Flexural Behavior of CFST Beams Partially Strengthened with Unidirectional CFRP Sheets: Experimental and Theoretical Study

The performance of simply supported concrete-filled steel tube (CFST) beams strengthened with unidirectional carbon fiber-reinforced polymer (CFRP) sheets was investigated. Twelve circular and rectangular beams were tested under flexure. Different CFRP strengthening configurations were investigated. In addition, a nonlinear finite-element (FE) analysis was performed to investigate the influence of different design parameters. The results show that the CFRP sheets significantly improved the moment capacity, flexural stiffness, and energy absorption (EA) capacity of the CFST beams. For example, the moment capacity and the EA capacity of circular beams increased by up to 38 and 18%, respectively, depending on the strengthening configuration. The strengthening scheme consisting of CFRP sheets applied on two sides for 75% of the beam length resulted in a similar strength enhancement compared with CFRP sheets applied along the entire beam length. Based on the results of the FE analysis, an empirical method was developed to predict the moment capacity of the CFST beams that were strengthened with CFRP sheets.