New continuous 3-span concrete railway decks with extradosed post-tensioning cables in widening an existing multiple arch bridge

In improving the accessibility of the capital of Belgium by train, the railway company wants to increase the number of tracks from 2 to 4 tracks for the main railway lines in the direction of Brussels. In the urbanized and densely populated area near the capital, the design of the new infrastructure in extending the tracks, one on each side of the double track line, must be done with respect to existing historic bridges dating from the early 30’s. The paper describes the extension of a 3-span concrete multiple arch bridge over the canal Brussels-Charleroi by two new continuous 3- span concrete bridges with external post-tensioning and a total length of 102 m. The new one track superstructure is a fully concrete deck in U-shape having a width of 6,1 m and is continuous over 3 spans of respectively 30, 42 and 30 meter. Four extradosed post-tensioning cables make the construction a modern concrete structure contracting the existing arches. The paper describes the integral design of the railway bridge and the extradosed post-tensioning, as well as the construction method. In the design, special attention is given to the modeling of the post-tensioning cables taking into account that these cables are free from the deck in horizontal direction. The influence of this modeling on the cable force variation and the friction in the cables is considered. Finally, attention is given to fatigue in the extradosed cables. During and after the construction phase, continuing strain gauge measurements for a long period will be carried out in both the deck and the cables.