Fatigue Behavior of Concrete Bridge Decks Cast on GFRP Stay-in-Place Structural Forms and Static Performance of GFRP-Reinforced Deck Overhangs

Abstract

The first part of the thesis addresses the fatigue performance of concrete bridge decks with GFRP stay-in-place structural forms replacing the bottom layer of rebar. The forms were either flat plate with T-up ribs joined using lap splices, or corrugated forms joined through pin-and-eye connections. The decks were supported by simulated Type III precast AASHTO girders spaced at 1775mm (6ft.). Two surface preparations were examined for each GFRP form, either using adhesive coating that bonds to freshly cast concrete, or simply cleaning the surface before casting. For the bonded deck with flat-ribbed forms, adhesive bond and mechanical fasteners were used at the lap splice, whereas the lap splice of the unbonded deck had no adhesive or fasteners. All the decks survived 3M cycles at 123kN service load of CL625 CHBDC design truck. The bonded flat-ribbed-form deck survived an additional 2M cycles at a higher load simulating a larger girder spacing of 8ft. Stiffness degradations were 9-33% with more reduction in the unbonded specimens. Nonetheless, live load deflections of all specimens remained below span/1600. The residual ultimate strengths after fatigue were reduced by 5% and 27% for the flat-ribbed and corrugated forms, respectively, but remained 7 and 3 times higher than service load. The second part of the thesis investigates the performance of bridge deck overhangs reinforced by GFRP rebar. Overhangs of full composite slab-on-girder bridge decks at 1:2.75 scale were tested monotonically under an AASHTO tire pad. Five tests were conducted on overhangs of two lengths: 260mm and 516mm, representing scaled overhangs of 6ft. and 8ft. girder spacing, respectively. The 260mm overhang was completely reinforced with GFRP rebar while the 516mm overhang consisted of a GFRP-reinforced section and a steel-reinforced section. The peak loads were approximately 2 to 3 times the established equivalent service load of 24.3kN, even though the overhangs were not designed for flexure according to the CHBDC but rather with lighter minimum reinforcement in anticipation of shear failure. The failure mode of each overhang section was punching shear. The steel-reinforced overhang section exhibited a greater peak load capacity (13.5%) and greater deformability (35%) when compared to the GFRP-reinforced overhang section.