Matthias Siemon, Jochen Zehfuß


The research activity in progress and the advancements in concrete technology are leading to an increased use of high performance and ultra high performance concrete in structural engineering. Due to its high compressive strength and ductile behavior in combination with steel fibres, UHPC structural members can be designed as slender and light structures compared to standard concrete design. This increasingly leads to the option in architectural design to highlight the bearing capacity of the building without hiding the structural components.

In case of fire safety design a disadvantageous behavior of UHPC compared to normal strength concrete is well known and documented. The high packing density of the cement matrix is the main reason for explosive spalling behavior when exposed to fire. To avoid spalling, an appropriate amount of polypropylene fibres has to be introduced in the concrete mix design. In addition, slender and light structures are in general more sensitive to fire exposure due to the higher surface to volume ratio.

In this paper, the analysis of the thermal and mechanical material properties using experimental and numerical methods is presented. The investigations were carried out during the priority program 1182 in the research project “Theoretical and experimental determination of the high temperature behavior of ultra high performance concrete (UHPC)”, funded by the German Research Foundation (DFG), see (Schmidt 2014) and (Hosser et al. 2014).

In the project the thermal properties heat conductivity, specific heat capacity and the temperature dependent density as well as the mechanical properties like the temperature dependent stress-strain-relation and thermal expansion were experimentally determined. In addition, the optimum fibre content was determined. The findings of the project were used to develop a material model and checked against experimental results on fire exposed UHPC columns using a FE model.


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