Use of Fiber Reinforced Polymer Composites for Repair or Retrofit of Prestressed Box Girders

Viable retrofit schemes are necessary to delay or offset replacement of deteriorating concrete bridge members. Carbon fiber reinforced polymer (CFRP) pultruded plates can be especially effective when retrofitting bridge members where stiffness, fatigue resistance, ease of installation, and weathering characteristics are a concern. The research reported in Chapter 1 was undertaken to examine the influence of fatigue loading, prior cracking, and patch materials on flexural performance of reinforced concrete members retrofitted with externally bonded CFRP plates. Moreover, experimental data from the six reinforced concrete beams tested as part of this research are expected to further evaluate available design equations for external retrofitting of reinforced concrete structures. The test results do not suggest a significant effect of fatigue loads; show that existing cracks do not significantly impact the strength of retrofitted members; and indicate that patch materials can reduce the available bond strength, and require additional surface preparation. The research reported in Chapter 2 presents a novel design approach utilizing externally bonded CFRP plates developed in an attempt to overcome construction errors in a member removed from an adjacent box girder bridge. The design methodology was evaluated based on data from testing of a retrofitted girder along with previous tests on as-is girders. Test data suggest appreciable improvements in terms of load carrying capacity and stiffness of the retrofitted girder. The relatively simple retrofit plan developed could have been used to delay replacement of the deficient girders. The research reported in Chapter 3 is aimed at filling some of the gaps in the available test data through retrofitting and testing of a 18.3 m (60 ft) prestressed box girder retrofitted with CFRP composite plates with mechanical anchors. Prior research on the use of CFRPs for retrofitting of existing structures has predominantly focused on mildly reinforced concrete members, and application to prestressed members is rather limited. Moreover, data regarding performance of mechanical anchors for enhancing bond characteristics of CFRP composites are scant. After a description of the design procedure, the test data are used to evaluate the design method, current design recommendations, and performance of mechanical anchors.