54-Year-Old Prestressed Concrete Bridge Beams Repaired with Mechanically Fastened FRP: Performance 2 Years after Repair

Abstract

A prestressed mechanically fastened retrofit system, which makes extensive use of strong, lightweight, and corrosion-resistant pultruded fiber-reinforced polymer (FRP) plates, was previously developed to provide a rapid, cost-effective means of extending the service life of deteriorated prestressed concrete bridges. The retrofit system was installed on three in-service prestressed concrete C-channel bridges in North Carolina, each over 50 years old at the time of the retrofit, and each of which remained in service for approximately 2 years while replacement projects were planned and scheduled. Following demolition of two of these bridges, five retrofitted beams and seven companion control beams were retrieved for this research program. The research program included full-scale static and cyclic fatigue loading of beams in flexure to evaluate the condition and performance of beams after 56 years of service with the retrofits applied for the last two of those years, including environmental exposure and traffic loading. Results showed that installing the mechanical retrofit system on both stems of a prestressed concrete channel member increased member capacity beyond the original design levels, exceeding the ultimate capacity of the unstrengthened beams by an average of 24% and decreasing midspan deflections at failure by an average of 18%. In addition, all strengthened stems and many unstrengthened stems performed well in fatigue, with the strengthened members achieving on average 81% more cycles prior to the conclusion of fatigue testing than unstrengthened members. All observed fatigue failures in strengthened specimens were controlled by the concrete rather than in the retrofit components, indicating good durability of the retrofit system. Based on these findings, the recommended service life of the retrofit system can be extended to a maximum of 5 years, provided inspections of the system and the underlying concrete girders are conducted regularly.