Abstract This paper deals with the experimental analysis of the mechanical behaviour of bonded steel–concrete composite structures. The steel girder and the concrete slab are assembled by adhesives. The effect of the main parameters, such as the adhesive nature and the irregular thickness of the adhesive joint, on mechanical performance and ultimate load is studied. Two adhesives are used in this work. The results show that the connection between the steel girder and the concrete slab ensured by epoxy adhesive is perfect and without any slip in the steel–concrete interface. In the case of the composite beam interface ensured by polyurethane, the connection is flexible. The influence of the variation in adhesive thickness, 2 mm in the transverse direction and 4 mm in the longitudinal direction, on the mechanical behaviour and ultimate force is not important. The first cracks in the concrete slab appear in the transverse direction. The experimental results show that it is possible to realise a steel concrete composite structure bonded by adhesive.