Strengthening Dapped Ends of Precast Double Tees with Externally Bonded FRP Reinforcement

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Abstract
A 90,000 square meter, three-story, precast concrete parking garage in Pittsburgh, PA was strengthened in order to address concerns regarding distress in the double tee beams supporting each elevated floor. Initially, the distress was manifest in inclined cracks forming at the reentrant corner of the dapped ends. During an independent load test of sample tees, additional cracks at approximately 1.5 m from the dapped end formed and became so severe that, at roughly 75% of the design load, the tees were deemed to have failed. This failure condition resulted in an effort to strengthen the ends of the tees in the garage for shear and flexure. In assessing various strengthening alternatives, externally bonded carbon fiber reinforced polymer (FRP) reinforcement was determined to be the most cost effective, the least disruptive to the operation of the parking garage, and virtually unnoticeable once the installation was complete. A load test of several tees after the installation of the FRP reinforcement demonstrated that the retrofitted tees could support loads over 100% of the design load. This paper presents the details of the design, specification, installation, and testing of the FRP strengthening system for this large retrofit project.

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