Last month, Crystal Palace Park in the London Borough of Bromley installed a functional piece of structural artwork dubbed Swing Bridge. Led by architecture firm Tonkin Liu Architects, the design team created an 8 m long, undulating, geometric piece of galvanized steel art that utilizes laser-cut comb construction. When desired, the installation can also be rotated to provide pedestrian access to the park’s historic Dinosaur Island.
The island, visible from shore, is populated by 167-year-old concrete dinosaur sculptures and constructed geologic strata depicting three geologic eras: the Precambrian and Lower Paleolithic, Upper Paleolithic-Upper Cretaceous, and Tertiary and Quaternary. The statues and constructed geologic strata are Grade 1 listed by the public governmental body Historic England. (This preservation listing is the highest offered and is reserved for those areas and structures of the highest national importance and significance).
Access to the islands will be limited to educational and maintenance trips, with the crossing typically rotated so that it functions as a sculptural artwork above the lake’s waterline.
The geometric shape of the crossing is drawn from the iconography of a bony fish and gives the crossing much of its strength, enabling the steel sheets to be as thin as possible at just 10 mm thick, explain the architects in material distributed about the design. This plate was laser-cut in three different lengths: one prong remained flat to create the bridge deck, one prong was bent upward to form the balustrade, and one was bent down to form a strut to the lower edge of the bridge’s central beam. Shaping the plate in this manner minimized the cost of materials, reduced the necessary welding by 50%, and allowed for the “direct expression of strength in sculptural form,” according to the architects.
“The undulating form of the balustrade and deck resists forces applied to the handrail through a push-pull action,” explain the architects. “The balusters lean backward and forward along the length of the undulating 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 undulating form lateral stiffness. The frequency and pitch of the oscillation have been engineered to find the optimum form.”
The triangular spine beam to which the plate is attached delivers the bridge’s gravity load to the central bearing support, which is founded upon piles within the lake.
Commissioning client Friends of Crystal Palace Dinosaurs
Part-funding client Greater London Authority
Architect Tonkin Liu Architects
Structural engineer Arup
Main contractor, fabricator, and substructure design Cake Industries
Galvanizing subcontractor Joseph Ash Galvanizing
Piling design Michael Aubrey Partnership Ltd
Piling contractor Capital Piling Ltd