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Shear and anchorage behaviour of fire exposed hollow core slabs

Joris Fellinger1, Jan Stark2 and Joost Walraven2
1 TNO Centre for Fire Research, Delft, the Netherlands
2 Delft University of Technology, Faculty of Civil Engineering and Geosciences, Delft, the Netherlands

The fire resistance of hollow core slabs is currently assessed considering flexural failure only. However, fire tests showed that shear or anchorage failure can also govern the load bearing behaviour. As the shear and anchorage capacity of these slabs rely on the tensile strength of the concrete, the load bearing capacity with respect to these failure modes decreases dramatically during fire due to the impact of thermal stresses. This paper presents a FE model for the shear and anchorage behaviour of fire exposed hollow core slabs, comprising new constitutive models for concrete and bond of prestressing strands at high temperatures. The constitutive models were calibrated with 60 new small scale tests carried out at elevated temperatures up to 600 C. The FE model was validated on the basis of 25 full scale fire tests on hollow core slabs loaded in shear. Finally, a parameter study was carried out with the FE model. The results showed that the thermal expansion of concrete, the ductility of concrete in tension and the restraint against thermal expansion by the supports are the main influencing factors. It is recommended to control these factors in design in order to improve the safety level. This paper is an extended summary of the dissertation by the first author.

Key words: Fire resistance, shear failure anchorage failure, bond, prestressing strand, finite element modelling