Concrete slabs with void formers are widely used in Europe, and through the application in a flat slab concept (biaxial bearing capacity) the shear and torsion resistance becomes important. With the knowledge of some critical tests for hollow core slabs there is a real need for a good understanding of the phenomena which can determine the shear capacity of such slabs. At the Warrington fire test laboratory of Ghent (Belgium) a test of such a system called Airdeck was executed several years ago. By the aid of comparison between EC2-1-2 design rules, thermo-plastic calculations and the reported phenomena we propose a design rule based on the test results.status: publishe