Gänstor Bridge, Ulm, Germany

The frame legs of this two-hinged bridge were formed by vertical columns and inclined prestressed ties. After 30 years of service, cracks in the superstructure occurred. Surveying revealed some ungrouted ducts with corrosion of prestressing steel. Besides repair measures (vacuum grouting, injection of cracks, restoration of concrete surface and water proofing) three strengthening options were considered:

• strengthening by means of external tension ties, i.e. permanent ground anchors
• strengthening with additional reinforced concrete and prestressed concrete elements
• strengthening of the superstructure by applying external tendons.

After analysis of cost and efficiency of each variant and their aesthetic aspects, the variant with permanent ground anchors was chosen.