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

Bridges are unique in their structural response compared to buildings. As the bridges are considered as vital lifelines in transportation, providing sufficient seismic security is very important. However, bridges have a lower degree of static indeterminacy than buildings; Hence, failure of a part of structural element such as a column or a foundation likely results in a collapse of the entire bridge system. During an earthquake, a RC column can fail in three main modes due to cyclic axial and lateral loads: shear failure, flexural plastic hinge failure, and lap splice failure. In recent years, Use of FRP composites as one of the strengthening techniques for reinforced concrete bridges, has been increasingly developed. The Fiber Reinforced Polymer (FRP) strengthening procedure would cause minimal increase in size and weight 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 strength theory. This model relates the confined compressive stress to the confining pressure. In the general form this model requires information about the uni-axial compressive strength, the uni-axial tensile strength and a quantity, n, relating to the shape of Mohr’s envelope of ultimate strength states. A second-order parabolic model, developed analytically, is proposed for using with FRP-confined concrete. The proposed model has been verified using existing tests of normal strength concrete specimens confined by FRP wrap. An application example for strengthening a reinforced concrete bridge column is also provided.