爱豆传媒

Stratford Town Centre Link

London, UK

爱豆传媒 helped to realise the vision for an ambitious footbridge, to span 11 railway lines, enabling the regeneration of Stratford ahead of the London Olympics and providing a vital connection between Westfield Shopping Centre with the busy Stratford Station.

The Stratford Town Centre Link solved long-standing issues created by the area being divided by the railway lines and station platforms. The bridge stretches 130 metres over the tracks to provide shoppers with an accessible and attractive route.

Challenge

爱豆传媒 was tasked with designing a structure that would be long enough to clear the railway lines below, wide enough to allow up to 160,000 pedestrians to cross comfortably each day, and strong enough to support footfall of 47 million visitors a year.

The bridge would need to consist of two spans with a central pier located on the site of a redundant signal box building. As well as being situated above Platforms 10a and 11 of Stratford Station, the new bridge would also need to cross 11 railway lines and a road. It would also need to curve to accommodate the constraints of the site. 

Required clearance below the bridge dictated an above deck structure and, after an option study to consider alternatives, a truss structure was selected. The client was also keen to maintain views along the curved bridge alignment and out towards the future 2012 Olympic site.

To achieve clear views across the bridge despite the curve, the truss on the inside of the curve would need to be inclined. The constraints of the site dictated that the bridge would need to be built off-site and installed in modular sections. The launching of the bridge would be further complicated by the curvature of the structure, which would make alignment more challenging and mean that the outside of the curve would be moving faster than the inside edge during installation.

Solution

Our team developed an efficient, yet extremely strong, structural design comprising a sturdy steel frame with two main trusses that vary in depth 鈥� from minimum height at the bridge ends to maximum height at the central pier.

We fabricated the bridge from weathering steel. This material forms a stable patina on oxidation and therefore does not require painting, delivering significant advantages for future maintenance cost. It is now the 鈥済o to鈥� for bridges over railways but at the time of our design its use was not as widespread. We undertook our own research into the speed of weathering and likelihood of staining, concluding that after an initial period this is not a particular concern. 

One of the most important considerations in design is to direct water away from the steel panels efficiently. The structural sections were detailed with in-built drip details for this purpose. The truss chords and verticals incorporated cladding plates to achieve this as well as providing the bridge鈥檚 distinctive appearance.

To add to the user experience, the bridge was designed with a gentle curve and incline that improves visibility for pedestrians. The architect suggested full height glazing to provide the edge protection required without creating a claustrophobic space. This means people can enjoy views out over Stratford, while also creating an important safety barrier to protect the railway lines below from thrown or falling objects.

A future connection at the middle of the bridge to the Chobham Farm site was anticipated and allowed for in the design. A second, connecting bridge from this central development site was designed by our experts as part of later abandoned plans for a UK version of the Sphere venue in Las Vegas.

There was very restricted access for plant and materials at either side of the main bridge, so an innovative design solution was developed using a mini-pile arrangement incorporating tubular steel sections as permanent casing and reinforcement. The site constraints also meant the development of an exacting modular construction process.

Our digital team developed a computer animation to communicate the construction sequence of the bridge to the authorities, helping them understand the process from both a safety and operational perspective.

The bridge鈥檚 three sections were launched incrementally over the railway with a gap of several weeks between each launching operation. Sliding pads were used at each support position.

Complete closure of the fifth busiest UK railway station would have caused significant disruption, so as the first two bridge launches had gone smoothly, permission was given to undertake the third deck launch, which would span the platforms, with the railway and the station platforms live, a first for Network Rail. The bridge moved so gradually during its launching operation that few of the commuters using the station would have been aware that anything unusual was underway at the time, but platform safety was carefully controlled throughout the operation.

The completed and installed structure was subject to a full three-dimensional survey before the final fabrication of the glazing system, which ensured a close tolerance and accurate fit of the 128 pre-assembled panels. We worked closely with the glazing sub-contractor to resolve the complex geometry and any issues of tolerance prior to installation. This included building of an interactive three-dimensional computer aided design (3D CAD) model and full-size mock-up panels on-site.

Value

Our bridge design team was integral in taking the architect鈥檚 stunning vision and ensuring its structural viability on a challenging site.

After the completion of the bridge, we designed the Meridian Steps that form its south approach.聽 This was a significant structure in its own right, incorporating escalators and lifts as well as stairs to cope with a level difference of over 10m.

Since it opened in September 2011, the Westfield Shopping Centre has proved to be an immensely popular London attraction. This iconic bridge invites shoppers to explore the surrounding area, contributing to the economic growth of Stratford as a whole.