The Grand-Mere Bridge in the province of Quebec, Canada, is a 285 m (935 ft) long, cast-in-place, segmental box girder bridge that experienced several problems which resulted in distress characterized by an increasing deflection combined with localized cracking. These defects were due mainly to insufficient prestressing causing high tensile stresses in the deck and possible corrosion of the prestressing steel. To remedy this situation, the Quebec Ministry of Transportation strengthened the bridge by adding external prestressing equivalent to 30 percent of the remaining internal prestressing. The paper describes the causes of the distress and focuses on the assumptions adopted in the analyses to determine the current state of the bridge. The technique and design criteria used in strengthening the Grand-Mere Bridge are described. Also, the construction aspects and the various problems met during the external prestressing operation are discussed. The new technology and experience gained in strengthening this structure can be applied to both pretensioned and post-tensioned concrete bridges.
