Test of prestressed concrete T-beams retrofitted for shear and flexure using carbon fiber reinforced polymers

Abstract

In 1997, a precast prestressed T-Beam in the Ala Moana Shopping Center Parking Garage was strengthened in flexure using carbon fiber reinforced polymer (CFRP). When the old parking garage was demolished in June 2000 to make way for a new multilevel parking garage, this beam and two control beams were salvaged and transported to the University of Hawaii at Manoa Structural Testing Laboratory for testing. This thesis presents testing of the strengthened beam and a control beam. It also describes the retrofit procedures during field application of the CFRP strips, beam recovery, and preparation for laboratory testing. In addition, a step by step analysis of the predicted strengths is presented. To ensure flexure failure, the beams were retrofitted in shear with CFRP. Two types of wrapping schemes were used and anchorage was provided for the shear retrofit. The left half of each beam was retrofitted with 3" wide double layer CFRP stirrups. The right half of each beam was retrofitted with 12" wide CFRP sheets. After flexural testing, each half of each beam was recovered for shear testing. Flexural test results indicate that the CFRP strengthening provided a 71% increase compared with the control specimen without reducing the beam's ductility. The flexural capacity of the strengthened beam was 21% greater than predicted by ACI 440R-02. The failure shear strength of the beams with CFRP sheets was slightly greater than the ACI 440R-02 prediction. The shear tests indicated delamination of the CFRP stirrups and sheets occurring prior to the maximum shear load. Anchorage at the top and bottom of the beam web helped prevent complete delamination of the CFRP; however further anchorage development is required to maximize the strength of the CFRP shear retrofit.