Thermomechanical Analysis of Reinforced Concrete Beams Under Fire Situation: A Comparison Between Conventional Concrete and UHPC

Ultra-High-Performance Concrete (UHPC) is known for its remarkable durability and strength, owing to its dense microstructure. However, its reduced porosity poses challenges when exposed to high temperatures, making it vulnerable to fire damage compared to conventional concrete. This paper presents thermomechanical numerical simulations of reinforced concrete beams, focusing on understanding the behavior of UHPC and conventional concrete under elevated temperatures. We employed the software ABAQUS and validated thermomechanical properties obtained by experimental tests without occurrence of spalling available on literature. Beams with equivalent strength were modeled, subjected to mechanical loads, and heated following the ISO 834 fire curve. A parametric study was conducted to investigate the influence of the applied load level, concrete cover and compression strength on the behavior of the UHPC. Results showed that UHPC beams heated up significantly faster, reaching temperatures \(\hbox {182}\,^{\circ }\)C higher than conventional concrete beams after 180 min. This faster heating leads to greater displacements and reduced fire resistance, with UHPC beams achieving about 30 min less of resistance. However, further experimental research is recommended to confirm these results and refine the properties of UHPC. From the parametric analyses, we observed that improving the concrete’s strength led to a resistance increase of only up to 5%. Improved results were achieved with the addition of concrete cover. With load increases of 15% and 25%, the resistance decreased by 17.2% and 27.1%, respectively. These results emphasize the importance of considering concrete type in fire safety design, allowing for the definition of appropriate parameters for fire safety standards.