Structural Assessment of AASHTO Type II Prestressed Concrete Girder with GFRP or Stainless-Steel Shear Reinforcement

Concrete bridges in extremely aggressive environments deteriorate mainly from corrosion of carbon steel prestressing strands and rebars. In prestressed concrete girders, corrosion might occur in the transverse reinforcement, which results in a decrease in shear resistance. Corrosion-free glass fiber reinforced polymer (GFRP) rebars and corrosion-resistant stainless steel rebars are promising solutions to address corrosion. However, GFRP rebars have lower ultimate strain, elastic modulus, and transverse shear capacity than stainless steel rebars. Two full-scale 12.8-m (42-ft) long AASHTO (American Association of State Highway and Transportation Officials) Type II girders with a deck slab on top of them were tested in shear at both ends. One girder was reinforced with duplex stainless steel Grade 520 (75) stirrups, and the other was reinforced with GFRP stirrups. Both girders had 11 carbon steel prestressing strands, each initially stressed to 75% of the strand's ultimate stress. The girders were composite with a deck slab and had a smooth interface between the girder and slab. The objective was to experimentally assess the structural behavior of the girders. The girder reinforced with stainless steel stirrups failed in flexural shear while the girder reinforced with GFRP stirrups failed in interface shear due to the lower transverse shear capacity of GFRP rebars and smooth interface between the girder and slab. The experimental shear force at the failure of the girder reinforced with stainless steel stirrups was 9.1% greater than that reinforced with GFRP stirrups. Also, the direct replacement of stainless steel confinement reinforcement with GFRP resulted in strand slippage. It was found that the current AASHTO LRFD shear design provisions are conservative in predicting the vertical shear resistance of a girder reinforced with stainless steel stirrups or GFRP stirrups. The research findings will be helpful in the development of design guide specifications for prestressed concrete girders reinforced with GFRP stirrups.

Automated summary

Concrete bridges can deteriorate from corrosion of carbon steel prestressing strands and rebars. Using corrosion-resistant materials like GFRP and stainless steel can help address this issue, but they have differences in ultimate strain and shear capacity.