Experiments on membrane action of composite floors with steel fibre reinforced concrete slab exposed to fire

Abstract

The resistance of composite floor structures traditionally composes of the elemental resistance of the concrete slab and that of the composite beams. The fire resistance of a properly designed floor structure increases due to its membrane behaviour. Its evaluation is based on advanced as well as simple design procedures approved by tests, for partially protected floors reaching 60min and more. Composite structures are increasingly reinforced by steel fibres instead of steel bars. Due to an equal distribution of reinforcement steel fibre reinforced concrete (SFRC) achieves better deformation capacity compared to the traditional reinforced concrete even at elevated temperatures. Therefore, questions have been raised about its fire resistance and utilisation of membrane action of the floor.In the last two years, composite SFRC floor slabs at ambient and at elevated temperature have been tested at the Czech Technical University in Prague. At elevated temperatures, the floor was only partially fire protected. Intermediate beams and SFRC slab in steel sheeting remained unprotected. Concrete slabs were reinforced by steel fibres only without added steel bars. The main aim of the tests was to demonstrate the sufficient properties of the SFRC slab in fire. For the fire resistance of the floor slabs, it is important for the material to have sufficient ductility and adequate tensile and shear strength. These material properties of the SFRC allow for the slab to create a different load bearing mechanism, which increases its fire resistance. Hence, the SFRC slabs have been tested at ambient and at elevated temperature with a focus on ductility and tensile strength of the material.