Vihantasalmi Bridge

The bridge crosses the Vihantasalmi Straits that are located in the municipality of Mäntyharju on highway no. 5. The new bridge was completed in September 1999 and replaced the old run-down steel bridge.

When plans were made to build a new bridge, the idea was proposed that this scenic location deserved a wooden bridge that would reflect the importance of the area as a source of timber and a base for the wood industry, and to enhance the area’s ecological image. As the project was extremely demanding both in terms of construction techniques and visually, a design competition was organised to find the best solution.

The first prize went to a team put together by the engineering firm Rantakokko & Co Oy for its entry entitled ”Honkahimmeli” (a timber structure that resembles a traditional Finnish Christmas decoration made of straw), of which the judging panel said as follows:

”The winning entry is respectful of the traditions of wood construction but at the same time modern in its application of today’s technology. The design successfully combines clean structural lines and practicality with an aesthetically high-standard appearance that brings the essence of timber structures to the fore.” The final design was based on the winning entry.

Technically, the three mid-spans consist of a truss-framed structure made of glue-laminated timber while the end spans are timber-concrete composite beam bridges. The spans are 21 + 42 + 42 + 42 + 21 = 168 m. The carriageway is 11m wide and the pedestrian and bicycle path 3.0 m wide. The total length of the bridge is 182 m, and the clearance under the deck it is 4.0 m.

The basic idea of the bridge drew upon traditional bridge engineering but its dimensions made it a highly demanding task. The distance from the surface of the lake to the highest point of the bridge is approx. 31 m. As far as is known, this is, in terms of surface area, the world’s largest wooden bridge ever built on a highway. Compared to the longest wooden road bridges previously built in Finland, the span of this new bridge is twice as long.

When the bridge was designed, use was made of the results of the latest research and development work on wooden bridges. This research work has been carried out jointly by the National Road Administration and the Helsinki University of Technology since the late 1980s and within the framework of Nordic co-operation since the 1990s. Additionally, fatigue testing on the dowels used in the timber-concrete composite beam bridge was carried out to verify the performance of the selected dowel types and adhesives.

Innovative solutions were also required in the superstructure of the truss-framed bridge where a combination of wood, concrete and steel was employed. In particular, the design of the numerous jointing details required major work input.

Finnish Wood Award 2000