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Rising to the challenge

Transport Birmingham airport

The pioneering maglev people-mover at the UK's Birmingham International Airport proved to be a flop. Now an alternative developed in a Las Vegas casino is about to go into service, as Alan Sparks reports.

Transport 1,500 passengers an hour, plus luggage, 600m horizontally in the most comfortable, efficient and reliable way. This is the challenge that has been facing Birmingham International Airport for the past couple of decades.

A twin track magnetic levitation (maglev) transport link was opened in 1984 to move travellers from the terminal to the nearby rail station. Such a link made the airport more attractive to investment and increased its public profile. But the system soon became an albatross around its neck, dogged by reliability and maintenance problems.

With few similar systems elsewhere, replacement parts were difficult or impossible to get hold of, with engineers often having to modify parts to paper over any cracks.

Finally, in 1995 the airport unveiled a 10 year development plan and a replacement system was sought. A succession of alternatives failed to satisfy the team until the answer was found, in a Las Vegas casino.

A horizontal cable car at the Mandalay Bay Resort performs at an efficiency of 99.5% in transporting punters around its mammoth complex. The system's manufacturer and German cable car operator, Doppelmayr, was recruited to develop a similar system for Birmingham.

Costing over ú10M (US-14M), the 20 year design, build, finance and operate cable car project will carry up to 1,500 people per hour over the 600m distance in 90 seconds. Babtie performed all civil and structural design work with all civils work done by contractor, Fitzpatrick. Austrian specialist outfit Mayer completed all work relating to the track.

Elevated above ground level, the concrete track for the original maglev system was supported by a concrete viaduct spanning over highways, car parks and drop off areas. The same route and supporting structure was to be used for the cable car system, with the original trackbed removed and replaced by steel trusses. With no increased loads on the original viaduct, no structural adjustments were deemed necessary.

Closures and diversions were required when tackling the highway crossings as a 650t crane shifted trackbed sections weighing as much as 55t. 'By removing the maglev's old slabs in such large pieces and breaking them up later, massive time savings were made, ' explains Fitzpatrick project manager Shaun Wake. The task took 'two or three days rather than a couple of weeks', he says.

Extensive craning throughout the job meant that the contract was the largest single element of Fitzpatrick's section of the works. The new steel trussed supports were prefabricated in Austria and brought over at preplanned intervals.

However, these supports, with the necessary special bearings or shoes, together made the track level 1.4m higher than the old system. At each end of the run the track must drop down to meet the original platform levels, with supports in these areas amended to suit.

Fitting the shoes on to the original pillars proved to be one of the most testing parts of the job for Fitzpatrick. The concrete had matured to a compressive strength measured at 100N/mm 2.Eight dowel bolts and 12 dowel bars were needed to transfer shear from the shoes into the heavily reinforced supports.

Supplied drawings of the existing piers were all but useless as up to 200 pilot holes were needed on some piers to find enough room for the connectors.

'In some spots we had to break out the concrete and bend the rebars to find enough space to drill the holes, ' explains Wake.

With an S-shaped track plan, lateral forces from the cars were further restrained by the addition of 3m long carbon fibre-reinforced polymer strips on the outside of the curves - resisting compression forces as the track attempts to straighten itself out under load.

These forces and temperature effects are combated through typical movement joints, with automated hydraulic rams to ensure cable tension remains constant.

Disturbance to airport business was to be kept to a minimum throughout the contract.

Sections nearest to the airport proved the most awkward where supports of 14m lengths needed to be craned into position over the taxi ranks and the drop-off point for the terminal.

The platform was removed as the members were placed, then rebuilt around the new track support. But with extra shear connectors 32mm in diameter, finding enough space in the matrix of reinforcement for the shoes proved impossible. The solution was 'to fit these in wherever we could', says Wake.

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