Long-Term Multipliers and Deformability of Fiber-Reinforced Polymer Prestressed Concrete

This paper presents the flexural characteristics of highway bridge girders prestressed with fiber-reinforced polymer (FRP) tendons. Of interest are the technical challenges identified by ACI Subcommittee 440-I (FRP-Prestressed Concrete): long-term multipliers, deformability, and minimum reinforcement. Aramid and carbon FRP (AFRP and CFRP, respectively) composites are used to prestress concrete girders. Based on analytical models, new design expressions are proposed for the aforementioned items, followed by an assessment using laboratory test data and full-scale benchmark bridges. The long-term multipliers calibrated per reliability theory are mostly different from the empirical multipliers adopted in ACI 440.4R-04. The girders prestressed with AFRP/CFRP sufficiently deform in flexure, even though their moment-curvature responses are not comparable with those of steel-prestressed girders. The new deformability index specifies design requirements for AFRP/CFRP-prestressed members with either compression-controlled or tensioned-controlled sections. The importance of a potential change in FRP modulus during the service life of prestressed concrete girders is examined. A factored ultimate-to-cracking moment ratio of phi M-n/M-cr = 1.2 is suggested for girders prestressed with AFRP/CFRP, which aligns with the articles of existing design manuals and specifications dedicated to prestressed concrete.