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Wheel of fortune

When the Queen officially opens the Falkirk Wheel in May, she will be acknowledging not just completion of the world's first revolving boatlift, and the final link in Britain's most ambitious canal restoration project, but also the creation of a corridor of commercial opportunity stretching coast to coast across Scotland's central belt.

David Hayward charts a construction project completed in half the time originally planned; explains a piece of canal machinery more tourist attraction than boatlift, and analyses why the Millennium Link Canal is even more important for what develops beside it than travels along its waters.

Early next month the first of an expected 200,000 visitors a year will converge on a former tar works site near Falkirk to ride on Britain's most unusual tourist attraction. Their 45 minute journey, in futuristic style amphibious vehicles, through canal tunnel, along high columned aqueduct and then dropping spectacularly 25m off its end within the world's only revolving boatlift, will be the highlight of their day out at Scotland's latest leisure park.

Most visitors will leave knowing a bit more about canals and the strange looking boatlift that gave them such a novel white knuckle ride. Few though will realise they have experienced a watershed in engineering technology; a moving sculpture designed equally by engineers and architects and set to become a 21st century construction icon.

Even fewer will be aware that the Falkirk Wheel, soon to number the Queen among its early visitors, is not the one originally tendered three years ago. And they would be fascinated to learn that today's eye catching version needed a hastily assembled Lego model to convince the client of its economic simplicity.

'It is now more tourist attraction than boatlift, ' claims George Ballinger, chief civil engineer for that client, British Waterways Scotland.

This central connection at Falkirk between the Millennium Link's two different height canals was always to be the project's focal point. Some form of lift was needed to transfer boats from the upper Union Canal to the Forth & Clyde 35m beneath.

But the original 1999 tendered design for a Victorian style ferris wheel, with hanging gondolas, was abandoned when it was realised that no one really liked it. What emerged from the unprecedented brainstorming session that followed could not have been more different (see page VI) The new version performs the same role but has as many artistic descriptions and architectural interpretations as people asked. Yet whether it is a spine and rib cage, a Viking longboat or a working sculpture concealing proven 20th century engineering within futuristic imagery, to steelwork designer and fabricator Butterley Engineering it was, a year ago, more a complex jigsaw of 30 major wheel sections occupying most of its Derbyshire factory.

'The wheel is a clever illusion, ' says Butterley director Colin Castledine. 'But it is essentially a series of conventional engineering functions brought together in a unique way.'

Butterley's £5M subcontract to main joint venture contractor Morrison-Bachy Soletanche, included erection of the wheel as well as design and fabrication.

So a decision to pre-assemble sections on its factory floor was to pay dividends later on site.

The large Meccano-like collection of massive 12 piece curved box beam arms, three part axle and multi section gondolas had generally bolted rather than welded connections. This was a consequence not mainly of the need for preassembly, but more the structure's unusual loading forces during operation.

As the arms rotate, lifting or lowering some 400t of gondola and water, they repeatedly face 100% stress reversals, with sections changing from total tension to total compression.

'Fatigue on the continually moving structure is high, with the weight of the gondolas always a live load, ' explains Castledine. 'Bolted connections can weather this fatigue stress better than welds.'

The hassle of matching all 15,000 bolts with an incredible 45,000 bolt holes - vividly described in punched out steel terms as over 7t of holes - was counteracted by much easier assembly both in the factory and on site at Falkirk to where the 35 lorry loads of parts were delivered last summer.

Here a 1,000t Demag crane, hired for a week to complete wheel erection in five separate lifts, was paid off a day early.

Positioning 270t sections, to a 10mm tolerance, was completed virtually trouble free, thanks to the prematching operation. With the entire wheel temporarily suspended on an adjustable falsework stillage, mating the axle with the aqueduct was achieved to 1mm accuracy.

Follow-on commissioning work demonstrated that the macro engineering of a 13,000t rotating wheel carrying 500t of water in its gondolas, still faced the challenges of micro engineering when minute particles of grit in hydraulic rams threatened progress. As the rotating gondolas arrive at either the end of the aqueduct or the docking bay in the lower basin, their flap gates must mate exactly with similar units on the fixed structures.

The 200mm gap between the two gates is then enclosed by a flexible rubber seal allowing this short infil section to be flooded and the gates lowered. It was the rams operating the gates that had been contaminated with grit forcing all 10 cylinders to be stripped down and reassembled.

The computer controlled wheel is designed to turn near continuously, completing its half revolution operation every 15 minutes. Maintaining the same weight of water in the two gondolas is crucial, so a £600,000 automated network of sensors, transducers, valves and sluices ensures that water levels in the upper aqueduct and lower basin remain within 37.5mm of the correct computed levels.

Sophisticated software constantly monitors this entire water regime and, if levels are likely to exceed safety margins, an automatic cutout prevents the wheel from turning.

'The last thing we want to do is stop the wheel, ' explains Morrison-Bachy Soletanche project manager Jim Steele. 'So we use an intelligent computer system able to predict and self correct water levels.'

But the wheel is not the only 'wow generating' factor on site.

The first of a £1M fleet of four state of the art amphibious vehicles arrives soon to add even more originality to the £6.50 ride.

The 45 minute journey, first on road and then through canal tunnel, along aqueduct and over the wheel will all take place in the same vehicle. Fully adapted for road use, this 'boat with wheels' should, says the park's general manager Iain Herbert, be ideal for corporate use with guests collected from their hotel, driven to site and into the water without moving from their seats.

Herbert is keen to stress that boat owners wishing to use the wheel for its original - though now somewhat secondary - purpose of transferring between canals, will not be forgotten. Traditional narrow boats will share gondolas with their 21st century counterparts - a sight no doubt adding to visitor appeal.

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