Experimental Studies on Strength and Stiffness Enhancement in CFRP-Strengthened Structural Steel Channel Sections under Flexure

An experimental study to investigate the stiffness and strength enhancement in a structural steel channel section strengthened by six different carbon fiber-reinforced polymer (CFRP) wrapping configurations is described in this paper. An approach of transforming the singly symmetric open section such as a channel section to a closed section by CFRP wrapping as a means to increase the stiffness and strength is demonstrated. A total of 21 specimens, both CFRP reinforced and bare steel specimens, were tested in four-point bending. Two different CFRPs, unidirectional and bidirectional fabrics, were used in wrapping the specimen. While the unidirectional layers contribute to the stiffness and strength, the bidirectional layer primarily contributes to confining the former in addition to increasing the resistance to lateral torsional buckling (LTB) of the specimens. The results indicate that the CFRP-strengthened closed sections confined by bidirectional fabrics are effective in enhancing the strength and stiffness compared to CFRP skin-strengthened sections (perimeter of bare steel channel sections overlayed with CFRP). The effectiveness of the closed section can be further improved by increasing the unidirectional CFRP layers prior to the final wrapping by bidirectional fibers. The variation in stiffness for all the CFRP configurations from the initial loading of specimens up to the ultimate is also investigated. This paper demonstrates that the strength and stiffness of steel channel sections can be significantly enhanced by means of appropriate CFRP wrapping configuration.