Experimental behaviour of concrete floor slabs at large displacements

This paper presents the results from 15 small-scale tests conducted on horizontally unrestrained slabs which were subjected to large vertical displacements. All the tested slabs showed a load-carrying capacity far greater than the design capacity using the well-established yield-line theory. The purpose of these tests was to investigate the influence of isotropic and orthotropic reinforcement, together with reinforcement bond strength, on the degree of mobilisation of tensile membrane action, and thus on the load capacity of the slab. The results of the tests have been compared to a previously developed design method which incorporates membrane action of composite floor slabs into the estimation of their load capacity in fire, where large vertical displacements are acceptable provided that compartmentation is maintained. This comparison shows that the design method compares well with experimental results and is generally conservative, although it is in need of development to account for the bond characteristics of reinforcement and changes of failure mode for some orthotropically reinforced slabs.