Shear and Anchorage Behaviour of Fire Exposed Hollow Core Slabs

Hollow core (HC) slabs are made of precast concrete with pretensioned strands. These slabs are popular as floor structures in offices and housing. At ambient conditions, the load bearing capacity can be dominated by four different failure modes, i.e. flexure, anchorage, shear compression and shear tension. As the economic production process does not allow for the inclusion of mild reinforcement, the slabs rely on the tensile strength of concrete for the shear and anchorage capacity. When exposed to a fire, the HC slabs have to maintain their load bearing and separating function for a certain time in order to facilitate the fire fighting actions and to provide sufficient time for the users of the building to escape and for rescue teams to search the building. Current design codes consider only flexural failure, while fire tests carried out in the past showed that the other failure modes can dominate the fire behaviour as well. As a result, design codes might overestimate the actual performance of fire exposed HC slabs. However, the experiments might represent a worst case compared to the practice. At least, fatalities caused by a premature collapse of fire exposed HC slabs, have never been reported up to the author's knowledge. Because there is a lack of fundamental understanding of the shear and anchorage behaviour, an optimum design between safety and economics can yet not be achieved. The objective of the research presented in this thesis is to gain a basic understanding of the shear and anchorage behaviour of fire exposed HC slabs and to develop FE models to predict this behaviour. With the models, design measures to improve the behaviour can be evaluated. The field of application is limited to HC slabs in accordance with the European product standard prEN 1168 [1197], exposed to standard fire conditions and simply supported on rigid supports like walls. The results are on the safe side for HC slabs with restraining support conditions.