Numerical analysis of fire exposed ultra-high performance concrete (UHPC) columns

Due to higher aesthetical requirements for the load bearing structure, an increasing amount of slender components is used. The ongoing research and development in concrete technology yields to the possibility to process this slender components out of ultra-high performance concrete (UHPC). Compared to normal strength concrete, the high packing density and the addition of steel fibres leads to a high compressive strength and ductile behavior. In case of fire protection, these material properties and slender dimensions are disadvantageous, because the high packing density leads to high pore pressure and concrete spalling when the remaining water content is evaporating. The higher surface to volume ratio of slender components additionally leads to higher temperatures and reduced load bearing capacity in case of fire. During the research project "Theoretical and experimental determination of the high temperature behavior of ultra high performance concrete (UHPC)" of the priority program 1182, funded by the Deutsche Forschungsgemeinschaft, two general UHPC mixtures were developed. The prevention of explosive spalling was achived by adding polypropylen fibres. Furthermore, the thermal and mechanical material propertiers were assessed in small-scale experiments. To validate the material properties and check the model capabilities, four large-scale experiments were conducted assessing the load bearing capacity of UHPC columns exposed to fire. In this paper, the numerical modelling of the structural behavior of fire-exposed UHPC-columns with finite element method is depicted. The model is compared with the experimental results.