Proposing a Relationship for Calculating the Strength of Confined Concrete for Bridge RC Columns Strengthened with FRP

Bridges are unique in their structural response compared to buildings. As the bridgesare considered as vital lifelines in transportation, providing sufficient seismicsecurity is very important. However, bridges have a lower degree of staticindeterminacy than buildings; Hence, failure of a part of structural element such as acolumn or a foundation likely results in a collapse of the entire bridge system. Duringan earthquake, a RC column can fail in three main modes due to cyclic axial andlateral loads: shear failure, flexural plastic hinge failure, and lap splice failure. Inrecent years, Use of FRP composites as one of the strengthening techniques forreinforced concrete bridges, has been increasingly developed. The Fiber ReinforcedPolymer (FRP) strengthening procedure would cause minimal increase in size andweight of structural members, ease of installation and efficient corrosion resistance.In this paper a compressive strength model for confined concrete wrapped with fiberreinforced polymer has been proposed which is an extension of Mohr’s strengththeory. This model relates the confined compressive stress to the confining pressure.In the general form this model requires information about the uni-axial compressivestrength, the uni-axial tensile strength and a quantity, n, relating to the shape ofMohr’s envelope of ultimate strength states. A second-order parabolic model,developed analytically, is proposed for using with FRP-confined concrete. Theproposed model has been verified using existing tests of normal strength concretespecimens confined by FRP wrap. An application example for strengthening areinforced concrete bridge column is also provided.