Near-Surface Mounted, Fiber-Reinforced Polymer Strips for Negative-Moment Strengthening of Concrete Bridges—Design Methodology
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A bridge near Letohatchee, Alabama, was found to be deficient for certain types of truck loadings. Fiber-reinforced polymer (FRP) strips were selected to use in the strengthening scheme. Various models and code recommendations were studied and compared against existing experimental results to determine the most effective models for FRP-strengthened members. The models were divided into three groups: plate-end (PE) debonding models for near-surface mounted (NSM) FRP, intermediate-crack (IC) debonding models for externally-bonded (EB) FRP, and IC-debonding models for NSM FRP. None of the three PE-debonding models correlated well with the experimental results. Four of the six IC-debonding models for EB were relatively accurate for the test data. All five of the IC-debonding models for NSM produced mostly conservative results, with three models being relatively accurate. These three models—ACI 440 (2008), Standards Australia (2008), and Seracino et al. (2007a)—were used in the proposed strengthening scheme to determine the amount of NSM FRP the Letohatchee bridge needed. To verify this proposed design and to further examine the behavior of NSM-strengthened concrete members, a laboratory testing program was proposed. One of the main reasons for a laboratory testing program is that the published experimental test configurations do not match the Letohatchee bridge very well. The reinforcement ratios for the actual bridge are lower than the tests, and the NSM test specimens were not cracked prior to FRP strengthening. In the proposed testing program, the effects of the amounts of FRP and steel, the concrete compressive strength, and the cross-sectional shape were analyzed.