Numerical model for tracing the response of Ultra-High performance concrete beams exposed to fire

This paper presents a numerical procedure for evaluating the thermo-mechanical response of Ultra-High Performance Concrete (UHPC) beams exposed to fire. The numerical model is based on a macroscopic finite element formulation and utilizes sectional moment-curvature relations to trace the response of UHPC beams from the linear elastic stage to collapse under combined effects of fire and structural loading. Fire-induced spalling, temperature-dependent properties of concrete and steel reinforcement, and realistic failure criteria are incorporated into the analysis. Specifically, an advanced analysis approach for evaluating spalling is incorporated in the model by considering the stresses arising from the combined effects of thermal gradients, structural loading, and pore pressure generated in the concrete section. Comparisons of the predictions from the model with data from fire resistance experiments show a good correlation, indicating the proposed model can reliably predict the thermo-mechanical response, including the extent of spalling in UHPC beams subjected to fire exposure. The applicability of the model for undertaking advanced analysis is shown by conducting a case study to illustrate the influence of load level and fire scenario on the fire response of the UHPC beams.