Architect: Tonkin Liu

Image: James Balston Photography, Lewis Brown

Undulating geometry

Swing Bridge, London

The unique circumstances of the Crystal Palace Park Dinosaur Islands and the need for a secure crossing inspired the structural artwork of Swing Bridge. The project delivers three specific innovations: swinging to access the banks, undulating geometry for structural strength, and the comb construction technique.

The 167-year-old, Grade I Listed concrete dinosaur sculptures at Crystal Palace Park were configured to depict extinct animals in the lost worlds of deep geological time. The bridge’s location helps to: mark the start of this sequence, to tell a story of evolution, which in turn inspiring the reference to the prehistoric bony fish, the precursor to the dinosaurs and the evolutionary timeline depicted on the islands.

Swing Bridge London
Imaginative design, digital manufacture, craft-based skills and galvanizing combine to provide a supremely elegant solution for Crystal Palace Park

Swing Bridge in LondonTo protect access to the Dinosaur Islands, the bridge has been designed to remain in the water and only make its connection to land when access is given for education and for maintenance. This negates the need for a large protective barrier, keeps its distance from the dinosaurs, and requires only one central foundation.

Crystal Palace Park in turn enjoys, when the bridge is not in use, a sculptural artwork floating in water. Form gives strength through geometry in each of the components of the structure. A triangular spine beam delivers load to the central bearing, its tailored form is minimised in response to the bending moments. The skeletal deck structure projects out from the beam’s backbone like form. The bridge form gains overall strength from being widest and tallest over its central support.

When the swing bridge is not in use, it acts as a sculptural artwork floating in the water.

Minimal thickness of the steel sheet is achieved by optimising resistance through the geometry. In the evolution of the first bony fish, an undulating movement produces a force that propels it forward. The form of the balustrade and deck resists forces applied to the handrail through a push-pull action. The balusters lean backward and forward along the length of the deck, the outer acting as a strut and the inner acting as a tie. The multiple bent and welded prongs act together like spokes in a wheel to give the structure lateral stiffness. The frequency and pitch of the oscillation have been engineered to find the optimum form.

Swing Bridge Structure
Material cost and wastage was reduced by utilising the whole surface of the 10 mm steel sheet. The plate was laser-cut to prongs of three different lengths to form the bridge deck support strut and balustrade.

Responding to budgetary constraints and drawing on the iconography of the bony fish, Tonkin Liu proposed the laser-cut skeletal comb structural technique. The plate is laser-cut to prongs of three different lengths. One prong remains flat to form the bridge deck, one is bent up to form the balustrade, one bent down to form a strut to the lower edge of the central beam, utilising the whole surface of the 10 mm steel sheet. This minimises material cost and wastage, reduces the amount of welding by
50%, and allows for the direct expression of strength in sculptural form.

Swing BridgeThe project was instigated by the long-standing commitment and insightfulness of the Friends of Crystal Place Dinosaurs, who raised funds from the GLA and crowdfunding, and delivered, through close collaboration with architects Tonkin Liu, engineers Arup, and locally based fabricators, Cake Industries.

The scheme spans the gap between precise digital manufacture and craft-based skills. Cake Industries developed prototypes and models to feed into the design, to ensure that the innovative processes were achievable. A full object-based 3D model of the structure was then generated to define the cutting patterns for the laser cut steel. Once laser-cut, the steel sheets arrived in flat pack form ready to be manipulated by the fabrication team to create the undulating geometry.

Individual areas were heated with an oxyacetylene torch to allow the comb to be bent into shape. The fully welded assembly was brought together into one piece, before being hot dip galvanized to provide long-term durable corrosion protection.

(Content provided by Tonkin Liu)

Engineers | Arup
Fabricators | Cake Industries

Architect: Tonkin Liu

Image: James Balston Photography, Lewis Brown

Posted on September 8, 2021 by Galvanizers Association

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