Balthasar Novák

Present traffic loads on bridges often exceed the actions anticipated at the time of construction. In Germany several prestressed concrete bridges with deficits in their load bearing capacity had been identified. An established retrofitting method is the installation of external tendons with deviation and anchorage blocks. Since the later proved to be a critical detail, their structural behaviour was monitored for three bridges in Hessen. The anchorage blocks were fitted with extensometers, strain gauges were installed on prestressing rods and the temperature was recorded. Also alert protocols were established, to detect potentially hazardous situations. The effects of different construction stages were tracked. The influence of short- and long-term temperature changes on the readings was assessed. In summary, the monitoring provided valuable insights into the structural interaction between the existing superstructure and the elements of the retrofitting.

Prestressed concrete bridges built in the late last century are essential elements of the highway network. However they need to be retrofitted to ensure their continued operation under the increasing traffic loads. The retrofitting of these structures with external tendons requires the careful design of the end anchorage of the cables. The presently used anchorage concepts in Germany were investigated and evaluated. As a result some risks of this construction method could be identified.Based on this study new and improved end anchorage concepts were developed and their feasibility and effect on the existing superstructure was assessed. Finally the paper highlights crucial points in both design and construction of end anchorages for external tendons.