Ian N. Robertson and Alison
Agapay
Department of Civil and Environmental Engineering, University of Hawaii at Manoa, 2540 Dole St. Holmes Hall 383, Honolulu, HI 96822
Carbon Fiber Reinforced Polymers has become a valuable material for repairing and retrofitting damaged or deficient structures. Numerous research studies have shown that carbon fiber reinforced polymer sheets or strips bonded to the concrete surface can substantially increase flexural, shear and compressive strength of concrete members.
In 1997, a precast prestressed T-Beam in the Ala Moana Shopping Center Parking Garage was strengthened in flexure using carbon fiber reinforced polymer. 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 report presents testing of the strengthened beam and a control beam. It also describes the retrofit procedures during field application of the carbon fiber reinforced polymer 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 carbon fiber reinforced polymer. Two types of wrapping scheme were used and anchorage was provided for the shear retrofit. The left half of each beam was retrofitted with 3” wide double layer carbon fiber reinforced polymer stirrups. The right half of each beam was retrofitted with 12” wide carbon fiber reinforced polymer sheets. After flexural testing, each half of each beam was recovered for shear testing.
Flexural test results indicate that the carbon fiber reinforced polymer 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 two T-Beam tests with carbon fiber reinforced polymer sheets for shear strengthening produced 7% and 16% increases in the shear capacity when compared with the control beam without carbon fiber reinforced polymer shear strengthening. These increases are below the 42% increase predicted by ACI 440R-02. Because of conservatism in the estimate of concrete and internal steel stirrup contribution to the shear capacity, the failure shear strength of the beams with carbon fiber reinforced polymer sheets was still slightly greater than the ACI 440R-02 prediction for ultimate shear capacity. The shear tests indicated delamination of the carbon fiber reinforced polymer 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 carbon fiber reinforced polymer; however further anchorage development is required to improve the strength of the carbon fiber reinforced polymer shear retrofit.
Department of Civil and Environmental Engineering, University of Hawaii at Manoa, 2540 Dole St. Holmes Hall 383, Honolulu, HI 96822
Carbon Fiber Reinforced Polymers has become a valuable material for repairing and retrofitting damaged or deficient structures. Numerous research studies have shown that carbon fiber reinforced polymer sheets or strips bonded to the concrete surface can substantially increase flexural, shear and compressive strength of concrete members.
In 1997, a precast prestressed T-Beam in the Ala Moana Shopping Center Parking Garage was strengthened in flexure using carbon fiber reinforced polymer. 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 report presents testing of the strengthened beam and a control beam. It also describes the retrofit procedures during field application of the carbon fiber reinforced polymer 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 carbon fiber reinforced polymer. Two types of wrapping scheme were used and anchorage was provided for the shear retrofit. The left half of each beam was retrofitted with 3” wide double layer carbon fiber reinforced polymer stirrups. The right half of each beam was retrofitted with 12” wide carbon fiber reinforced polymer sheets. After flexural testing, each half of each beam was recovered for shear testing.
Flexural test results indicate that the carbon fiber reinforced polymer 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 two T-Beam tests with carbon fiber reinforced polymer sheets for shear strengthening produced 7% and 16% increases in the shear capacity when compared with the control beam without carbon fiber reinforced polymer shear strengthening. These increases are below the 42% increase predicted by ACI 440R-02. Because of conservatism in the estimate of concrete and internal steel stirrup contribution to the shear capacity, the failure shear strength of the beams with carbon fiber reinforced polymer sheets was still slightly greater than the ACI 440R-02 prediction for ultimate shear capacity. The shear tests indicated delamination of the carbon fiber reinforced polymer 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 carbon fiber reinforced polymer; however further anchorage development is required to improve the strength of the carbon fiber reinforced polymer shear retrofit.
No comments:
Post a Comment