Riverside Bridge
A pedestrian and cycle bridge in a classic tied-arch form with a twist: a split deck solution that serves both user agendas in a striking curvilinear structure A bridge for its time The first new bridge in half a century to be built on this, one of the UK’s most famously-bridged rivers, the Cam, had a lot to live up to. The Mathematical bridge, the 19th century St John’s College Bridge of Sighs, the 20th century Garret Hostel Lane Bridge: each celebrated as an achievement in its day, each cherished by subsequent generations as part of the particular mythology of Cambridge – any 21st century successor would have to meet the highest standards of beauty, appropriateness to context, and originality in order to earn its place on the river. Our competition-winning design for the new Riverside Bridge, with its refreshingly frank split-deck solution for segregating cyclists and pedestrians, captured the imagination of the voting public. Elegant in execution, sculptural in form, rigorously engineered to achieve a hard-working structure, the Riverside Bridge is a fitting addition to the unfolding architectural narrative of the Cam. The inspiration Cambridge County Council wanted a new bridge to provide a link from the town centre to a newly developed housing area on the north bank and also to serve the local sustainable transport strategy with an addition to Cambridge’s growing cycle network. Separating the cycle and pedestrian routes in a split-deck form set the structural and aesthetic agenda for our whole design. It was clear to us that two curved decks, supported either side of a tied arch, was at once the most visually striking and functionally suitable solution. It ensures the independent needs of cyclist and pedestrian users are met entirely on their own terms. The bridge form, meanwhile, describes a series of curves that are at the same time intriguing and pleasingly honest. Commodity The bridge rises in a gentle ramp over the floodplain on the north bank, sweeps across the river, then curves at a 90 degree angle to connect with a road running along the southern bank. The flowing curve of the bridge deck responds to the natural meandering of the river. With no sharp turns, steps or gradients steeper than 1 in 20, it is fully accessible for all users to enjoy. The arched form is well suited to the constraints of the site since it allows a very slender deck, minimising the length of the approach ramp which is needed to achieve the specified clearance of +3.6m over the river. On the approach ramps segregation between pedestrians and cyclists is suggested by a change of material in the deck surface. The pedestrian path is formed in lightweight perforated aluminium planks supported on cantilevered steel arms while the cycleway is a resin-bonded gravel surface on a structural steel box deck. Balustrades are in painted mild steel with stainless steel cables and handrails. As the bridge passes over the river the two decks split apart, with the arch rising between them. The cycleway continues to rise to a high point over the centre of the channel while the pedestrian route levels out, generating a ‘tiered’ section that provides an excellent vantage point for rowing events. The physical separation of the two routes over the river provides maximum safety for pedestrians at the point where they may wish to stop and enjoy the view. This is further encouraged by a widening of the pedestrian deck towards the centre. We gave special thought to how the bridge appears to a rower on the river; glancing up as he passes beneath the split deck he catches a glimpse of the sky. The northern approach ramp reverses the sweep of the bridge, its curved shape reducing its perceived length. In this ramp the geometrical discipline of the bridge becomes more relaxed and organic. Structural piers grow into sculpted lighting masts and small ‘pods’ off the main route provide resting places for pedestrians and cyclists. Firmness Steel hangers, suspended from the bridge’s arch, support the pedestrian deck while wishbone steel elements support the wider cycle deck. Careful analysis went into tuning this geometrically complex form to achieve the most streamlined, stable structure possible. Four tuned mass dampers are incorporated within the deck structure to mitigate dynamic oscillations, enabling the overall mass to be minimised. The challenge in constructing most bridges is how to erect the main span. Here, prefabricated components were assembled in the adjacent flood plain on temporary supports; the assembled structure, complete with its applied finishes, was simply lifted into position on its permanent piers during one afternoon. We worked closely with the fabricator, using 3D CAD and finite element analysis technology to ensure the individual components and their temporary supports were rigorously specified to serve the precise final alignment of the structure. Sustainability Constructed using largely recycled steel, the new bridge was conceived as the centerpiece for the local sustainable transport strategy. As such, it improves and promotes cycling across the Cam and creates a new route that widens user access. It has been embraced whole-heartedly by Cambridge’s enthusiastic cycle culture and is constantly in use. Delight In the words of Cambridgeshire County Councilor Matt Bradney, Cabinet Member for Growth and Infrastructure: ‘The bridge has really enhanced the area. It is a beautifully designed lightweight structure, cleverly constructed, which is distinct from but in the same tradition of high-quality as the historic bridges of the area. The elegant bridge and its approach causeways are now a highly significant feature of the landscape and encourage towpath use. It is a special and lasting contribution to the architecture of Cambridge.’ The bridge has won the following plaudits: - Winner, Design & Construction Category, British Waterways Renaissance Awards - Highly commended in the RICS East of England Community Benefit Awards - Shortlisted, BCI Awards

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