Modeling the fire-induced spalling in concrete structures incorporating hydro-thermo-mechanical stresses

This paper presents a numerical approach for predicting spalling in concrete structural members under fire conditions. The proposed approach evaluates spalling by taking into account the stresses generated due to pore pressure, thermal gradients, and structural loading under fire conditions. This approach is incorporated as a spalling sub-model into a macroscopic finite element based model that is capable of tracing the thermo-mechanical response of RC beams from pre-cracking stage to collapse under fire conditions. The analysis predictions, namely temperature, deflection, and extent of spalling are compared against the measured values from full-scale fire resistance tests on RC beams made with different concrete types of varying strengths. Results from the analysis indicate that pore pressure induced stresses are the primary trigger, though thermal and mechanical stress levels exert influence on the occurrence of spalling. Further, the level of spalling significantly influences fire resistance of concrete beams under severe fire exposures, and neglecting fire-induced spalling can lead to un-conservative fire resistance predictions in certain scenarios, specifically in the case of high strength concrete (HSC) and ultra-high performance concrete (UHPC) beams.