An Exceptional Construction Project: The Wooden Arch Bridge in Sneek, Netherlands

In the northern part of the Netherlands, a quite unique traffic bridge was built over the A7 motorway for the city of Sneek: a wooden arch bridge. The basic design was developed by the architect Hans Achterbosch, who won a competition for innovative bridge structures.

The superstructure consists of two wooden arches carrying a steel deck. The bridge is 32m long, 16m high and 14m wide. The bridge consists of a special type of wood called Accoya^®. Thanks to special treatment, the ability of this wood to absorb water is greatly reduced, which is why it is suitable for permanent exterior use. All of the arch segments were manufactured by Schaffitzel Holzindustrie in Germany.

Individual segments were joined together into two separate arches on a building site along the A7 motorway. Afterwards, the arches were positioned using mobile cranes and integrated with the steel deck. Finally, the complete bridge superstructure was transported on a mobile platform and placed in its final position over the motorway. As the weight of the bridge was approximately 400t, a total of six mobile cranes had to be used during the installation.

DSI Netherlands was involved during the final design stage and was thus able to develop a suitable pre-stressing system with special anchors and transition elements for the joints between the arches and the deck. DSI supplied, installed, stressed and grouted all of the strand tendons needed.

Type 15,7mm, 1860N/mm² DYWIDAG Strand Post-Tensioning Tendons were used to absorb tensile forces at the ends of the arches.

Tendons with 10 strands were used longitudinally, and transverse tendons had 5 strands each. The anchor plates were exceptionally large in order to transfer pre-stressing forces into the wooden beams. Pre-stressing was carried out in two construction stages - the first one during the assembly of the individual arches and the second one during the integration of the whole bridge superstructure.

The acetyl preservation method used for the wood posed special requirements for the post-tensioning system because direct contact of the wood and pre-stressing steel would have accelerated the corrosion process. Consequently, the strands were double corrosion protected: they were installed in HDPE-tubes, which were injected with cement grout after stressing.

This exceptional bridge has become an important landmark for the city of Sneek. It not only gets the attention of local people, but also the attention of the international community of architects and civil engineers.

Schaffitzel Holzindustrie has already received an order for a similar bridge and is expecting additional projects in the future. DSI is proud to have contributed to the successful completion of this development.