Prestressed CFRP Strips for Concrete Bridge Girder Retrofitting: Application and Static Loading Test

This paper presents an investigation on the practicability and structural efficiency of prestressed carbon-fiber–reinforced polymer (CFRP) strips with a gradient anchorage in the framework of a bridge-strengthening application in Poland. The nonmechanical anchorage system avoids the installation of metallic bolts and plates, with the exception of a temporary support frame. Two 18.4-m-long large-scale prestressed concrete girders were produced following the drawings of the existing bridge construction. One girder served as a reference, and the second one was strengthened with two prestressed CFRP strips. In this case, the initial negative cambering was leveled out by a layer of dry shotcrete. CFRP strips with a prestrain of 0.58% were applied for flexural upgrading. Both girders with a total length of 18.4 m were finally statically loaded up to failure to assess the strengthening efficiency in flexure of the retrofitting technique used. Tensile failure of the CFRP strips was reached, indicating an optimal use of the composite reinforcement. The strengthened girder exhibited a ductile behavior up to strip rupture with a distinct steel yielding and a subsequent pronounced increase of the load-carrying capacity. For service load considerations, an enhancement of the cracking load of approximately 16% was noticed. In terms of ultimate load, a significant improvement of approximately 25% compared to the reference girder was reached. Although some practical problems need optimization, the presented results are very promising and make this strengthening system an alternative for future retrofitting applications in bridge engineering.