Structural behaviors of strengthened deficient steel square hollow section columns under axial compressive loads

Engineers have often encountered many structural problems such as buckling, corrosion, and excessive loading and bending in damaged structures. To this end, the use of carbon-fibre reinforced polymer (CFRP) composites has expanded rapidly in recent years. These materials have many advantages over steel plates most important of which is their high strength-to-weight ratio. This article investigates the possible effects of CFRP and steel plates on retrofitting deficient steel square hollow section (SHS) columns. The effects of axial loading, stiffness, axial displacement, the position of the deficient region on the bottom of steel SHS columns, and slenderness ratio are examined through a detailed parametric study. Eight specimens are tested for failure under axial compression in a laboratory and simulated using finite element analysis based on a numerical approach. The results indicate a stress reduction in the damaged region caused by the application of CFRP sheets and steel plates which prevents or retards local deformation around the deficiency. Also, a deficiency can lead to the reduced load-carrying capacity of steel SHS columns, so the retrofitting method causes an increase in the steel columns' load-bearing capacity. Finally, CFRP performed better than steel plates in compensating axial force made by cross-section reduction due to the problems of using steel plates, such as in welding, increased weight, thermal stress around welding location, and the possibility of creating another deficiency by welding.