Built Expressions Bangalore :: Slinky Springs To Fame, Germany

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Slinky Springs, Germany

Spiralling Ecstasy

The elegant pedestrian bridge across the Rhein-Herne canal in Oberhausen, Germany is a part of the art project "EMSCHERKUNST 2010". Following the design of the renowned artist Tobias Rehberger, a colourful ribbon wrapped in a light, swinging spiral connected the Emscher Island with the Kaisergarten Park. The bridge was completed in the year 2011 creating a new way in the contemporary architecture.

Schlaich Bergermann and Partner, one of the leading structural engineering firms in Germany provided the structural consultancy for the project. Mike Schlaich, partner of the firm closely monitored the project and successfully completed it. Speaking to Built Expressions, Prof. Mike Schlaich shared his learning experience, working on one of the landmark projects.

Bridge Sculpture

The artist, Tobias Rehberger, envisioned a colourful ribbon wrapped in a wild, swinging, erratic, and monumental spiral that would connect the existing parks and undulate over the canal like a rope flung across the water.

Explaining about the core details of the project Prof. Mike Schlaich says, "Initial tests on the technical feasibility of the artist's idea showed that the spiral, which was supposed to appear as light and vibrant as possible, could not act as support structure for the sculptural bridge. The solution proposed was to use the band which is also part of Rehberger's sketch, to achieve the desired effect of a light and vibrant sculptural bridge was to build a minimalist version of a stress ribbon bridge as supporting structure. The spiral could then be bolted to the bridge, and being independent of the supporting structure would only have to support itself."

Landmark Project

Sharing his experience working on this impeccable project, Prof. Mike Schlaich says, "The result structure of the bridge enabled the implementation of the artistic concept and, as desired, made the bridge appear as a work of art. We would like to emphasise the successful collaboration between civil engineers, the artist, and the open-minded client. Finally, we appreciate - much more than to complete a 'landmark projec' - to see how good the pedestrian bridge is adapted in the landscape and especially accepted by the user."

Basic Design Conditions

The sculptural bridge had to be fitted carefully into the sensitive surroundings. For various reasons, the banks along the canal could not be heavily loaded with structure. The canal banks are secured with anchored steel bars that couldn’t be altered or adapted. Several supply lines also run along the Rhein-Herne canal paths. This made it impossible to build foundations for the main bridge directly next to the canal.

To satisfy the Waterways Authority (Wasser- und Schifffahrtsamt) requirement of a minimum 8 metre clearance for container ships, the stress ribbon bridge has to pass over the canal at an unusual height of about 10 metres. Apart from the artistic aspect, unimpeded usability and accessibility of the bridge are also important design criteria. Ramps at a constant gradient of 6 percent were planned on both sides of the stress ribbon bridge to allow pedestrians to negotiate the difference in altitude. The ramp lengths required by this limited gradient were accomplished by giving them curved forms. The 170 metre long ramp on the southern canal bank is directed through the trees of the Kaisergarten in an s-form and then levels off along the Waldteich lake on the visual axis to Schloss Oberhausen. The approximately 130 metre long ramp on the northern canal bank has a u-shape and ends near the bank where it meets the pedestrian and bicycle traffic on the canal path.

Collaborating with landscape architects Davids | Terfrüchte + Partner, the ramps were integrated in such a way that the largest possible part of the existing tree cover in the Kaisergarten could be saved.

Stress Ribbon Bridge

To keep the span of the main bridge across the canal to a minimum, it was designed as an elegant and lightweight three-span stress ribbon bridge with a span of 66 metres in the middle span and 20 metres in the two side spans.

Commenting on the usage of high strength steel, Prof. Mike Schlaich elucidates, "Two most slender ribbons made of very high-strength steel (S690) run across the columns inclined towards the canal and are anchored on the columns inclined away from the canal. The resulting tension force was then transferred into strong abutments through the outer vertical tension rods. The saddles on the heads of the steel columns are shaped accordingly to reduce bending stress on the ribbons."

The walkway consists of 2.67 metre wide and 12 centimetre thick pre-cast concrete panels, bolted to the stress ribbon, to which the railings, consisting of cable nets, steel posts and steel tubing, as well as the spiral are attached.

All stress ribbon bridges are prone to oscillation, because they are the lightest and therefore, most dynamic way of constructing bridges. Therefore, the dampening characteristics of the cable net railings and the springy, synthetic pavement were used to absorb the vibration of this bridge, and dampening elements were arranged between the pre-cast concrete plates. The possible dampening characteristics of the spiral were not used.

According to Prof. Mike Schlaich, the use of high-strength steel S690 for the two stress ribbons has approximately the double strength of standard steel. It enabled the very slender and light appearance of the bridge, since the use of normal strength steel would have caused much heavier steel plates.

The structure required wind tunnel tests and complex dynamic calculations. The supports inclined towards the canal were stiffened with diagonals and bracings to reduce horizontal deformation of the stress ribbon bridge from wind loading.

The tension of the stress ribbons and the pre-strain of the supporting steel structure were chosen such that the dead load of the structure would produce the planned geometry of the bridge.

Ramp Bridges

The ramp bridges extend on both banks on slender vertical steel columns. The ramp bridges are rigidly connected to the stress ribbon bridge. The superstructure of the ramps was constructed with 25 centimetre thick concrete slabs. The individual spans of the segments come to around 10 metres. Bracings of fine tension rods stiffen the unusually high bridges against horizontal loads. Along the Waldteich in the Kaisergarten, V-shaped supports increase clearance from the footing and avoid footings in the water.

Spiral Structure

The complete footbridge was wrapped in an undulating spiral (5-metre diameter) made of an aluminium hollow section bolted to the bridge’s structure. For the technical realisation of the complex 3D geometry of the spiral, individual modules were developed that were then combined to create the desired geometry.

Lighting Concept

At night, the dark spiral vanishes into the background, and the superstructure takes its place, meandering through the park in a radiant and colourfully perceptible way. Colours need a lot of light - sufficient, bright and brilliant white.

The use of colourful light gives a vibrant look to the bridge. Elaborating on the usage of LED lights, Prof. Mike Schlaich asserts, "LED lamps were used consistently; another delightful advantage for day and night impression is that these slim LED lamps could completely be incorporated into the bridge's structure: on top of the bridge in the railings, and underneath the bridge at the low points of the spiral. Shining at the cool colour temperature of 7,300 K - daylight white - the highly efficient lamps are mounted almost invisibly and guide pedestrians across the colourful paving. Due to the quality of lamps and light, the colour is as brilliant as can be. Looking at "Slinky springs to fame" from afar, the impression is that the bridge is giving off light itself."

The night illumination with colourful pavement pathway was meticulously planned in order to match the colours on top as well as bottom. “The springy synthetic pavement as well as the colourful rhythmization of both concrete and coating amplifies the dynamic experience of the bridge. For the pavement, a synthetic and elastic seamless floor covering system has been used as it is normally used for protection on playgrounds. The wear layer is consisting of solid-coloured EPDM granules mixed with a PU bonding agent. The base layer is consisting of SBR granules mixed with a PU bonding agent. It was important to integrate the lighting well, so that during daytime only a minimum of cables and the light is visible,” says Prof. Mike Schlaich.

At the outset, a colourful pedestrian bridge which was inspired by a toy has been transformed to a new landmarks in Oberhausen, Germany. Due to its unique design, it is been truly acclaimed by the users and has set the standards for the modern architects.

Project Details

Location Oberhausen, Germany

Type of Structure: Stress Ribbon Bridge

Owner: Emschergenossenschaft

Completed: 2011

Contractors: ARGE Stahlbau Raulf; IHT Bochum

Cooperation: Madako, Oberhausen

Technical Data

Total length: 406 m

Span: 20 m - 66 m - 20 m (Stress Ribbon Bridge) 10 m (ramp bridges)

Lengths of the ramps: 130 resp. 170 m

Bridge Width: 2.67 m