Frame and Form

Last 15 April a new bridge was inaugurated in the Dutch city of Sneek. The sexy wooden structure attracts attention of drivers on the motorway A7 passing beneath. This design represents an important step towards the use of sustainable materials in the higher-level structures.

It all started when the government of the Netherlands province of Friesland and the Public Works Department expressed the desire to use more wood in their buildings. The team chosen to design the bridge took on the challenge of creating a responsible and sustainable bridge that employ the latest technology in the wood industry to create a milestone in the motorway A-7 by the town of Sneek. The result of close collaboration between the construction company, the government and the architecture offices of Onix and Achterbosch is the first wooden road bridge designed to withstand traffic loads as standard Eurocode.

entrance to the bridge view

The bridge is built plywood Accoya the Titan Wood, acetylated wood is, which means that the wood has undergone a biochemical process that seals improving dramatically its durability and hardness. This technology achieves a high performance material that comes from certified sustainable sources. This is a non-toxic recyclable and biodegradable.

detail finishes

The bridge is part of the action to reform the Highway A7 and already there are plans to build a second bridge in 2010. Thus drivers will have a clear perception and pleasure from their stay in Sneek while local citizens are guaranteed the permeability of its territory ‘doors’ center communicating with the neighboring districts.

detail finishes

The bridge has a length of 32 meters, width 12 meters and rises 16 feet above the ground. Allows passage of traffic, pedestrians and cyclists. It is designed for a lifetime of 80 years with moderate maintenance. The wooden beams reach 1080 x 1400 mm of solid section. They are designed prestressed joints between the main elements.

detail finishes

The structure consists of two main orders. The first, formed by a pair of triangular frames are curved in cross section to allow passage of vehicles. And the second, families formed by two diagonals that are interlaced within the frameworks. Although the authors consider the possibility of making the board timber, concluded that the width of the bridge and its loads require a song 2 meters in the transverse beams so I finally opted for a more classic steel.

detail finishes

detail finishes

One of the most interesting aspects of the design process is how the authors have worked on new material taking advantage of their interesting physical properties. On the one hand, as already discussed, Accoya wood allows the durability needed in a type of work like this, but otherwise the work of plywood allows the construction of components with complex geometries such as double-curved surfaces.

watercolor

As shown in the following images, las excelentes propiedades flexibles de la madera permiten realizar una predeformación del conjunto de láminas antes del encolado de las mismas y su discretización en diferentes piezas asegura que el nivel de tensiones no es excesivo lo que limitaría la capacidad portante del elemento en servicio.

laminated single and double curvature

finding new ways on plywood

Following, we can see different pictures of the process of making the model. This process is important in the development of the project because it facilitates the possibility of thinking about how construction and assembly of the elements. A good designer must take into account the complexity of building the structure so that its implementation does not interfere with the final quality of the work.

assembly model

assembly model

model

Below these lines, Bridge project plans. Where can appreciate the different parts of the structure as well as studies of uses and gauges.

standard level bridge

bridge cross-section plane

Finally, we leave you with a photographic record of the bridge construction process. It is fascinating to see how the major elements were made of wood in the nearby industrialized workshops Titan Wood then be transported to a work area near the site of the bridge.

construction process

construction process

construction process

construction process

Interesting detail of the prestressed beam joints between the main board and the diagonals of the triangular frame. This may be the key node of the structure since it must collect large triangular frame compressions and breaking them down into the vertical reactions at the abutments and the great strain of the beam ‘tirante’. Ultimately the bridge works in several ways as a arco bowstring.

construction process

Once assembled various components of the bridge the main parties are ready for assembly and form the bridge. This construction process allows work on several fronts. On one side was launched carrying out the work of reinforced concrete substructure of the foundation, abutment walls and the cell. On the other mounting on site workshop and metal board and wooden superstructure.

construction process

In the next photo you can see the three main elements of the bridge ready for assembly. The two lattice frames and board will unite to form the substructure to be transported to its site completely built around low-end 200 meters.

construction process

construction process

construction process

The dramatic shift operation over the bridge and placement on the substructure was made in one night in order to interfere as little as possible the highway traffic.

construction process

construction process

construction process

Technical Work:

Location: Sneek. Netherlands
Design: OAK Architects (a collaboration of Behind Bosch Architecture and Onix architects)
Builder: Schaffitzel timber industry
Promoter: A7sneek
Wood Supplier: Titan Wood
Budget: 3,5 million €
Design Competition Award by: 2005
Date of completion of work: 15 April 2009
Span between supports: 32 m

Meta-Information

Video of the process of lifting and placement of bridge. Really interesting!
Article on the acetylation process and green properties of wood Accoya, by the Technical Director of Titan Word [Eng]
Article about the lifting and transporting the bridge in the journal KHL [Eng]
Subjective video from a car on the highway passing under a bridge