Lightweight steel-concrete structures (LSCS) are a type of steel-concrete structures where the filling concrete is monolithic (pouring) foam concrete with density 100-1000 kg/m3, the profile steel is lightweight steel thin-walled structures (LSTS), and fiber cement panels perform the function of non-removable formwork. As a rule, these structures are made of structural and heat-insulating foam concrete, which has good insulation and technical characteristics and sufficient strength. The object of the study is lightweight steel-concrete slab panels, which are one of the special cases of LSCS, made of monolithic foam concrete with density of 400 kg/m3. An analysis of the bending stiffness of LSBC slab panels by comparing the experimental data with analytical calculations was carried out. It was found that bendable LSCS made of monolithic foam concrete with density of 400 kg/m3 operate in physical nonlinear way. It was shown that the bending stiffness of LSCS floor panels can be determined as the sum of stiffnesses of profiled steel and foam concrete at the linear stage of work. The reliability of the proposed methodology within the limits of linear operation was demonstrated. It was proved both experimentally and theoretically that the bending stiffness of panels based on LSCS is higher than the bending stiffness of similar panels made of lightweight thin-walled steel (LTSS) by about 30%.