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Rising to the challenge

Airports Birmingham

Birmingham International Airport's pioneering maglev people-mover 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 the public, increasing Birmingham's profile.

But the maglev system soon mutated from the apple of the airport's eye to 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, surprisingly, 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 £10M, 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. As there was to be 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.

As minimising disturbance was vital, the speed of this method justified the extra cost.

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.

This unexpected hindrance threatened to prevent Fitzpatrick meeting its deadline to have the shoes in place before the track support trusses arrived. But by pulling together the team met all deadlines and the project was delivered a fortnight early, and within budget.

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.

Worst case load tests, used to assess any impact on the buildings at each end from emergency stop induced forces, showed that these would prove structurally sound. These forces and temperature effects are combated through typical movement joints, and automated hydraulic rams are used to ensure cable tension remains constant.

Disturbance to airport business was to be kept to a minimum throughout the contract, which ran throughout last year.

Sections nearest to the airport proved the most awkward where the existing structure passes over a newsagent and coffee shop and needed to be broken out to receive the new structural elements.

With the original concrete exposed, the team realised that extra work, time and expense was needed, with the strict deadline arrival of the Austrian elements fast approaching.

Supports of 14m lengths needed to be craned into position over the taxi ranks and the drop-off front of the terminal.

'This demanded complete planning. Taxi drivers, police, the airport and anybody else who would be affected were fully notified and provided for during the work. A full shift of staff was on site that night to ensure public safety and security, ' says Wake.

The existing 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 exceptional matrix of reinforcement for the shoes proved impossible. The solution was 'to fit these in wherever we could', says Wake. 'We contacted Austria so that they could change the shoe design to fit the bolt holes.'

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