The aim of this test study was to achieve an in-situ strengthening technique to retrofit the deteriorated tall steel structures using carbon fiber-reinforced polymer (CFRP). A total of 20 structural steel channel sections with various retrofitting configurations were tested to arrive at an optimal strengthening technique to improve the buckling mode of failure of structural steel channel section under flexural loading. An approach of transforming the open cross section to closed cross section was used to increase the torsional resistance of channel sections. The various parameters such as type of CFRP fabric, wrapping configuration (skin and closed wrap) and number of CFRP layers were also included in this study. The results indicate that the closed wrapped configuration with an additional (final) layer of bi-directional CFRP fabric provides the higher strength and stiffness compared to control and skin wrapped specimen due to the confinement of hoop directional fibers. This study also proves that the lateral torsional buckling (LTB) mode of failure of open cross section specimens can be improved by appropriate CFRP strengthening techniques. © 2016 Elsevier Ltd