement a finite element model of a tunnel lining with precast R/C segments, in order to assess the fire resistance taking spalling phenomenon into account.

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