Improving the Mechanical Resistance of a Slender RHS Steel Profile with Polymeric Insert

Rectangular hollow section (RHS) profiles gained leading positions in various structural applications mainly because of their aesthetic appearance and structural integrity, ensuring efficient utilization of steel. In addition, the lightweight of the profiles and high resistance to torsion simplify manufacturing and building processes. However, reducing the weight makes such elements susceptible to undesired premature buckling when a structure loses its stability at the loading well below the theoretical strength limit of the material. Despite years of design practice, the above problem limits the further decrease of the RHS thickness. This study considers an alternative approach employing a low-density polymeric insert to ensure the local load-bearing capacity of the RHS fragment. The results of the 100 mm long fragment of the slender RHS 200/100/4 (height/width/thickness) profile compressive tests provide the adequacy of the numerical (finite element) model used for assessing the mechanical efficiency of the proposed strengthening concept. The 3D printing technology offered the 10% density and precise geometry of the polymeric insert that increased the weight of the RHS fragment by only 28%. At the same time, the mechanical resistance of the hybrid cross-section increased two times regarding the reference (non-strengthened) RHS sample. This effect corresponds to the profile thickness increase from 4 mm to 6 mm, i.e., 1.5 times increasing the profile weight. The possibility of using recycled plastics for strengthening purposes increases the economic effect of the proposed concept.