Bridges in Africa constructed using DYWIDAG Strand Tendons

Steinmetz Flyover, Cotonou, Benin

Several rivers along the tropical coast of the western African state of Benin exit to the sea by forming lagoons. Cotonou, a city that has grown to become the largest in Benin, is also divided by a lagoon. Cotonou features the country’s largest harbour and is the economic center of Benin as well as the country’s seat of government. The city’s strong growth has resulted in a considerable increase in traffic volume on each side of the lagoon. Additionally, the main route along the western African coast also leads through Cotonou. In order to cope with the increase in traffic volume, three new bridges were built over the lagoon’s outflow channel into the sea.

All of the traffic that crossed the lagoon via the Konrad Adenauer Bridge, a four lane bridge structure completed in 2004, in the past was directed to the Steinmetz roundabout at the western end of the bridge. Because one of Cotonou’s main roads also connects to this roundabout, lengthy traffic obstructions occurred on a daily basis. These traffic jams have now been eliminated by the construction of an overpass over the Steinmetz roundabout. Now, traffic flows across town much more fluently. In addition, this important traffic junction has now become considerably safer for all road users.

The inner-city bridge designed to alleviate the Steinmetz roundabout congestion is 180m long. The access ramps to both sides of the bridge measure 50 and 120m in length and are 15m wide. The bridge accommodates one lane for vehicles as well as a special lane for two-wheelers and a narrow sidewalk into each direction. In order to eliminate the traffic obstruction as quickly as possible, a short construction time was paramount. That is why the bridge was constructed using the prestressed concrete method.

First of all, the contractor, DYWIDAG International GmbH, concreted the piers together with the crossbeams. After the completion of all of the piers, concreting began for the 9 bridge spans in lengths of 20m each using false work. In order to achieve the required structural capacity of the bridge, 18 DYWIDAG strand tendons with one type MA-A 6815 stressing anchor and one type MA-B 6815 fixed anchor each were installed per superstructure segment. The strands were inserted into the ducts before concreting. Afterwards, the concrete for the superstructure segment was cast, and once the required concrete strength was achieved, the tendons were stressed using a HOZ 5,400 bundle jack. Finally, the ducts were injected with cement grout to achieve bonding between the strands and the superstructure and to protect the tendons against corrosion.

DSI delivered DYWIDAG Post-Tensioning Systems for this important inner-city bridge. The new Steinmetz traffic hub was opened to  traffic at the end of 2008 following a festive ceremony at which both Benin’s president and the German ambassador were present.