Performance of Concrete Panels Reinforced with Carbon Fiber–Reinforced Polymer Materials

As traffic loads increase and bridge infrastructure ages, it is becoming increasingly necessary to strengthen existing bridge members. Externally applied carbon fiber–reinforced polymer (CFRP) materials are often used to strengthen reinforced concrete structures. Four full-scale I-girder tests showed differences in the shear-strength contributions of anchored CFRP strips when they are applied in unidirectional U-wrap applications as opposed to bidirectional applications. Because the number of tests was so limited, a series of panel tests was developed to attempt to explain the role of unidirectional and bidirectional CFRP layouts. Concrete panels were constructed and tested under compressive forces generating bottle-shaped compression struts to evaluate effectiveness of CFRP strengthening. Although the results cannot be directly compared with the conditions in the web of an I-girder, they allowed consideration of a number of parameters that could not have been studied by using expensive full-scale I-girders. The effects of the inclination of CFRP strips relative to the direction of cracking, the layout of CFRP strips, and the amount of CFRP strip and anchor were studied through the panel tests. To prevent premature debonding of CFRP strips from the panel surface, CFRP anchors were used. The tests highlighted the most critical parameters that influence the effectiveness of CFRP materials in strengthening applications, especially for bidirectional CFRP layouts. Qualitative comparisons were presented on the basis of the panel tests. Bidirectional CFRP layout showed better crack control and strength gain than unidirectionally strengthened panels before unexpected CFRP anchor failure.