Keywords: carbon fiber reinforced polymer, collision, damaged, girder, research, repair, efficiency.

With the evolution of carbon fibre reinforced polymer (CFRP) as a new technology for strengthening or repairing structural components efforts have been made to quantify its applied behaviour in order to develop standard codes for the use of the material. The current American reference for designing externally bonded CFRP applications is the ACI 440.2R-08. However, the document is forthright about its short comings and refers to durability and debonding behaviour as "areas that still require research" [1]. It continues to state specifically that "more accurate methods of predicting debonding are still needed" [1]. It was these limitations in the current reference, lack of independent research documented on strengthening beams with pre-existing damage, and the frequency of overheight collisions that invoked this research.

In this study a total of thirty-four reinforced concrete (RC) beams and nine prestressed concrete (PSC) girders were tested in flexure until failure. The study was designed to include investigations into the effects of the reinforcement ratio, the cross-section, the CFRP configuration, and the level of strengthening on the performance of CFRP repair methods.

Two sets of designs for the RC specimens were used; both were 8.0 ft long with cross-section dimension of 5.5 inches by 10.0 inches. However, one set contained 3 #4 reinforcing bars and the other contained 3 #3 reinforcing bars. The simulated damage was implemented by cutting and bending one of the reinforcing bars prior to casting. The nine PSC specimen tested for this research had cross-sectional dimensions exactly half the scale of an AASHTO type II girder. An additional decking 4 inch thick was also cast on top of the beams to simulate a bridge deck. A total of five seven-wire low relaxation prestressing strands were used in each beam along with three non-prestressed reinforcements in the girder and two more in the topping. All test specimens were loaded under a four point loading setup at a static rate until failure. Multiple measurements of strains, deflections, and applied loads were collected and recorded during the testing of all beams and girders.

From the research performed the following conclusions were made:

1. CFRP repairs can result in a wide range of flexural capacity increases ranging from 22% to 353% compared with a control damaged beam, depending on the reinforcement ratio, CFRP layers, and U-wrapping configuration.
2. Intermediate anchoring U-wrappings can help to mitigate debonding by suppressing the strain of the longitudinal CFRP laminate.
3. Providing a spacing between U-wrappings can be a successful repair alternative when compared to a fully wrapped section with no spacing between U-wrappings.
4. Further analysis of testing data is needed to make concrete conclusions as to which CFRP configuration is optimal for various cross-section sizes, shapes, and levels of strengthening.

1

ACI Committee 440, "Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures", ACI 440.2R-08, American Concrete Institute, Farmington Hills MI, USA, 2008.

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