Conceived as a ‘Kit of Parts’ With the Cruciform Arches
London based architects Useful Studio, with sister company Expedition Engineering, have completed a new footbridge in Chiswick, west London, spanning a live railway and nature reserve to link a business park with its nearest underground station.
Pioneering engineering drove the design to create a lean, simply detailed, safe and accessible piece of infrastructure. The graceful arches increase in height, in line with the significance of the spans, and present a natural form with the earthy tones of the materials complementing those of the adjacent nature reserve.
The network arch, an unusual development for footbridge design, is an efficient structural form. It solves the pedestrian dynamics and removes the need for dampers, allowing for the removal of substantial material from the arches. The crossing of the support cables provides additional restraint to the arches to aid in buckling resistance. The result is an extremely slender deck profile and an elegant tapering to the cross section of the arches. The bridge achieves long spans over varied terrain with minimum material use.
The tripartite plan allows the spans to gently curve, following the most efficient route between the landing points. These arches are formed from a cruciform section which continually changes in width and height according to where the material is needed for the optimum structural design. This rigor in collaborative design realizes a beautifully crisp arched silhouette, engineered and delivered through skilled fabrication.
The arched proposal is also a highly efficient form that maximizes off-site fabrication and safety during construction while minimizing disruption and reducing waste. This design ethos has been carried through from conception and into the design considerations for construction and demolition, embracing circular economy principles.
The bridge was conceived as a ‘kit of parts’, with the cruciform arches and their associated deck units erected from just five pieces, reducing the extent of complex on-site welding and working at height.
A ‘site-factory’ approach was adopted with off-line erection of all the bridge spans, including finishes and electrical installation, in a fully separated compound which minimized disruption to the Park. The fully assembled spans were then lifted into position – a safety driven approach that added to control of quality and critically, limited the railway possession to a very small window.
As far as practicable, a strategy of ‘zero maintenance’ was adopted with deliberate selection of materials, finishes, and components, and considered design of the details with whole life costing playing a central role.
The bridge is free for use and open 24/7 to create a fully accessible piece of infrastructure; the budget of £7.5million was not exceeded thanks to an efficient approach to design and construction.
By using less materials in its holistic design, adopting off-site construction methodology and forming a key walking link within both an urban and natural context, the bridge sets a new standard for beautiful, innovative and environmentally responsive infrastructure.
Project: Chiswick Park Footbridge / Location: London, UK / Lead designer: Useful Studio + Expedition Engineering / Lighting design: Speirs and Major / Electrical design: Atelier 10 / Access consultant: David Bonnet Associates / Landscape design: Charles Funke Associates / Project manager: Beadmans / Planning consultant: Jones Lang LaSalle / Steelwork fabricator: Severfield UK / Client: Blackstone Property Management / Completion: 2019 / Photograph: Useful Studio, Expedition Engineering, ©Jill Tait (courtesy of the architect), ©Sean Shumka (courtesy of the architect)
