Behavior of a Damaged Prestressed Concrete Bridge Repaired with Fiber-Reinforced Polymer Reinforcement

Abstract

After the construction of elevated portions of I-565 in Huntsville, Alabama, cracks were discovered in numerous prestressed concrete bulb-tee bridge girders that were constructed to exhibit continuous behavior in response to post-construction loads. Previous investigations conducted by Alabama Department of Transportation (ALDOT) and Auburn University Highway Research Center (AUHRC) personnel resulted in determinations that the cracking was a result of restrained thermal deformations and inadequate reinforcement details, and that the cracking compromised the strength of the girder end regions. A wet lay-up fiber-reinforced polymer (FRP) repair scheme was proposed to address the deficiency. To assess the efficacy of the FRP repair solution, load testing and finite element model (FEM) analyses were conducted for pre- and post-repair conditions of Northbound Spans 10 and 11. Pre-repair testing was conducted on June 1 and 2, 2005. The FRP reinforcement system was installed in December 2007. Post-repair testing was conducted on May 25 and 26, 2010. ;Post-repair testing included controlled truck loading as well as the monitoring of structural response to diurnal thermal conditions. Analysis of pre- and post-repair results indicated that the efficacy of the repair solution could not be assessed with direct comparisons between pre- and post-repair measurements due to unforeseen unintentional support conditions that were in effect during the pre-repair testing. Direct analysis of post-repair behavior indicated that the structure exhibits continuity degradation in response to heavy truck loads and should be considered simply supported for conservative strength-limit-state design. Analysis of responses to thermal conditions indicated the FRP reinforcement exhibits behavior that can be accurately estimated with simplified analysis of linear temperature gradient effects on restrained girders. Based on conditions observed after more than 2 years in service, the installed FRP reinforcement system was determined to be performing appropriately. ;Based on the experimental observations, a design procedure was developed for FRP repair of similar structures with damaged regions near continuous ends of prestressed concrete bridge girders in accordance with AASHTO LRFD Bridge Design Specifications and the recommendations of ACI 440.2R-08. The design procedure was formulated to provide the girder end regions with adequate strength-limit-state resistance for the combined effects of shear and flexure, as well as to provide adequate performance under service loads—including the effects of daily temperature variations. A design example is presented.