a design for an eco passage constructed out of logs over the Greenportlane
The eco passage is an important link in the ecological zone on the west side of the city of Venlo. It crosses the Greenportlane, the new main road of the large-scale development of Klavertje 4 (Clover 4), a new working landscape . The eco passage consists out of a pedestrian walkway and a bicycle path, making a combined width of 25 meters. The bridge is located at the Heijerhoevenweg, a road that crosses the Greenportlane under a slight angle of 15 degrees. The eco passage follows this angle, so the original historical line of the Heijerhoevenweg is kept in tact. Furthermore the eco passage has to contribute to image of Klavertje 4 as a Cradle to Cradle development. This is one of the reasons for constructing the bridge out of (indigenous) trees, which literally adds to the concept of nature crossing the road . The eco passage has to be realized before the opening of the Floriade (spring 2012), the biggest agricultural fair in the world.
Due to reasons of availability and material strength we have chosen for Larchen (Larix) for the columns and Oregon Pine for the deck. A double row of columns in the middle, two single rows on the sides and two concrete load bearing walls at the ends make up the structural design.
The beams are constructed out of 2 to 5 logs, which have a tapered shape. These logs, after removal of the bark, have a diameter of at least 300 mm and the width increases with 15 mm every meter. With a computerized mill the connection joints are precisely cut out, similar to a tong and groove connection. The logs are stacked on top of each other, turning them 180 degrees every other log. This enhances the strength of the construction.
The thickness of the soil which is needed for the plants and trees determines the height of the construction beams and therefore how many logs are needed. Because the thickness varies, the cross section is asymmetrical. This is why the eco passage has two slightly different sides. Also important for the height of the construction are the expansions. By placing the columns on an angle we manage to reduce the expansion at its most critical spot: there were the load of the ground is the largest (one and a half meters of soil). Here the columns are put on an angle of 30 degrees. Gradually towards the sides of the bridge the load reduces and the columns are placed more vertically, increasing the expansion between the columns. The structural concept of the asymmetrical deck together with the varying columns gives the eco passage its specific form and origami-like elegance.