The object of research is a reinforced concrete T-beam element of prefabricated monolithic slabs with a thin-walled steel profile. Previously, the steel profile was used in the beams as a stay-in-place formwork, while the authors proposed to include it in the structural behaviour by anchoring. Four variants of T-beam elements have been tested to assess the influence of a thin-walled steel profile on the load-bearing capacity over normal sections. As a result, the strength capacity of reinforced concrete beams with anchored steel profile is 55% higher than the strength capacity of similar samples without steel profile.