Lightweight steel concrete structures (LSCS) - an innovative building structure type that can be used both as load-bearing and as enclosing one. They consist of profiled steel - usually galvanized and cold-bent - filled with a monolithic foam concrete with a 400…1200 kg/m3 density, and with fiber cement sheets sheathing. In view of the current Standarts, codes and scientific literature there is no methodology for foam filling when calculating the strength of such structures, the goal is to determine the condition load effect factor of profile steel in LSCS. In this paper, based on experimental data, a comparison of two types of floor slabs is considered: LSCS fabricated of foam concrete with a density of 400 kg/m3 and similar slabs made of profile steel elements, fiber-cement sheets without filling with monolithic foam concrete. Three samples of panels of each type were loaded with uniformly distributed load, which gradually increased from zero to failure values using three jacks, each of which transmitted the load to the slab at two points. It has been experimentally proved that the foam concrete, despite its own extremely low strength class, actually includes in the operation, preventing such effects as stability local loss, crushing and profile steel elements cross-section warping and increases the slabs overall load capacity by 20-25%., which corresponds to a condition load effect factor of at least 1.2…1.25.