Post-Tensioned Concrete Beams Strengthened in Shear Using Fiber-Reinforced Polymer Laminates and Patch Anchors

Abstract

Strengthening concrete bridges using fiber-reinforced polymers (FRPs) in flexure, shear, and torsion is limited by the occurrence of premature FRP debonding which often controls the degree of strengthening possible using this approach. To address this issue, anchorage systems have been developed in recent years to mitigate FRP debonding failure modes with the objective of achieving higher levels of strengthening using less material. Of the many types of anchorage systems researched to date, joint level tests have revealed that bidirectional fiber patches placed at the ends of the FRP laminates can significantly delay the occurrence of FRP debonding. This study presents the first experimental application where patch anchors are evaluated in post-tensioned concrete beams strengthened in shear using FRP laminates. Three specimens were tested including an unstrengthened control beam and strengthened beams with and without anchors. The anchors were proven to significantly improve the shear capacity of the member and increase the FRP laminate strain utilization prior to failure. The experimental results were verified against predictions provided by the modified compression field theory (MCFT) and the ACI 318. A semiempirical model (SE model) was proposed to predict the shear contributions provided by the anchored FRP laminates.