Seismic Stability with Bars: The Haspelbaechel Viaduct in Lorraine
The Haspelbaechel Viaduct is located in the Vosges Mountains near the Alsatian Plain. As part of the East European High Speed Line, it links Paris with eastern France and southern Germany. Since railway lines for high speed trains may only include very small curves, the section across the Haspelbaechel valley was built as a 270m long viaduct with 40m high piers.
In order to minimize the environmental impact on the Northern Vosges Nature Park, the viaduct was built with five spans with lengths of 58m each. Recently, the hollow box girder bridge deck, which had been originally built in 2001using the cantilever method, was transformed into a double steel beam structure as a result of new seismic design regulations.
Within the scope of the seismic rehabilitation, the bridge abutments were stabilized using 6 horizontal Ø 75mm DYWIDAG Post-Tensioning Bars. The post-tensioning bars had to be tensioned in accordance with a very specific predefined sequence in order not to destabilize the abutments. First, the DYWIDAG Post-Tensioning Bars were individually tensioned to 50%. Afterwards, they were tensioned to their final post-tensioning force of 300t.
Following a request of the general contractor Eiffage Construction Métallique, a test was carried out at the 50% tensioning level using a load measurement sensor in order to prove that the bars were being tensioned correctly. This test required the approval of two different engineering offices. After the successful completion of the tests, the DYWIDAG Post-Tensioning Bars were tensioned to their final loads.
The accuracy of the installation was particularly important because this was the first time such an abutment rehabilitation was being done in France. Consequently, the Post-Tensioning System only had a total load allowance of 5%.
The DYWIDAG Post-Tensioning Bars used in this project were restressable bars in ducts that had been injected with wax. In order to test the completeness of the bars’ corrosion protection and to make sure there were no leaks or permeable connections between the injection port and the vents, the impermeability of the ducts was tested using compressed air before injecting the wax.