This paper presents the effect of prestress levels in prestressed, carbon-fiber-reinforced-polymer (CFRP) laminates for strengthening prestressed concrete beams based on a validated, nonlinear, three-dimensional finite-element-analysis model. A total of nine medium-scale prestressed concrete beams, six of which were externally strengthened with prestressed CFRP laminates, were studied to examine the contribution of various prestressing levels in the CFRP laminates to flexural behavior of the strengthened beams. The focus of this study was on the load-deflection responses, strain development in the internal and external reinforcement, elastic and plastic energycharacteristics, and failure predictions. For a practical use of this type of strengthening method, the recommended level of prestress is between 20% and 30% of the ultimate design strain of the CFRP laminates. More research, however, may be warranted to draw a general design guideline for the prestress level, including various size effects and reinforcement ratios of prestressed concrete beams.
