Behavior of full-scale reinforced concrete beams retrofitted for shear andflexural with FRP laminates

Four full-scale reinforced concrete beams were replicated from an existing bridge. The original beams were substantially deficient in shear strength, particularly for projected increase of traffic loads. Of the four replicate beams, one served as a control and the remaining three were implemented wi th varying configurations of carbon fiber reinforced polymers (CFRP) and gl ass FRP (GFRP) composites to simulate the retrofit of the existing structur e. CFRP unidirectional sheets were placed to increase flexural capacity and GFRP unidirectional sheets were utilized to mitigate shear failure. Four-p oint bending tests were conducted. Load, deflection and strain data were co llected. Fiber optic gauges were utilized in high flexural and shear region s and conventional resistive gauges were placed in eighteen locations to pr ovide behavioral understanding of the composite material strengthening. Fib er optic readings were compared to conventional gauges. Results from this study show that the use of fiber reinforced polymers (FRP ) composites for structural strengthening provides significant static capac ity increases approximately 150% when compared to unstrengthened sections. Load at first crack and post cracking stiffness of all beams was increased primarily due to flexural CFRP. Test results suggest that beams retrofit wi th both the designed GFRP and CFRP should well exceed the static demand of 658 kN m sustaining up to 868 kN m applied moment. The addition of GFRP alo ne for shear was sufficient to offset the lack of steel stirrups and allow conventional RC beam failure by yielding of the tension steel. This allowed ultimate deflections to be 200% higher than the pre-existing shear deficie nt beam. If bridge beams were retrofit with only the designed CFRP failure would still result from diagonal tension cracks, albeit at a 31% greater lo ad. Beams retrofit with only the designed shear GFRP would fail in flexure at the mid-span at an equivalent 31% gain over the control specimen, failin g mechanism in this case being yielding of the tension steel. Successful mo nitoring of strain using fiber optics was achieved. However, careful planni ng tempered by engineering judgement is necessary as the location and gauge length of the fiber optic gauge will determine the usefulness of the colle cted data. (C) 2000 Elsevier Science Ltd. All rights reserved.