Abstract: A duct for enclosing post tension reinforcing tendons includes a first closed circumference conduit having at least one minimum internal radius. The conduit includes at least one corrugation including two longitudinally spaced apart end members wherein a radial outer surface of each end member defining at least one external radius. A reduced diameter portion is disposed between the two end members. The reduced diameter portion defining at least one intermediate radius larger than the at least one minimum internal radius and smaller than the at least one external radius.

Abstract: A method for reinforcing a structure involves winding a cable around the structure and tensioning the cable after the ends of the cable are secured. Winding the cable around the structure involves winding a portion of the cable near the top end of the structure such that at least two windings of the cable are made with a first predetermined separation between the windings, and winding another portion of the cable near the bottom end of the structure such that at least two bottom windings of the cable are made with a second predetermined separation between the bottom windings. In one embodiment, the structure is a concrete column. In another embodiment, tensioning the cable involves installing a plurality of shims between the cable and the structure at spaced locations along the cable. A structure which is reinforced using such a method is also described.