The accurate modelling of composite slabs through finite elements (FE) can describe the complex phenomena occurring between the steel and concrete materials. Current semi-empirical design methods based on full scale test require an expensive process to characterize the composite slab performance and provide limited insights on the actual materials comportment. This paper presents early results on an accurate geometrical and physical 3D FE modelling of a full scale bending tests with the potential to describe both materials’ macro and micro behaviours. With a focus on the modelling of the concrete elements, this study leverages experimental tests to assess robustness of some variables at the FE models, recommending a novel approach for accurate modelling.