Design-oriented assessment of the residual post-fire bearing capacity of precast fiber reinforced concrete tunnel linings

This study presents a meso-scale experimental program and employs a numerical approach to determine the bearing capacity of steel fiber reinforced concretes (SFRC) tunnel linings after fire exposure. First, the effect of temperature on the mechanical properties of SFRC was determined through a refined experimental campaign. Additionally, the suitability of the bending test and the DEWS test to assess the post-fire tensile properties of the SFRC was verified. Then, a thermo-mechanical model was implemented to assess the changes in the bearing capacity of SFRC for tunnels built with TBM technology. Results show that the thermo-mechanical model properly estimated the temperature distribution and the mechanical properties as a function of the duration of fire (t) and depth (z). The bearing capacity of the SFRC segments exposed to the ISO 834 and HFC fire curves were comparable when the condition t ISO = 2 t HFC was satisfied. Additionally, a greater bearing capacity reduction was numerically observed when the compressive region of the cross-section is affected by fire. The results obtained aid in the definition of appropriate rehabilitation operations, classifying the degree of damage sustained by the structure, and provides a procedure for designers regarding the effect of fire on SFRC structures.