Prototype Footbridge Spurs World Interest

Railways from France, Hungary, the USA, South Korea and elsewhere have expressed interest in the prototype Adaptable Bridge & Lift System. This modular stainless steel footbridge is designed to improve the passenger experience and exploit the latest industrial techniques to lower the environmental impact of production and maintenance and provide opportunities for British manufacturing.

The bridge aims to be ‘simpler, better and greener’ than current designs, according to Hazel Needham, Associate Structural Engineer at Expedition Engineering.

Infrastructure manager Network Rail currently installs about 20 new or replacement footbridges a year, according to Professional Head of Buildings & Architecture Anthony Dewar who has been investigating ways to increase this output. He told Rail Business UK that the modular design developed by the AVA consortium offers the possibility of higher production volumes and a new approach to procurement, with modules prebuilt and stored ready for use.

Construction could begin as soon as a contract is awarded, with an estimated total site time of 15 weeks of which installation would require a 36 h track possession; it is hoped that this can be reduced to 27 h. The target is an overall footbridge project timescale of 20 months from contract award to handover.

‘We anticipate a robust demand pipeline that leverages AVA’s design and construction principles, capitalising on manufacturing efficiencies through batch procurement, economies of scale, and incremental enhancements’, said Eva MacNamara, director of Expedition Engineering.

Seeking fresh ideas

The origins of AVA lie in a Footbridge Design Ideas Competition which Network Rail organised through the Royal Institute of British. Architects in 2018 in an effort to attract some fresh ideas.

Dewar said some existing bridges offer a poor passenger experience, and there has been little innovation in footbridge procurement, design or construction until now.

Network Rail felt there was the potential to further develop the design which had been selected as the runner up in the competition. This led to a spin-off project to produce a prototype which has now been erected on an industrial site at Sittingbourne in Kent.

Modular elements

The AVA bridge is designed to offer an ‘elegant and timeless’ design and to be suitable for ‘any station anywhere’, said Bob Atherton of steel supplier Outokumpu.

The modular approach reduces the time needed on site, ensures quality, is adaptable and provides economies of scale. ‘It should be straightforward to adapt the bridge for the vast majority of station configurations’, said Dewar.

The visible parts of the bridge are the actual structure, not cladding, with the main span being assembled from standard modules made from Forta LDX 2101 high strength duplex stainless steel plates. The steel is produced by Outokumpu using low carbon electricity, and processed by its UK subsidiary in Sheffield. According to Atherton, it has double the strength of typical stainless steel, enabling the thickness to be reduced without impacting on performance and meaning smaller foundations are required.

The steel is suitable for most locations in the UK, but a higher grade such as Forta DX 2205 with higher corrosion resistance could be used in more corrosive coastal or polluted environments.

The sheet steel is laser cut and folded to shape using ‘Industry 4·0’ manufacturing processes which are now well established outside the rail sector. The steel has inherent durability without needing painting, a bead-blasted permanent anti-glare treatment and is graffiti resistant.

The 1 200 mm long modules are joined together to form a maximum span of up to 20 m, with symmetrical custom length modules at each end of the span to provide the precise length required. The stairs are similarly modular, with the span above the landing modified to provide the required height.

The bridge is bolted together with using pre-loaded bolts supplied by Bumax which will not loosen over time. Assembly does not require specialist skills, and this approach simplifies maintenance; the bridge could even be dismantled and relocated if desired.

The walking surface is aluminium, which has a 25-year warranty and 60+ year design life with the ability to be easily replaced.

Network Rail is particularly keen to ensure that all critical parts of the structure are visible or easily accessible for inspection and maintenance. There is integrated lighting, and internal cable routes with hinged access panels.

Options include a roof, not fitted to the prototype, and privacy screens if there is a need to prevent users seeing over the side of the bridge.

The consortium expects the bridge to offer lower capital and whole-life costs than the current generation of footbridges, and even greater benefits over the full life cycle. A traditional bridge needs periodic painting, but there is always a temptation to delay this into the next budgeting period, meaning major work is required when the job is eventually tackled and ultimately leading to a shorter overall life.

The AVA bridge has an expected life of at least 120 years, requiring minimal maintenance which can be undertaken without requiring a track possession. ‘What you see today is what it will look like in 100 years’, said Atherton.

Accesibility

The AVA bridge is intended for use at stations, where passengers increasingly expect the provision of lifts for accessibility. However, it could be built without lifts.

The lift shafts are modular units, assembled off-site by ARX and delivered complete and ready for erection. This has reduced installation time from 26 weeks to 2 weeks.

The lifts draw on experience from the industrial lift sector. Features for reliability included two motors for redundancy, and a single section door. The motors are housed at platform level, rather than on top of the structure, facilitating simpler maintenance.

There are two layout options for the lifts. The narrow variant has the lifts in line with the stairs, and is suitable for locations with restricted space on the platform. The preferred wide variant has the lifts alongside the stairs, which takes up more space but eliminates the need for a wheelchair user to change direction. The prototype has one lift of each type.

Because the lifts are separate modular structures, they could be added to an existing bridge of an alternative design; studies are underway for a potential installation at Seven Sisters.

Prototype

The prototype bridge is a ‘version 0·9’, according to the project partners. Changes have been made based on the experience gained during manufacturing and assembly, and would be incorporated into production bridges from new.

One example is the laminated glass, which is designed to provide a more open feel than high steel sides. The glass is it at a slight angle to reduce glare, but this proved complex to install, and a simplified way of achieving the correct angle was developed to reduce costs.

When Rail Business UK visited the prototype on a hot day, the sunlight reflecting from the floor was dazzling, but production bridges would have a different deck surface treatment.

The first production AVA bridge is scheduled to be installed at Stowmarket in May 2025.

Source: Railway Gazette