Service and Ultimate Behaviour of Slim Floor Beams: An Experimental Study

Slim floor systems represent an economical and competitive solution for building applications that combine the advantages of concrete floors, prefabricated steel sections and a shallow depth. The distinctive feature of this form of construction relies on the fact that the lower steel flange is wider than the top flange to provide a continuous support along the beam length for the slab formwork. The latter is usually specified in the form of either profiled sheeting or cellular slabs. In this structural typology, the steel section is embedded within the thickness of the slab. This paper presents an experimental study aimed at evaluating the service behaviour of slim floor beams induced by the time-dependent behaviour of the concrete and at establishing the possible influence of creep effects on their ultimate response. For this purpose, two slim floor samples were prepared in a simply-supported configuration. Their long-term deflections and deformations were monitored over time for about ten months, after which the specimens were tested to failure. The specimens possessed identical concrete and steel geometries. The shear connection was provided by transverse steel reinforcing bars installed within regularly spaced holes incorporated in the steel web. The samples were cast unpropped so that the self-weight of the wet concrete was carried by the steel member. The only difference between the two specimens consisted in the loading history specified over time. In particular, one slim floor sample was kept unloaded for the entire duration of the test to monitor the influence of shrinkage effects while the second specimen was subjected to a sustained load to evaluate the effects of both creep and shrinkage. The experimental data reported in this study provides insight into their long-term and ultimate response, and valuable benchmarking data for the calibration of numerical models and design procedures related to the serviceability and ultimate limit states of slim floor systems.