First Swiss wildlife bridge made of wood

18.11.2020

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It took a long time to convince: Over 20 years ago Stefan Zöllig showed that wood is the right choice of building material for green bridges. Now it is built, the first wild animal bridge with a wooden roof. More will follow.

There are 305 wildlife corridors of national importance in Switzerland. Many of them with unfavorable conditions for the animals, such as impassable highways, busy cantonal roads or railway lines. Because traffic routes cut through the wildlife habitats, the Federal Office for the Environment has defined such wildlife corridors of supra-regional importance. Corridor "AG6" connects the Jura region with the Central Plateau and runs between Gränichen and Suhr on the A1 motorway. A 50-meter-wide arch structure will soon enable wild animals to cross the motorway safely.  

WIldtierbrücke Rynetel

Around 70,000 vehicles pass the wooden bridge every day.


Timbatec has been committed to wooden wildlife bridges for over twenty years. In 1998, a basic report using the example of the Chüsenrain green bridge in Neuenkirch (Lucerne), showed that wood as a local raw material is a cost-effective and ecological alternative for green bridges. This report was written by Stefan Zöllig on behalf of the Swiss Society for Wildlife Biology for the Swiss Ornithological Institute Sempach. In 2005 the Department of Construction, Transport and Environment of the Canton of Aargau commissioned moser+colombo architektur gmbh and Timbatec with a concept study. The result was clear: wildlife overpasses over motorways can be easily realized with a wooden supporting structure despite high earth loads and impact forces. 


Comparison wood vs. concrete

In the pre-project phases, the concrete and wooden versions were compared. In addition to the economic efficiency, the construction should be low-maintenance and durable and last for 100 years. A later extension from two to three lanes of the motorway must be possible. The flow of traffic on the motorway must be guaranteed at all times, even during the construction period. Timber has finished better in this comparison. In the end, the decisive factors were the better ecological balance and the shorter construction time.


CO₂ storage 

One cubic meter of wood relieves the atmosphere by about one ton of CO₂, because trees convert CO₂ into oxygen and carbon during growth thanks to photosynthesis. According to KBOB, the production of one cubic meter of reinforced concrete, on the other hand, causes around 500 kilograms of CO₂. Wood is thus clearly ahead of the rest when it comes to the climate issue.

WIldtierbrücke Rynetel

The execution of the wildlife transfer in concrete would have caused a CO₂ emission of 520 tons of CO₂. With the realized wood version, 210 tons of CO₂ were emitted for the production of the glued laminated timber and for the production of the steel joints. At the same time, thanks to photosynthesis, the wood used stores 775 tons of CO₂. Net 565 tons of CO₂ are stored in the Rynetel wildlife bridge. The difference between the wood and concrete version is therefore 1'085 tons of CO₂!     

The 850 cubic meters of construction timber for the wildlife bridge in Suhr grow back in the Swiss forest within 3 hours and 26 minutes.

Production and assembly

ARGE FERA, together with Aarvia Bau AG and Häring AG, was commissioned with the execution. The required 156 BSH arched beams were prefabricated at Hüsser Holzleimbau AG in Bremgarten. The beams are 17.4 meters long, have a cross-section of 24 by 76 centimeters and weigh two tons each. For this purpose, spruce boards were glued dimensionally stable with a large glue press and an RF adhesive. Steel joints, so-called metal shoes on both sides of the beams, provide the necessary supports for the assembly. 


WIldtierbrücke Rynetel

Production of glued laminated timber at the company Hüsser Leimbau AG


For the installation of the girders, the motorway was reduced to two lanes during 24 nights from 9:30 p.m. to 4 a.m. In the week from 26.10. - 30.10.2020 the sealing work will be completed. By the end of 2020, the wooden bridge will then be completed with root protection foil, seepage debris, drainage mat and soil for planting.  


WIldtierbrücke Rynetel

The assembly took place at night. Traffic continued on the other lane.


Facts and Figures

- Spans: 2 x 17.4 meters 

- Length: 35.6 meter (transverse to the road)  

- Width: 54 meter (lengthwise to the road) 

- Bridge area: 1922 m2  

- Construction costs: 13.9 million francs 

- Construction timber: 850 m3 spruce, origin Switzerland  


- Client: Federal Roads Office ASTRA, Zofingen branch   

- Planning: Engineering consortium WUEF; Bänziger Partner AG and Timbatec Holzbauingenieure Schweiz AG    

- Execution: ARGE FERA with Aarvia Bau AG and Häring AG

- Glued laminated timber supplier: Hüsser Leimbau AG 

WIldtierbrücke Rynetel
WIldtierbrücke Rynetel

Above: View from the roadway to the beams

Below: Detail support of the wooden beams on the in-situ concrete wall

 
 
 

Switzerland:

Headquarters

Timbatec Timber Construction Engineers Switzerland Ltd.

Niesenstrasse 1, 3600 Thun

Tel: +41 58 255 15 10

thun@timbatec.ch


Zürich Branch

Timbatec Timber Construction Engineers Switzerland Ltd.

Ausstellungsstrasse 36, 8005 Zürich

Tel: +41 58 255 15 20

zuerich@timbatec.ch


Bern Branch

Timbatec Timber Construction Engineers Switzerland Ltd.

Falkenplatz 1, 3012 Bern

Tel: +41 58 255 15 30

bern@timbatec.ch

Austria:

Headquarters Vienna (A) 

Timbatec Timber Construction Engineers GmbH
Im Werd 6/31a, 1020 Wien 
Tel: +43 720 2733 01

wien@timbatec.at


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