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Wheel of fortune

When the Queen officially opened the Falkirk Wheel in May, she was 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.

The first of an expected 200,000 visitors a year is starting to 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 a 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, which will 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.

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 ú5M ($7.2M) subcontract to main joint venture contractor Morrison - Bachy Soletanche, included erection of the wheel as well as design and fabrication. So a decision to preassemble 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 $869,000 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 $1.4M fleet of four state of the art amphibious vehicles arrives soon to add even more originality to the $9.40 ride.

But the park's general manager Iain 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.

Trade routes

The world's first coast to coast ship canal, the 57km long Forth & Clyde, was completed by John Smeaton in 1790 allowing cargoes ranging from Highland whisky to Baltic timber direct access between the Atlantic and the North Sea.

Sailing ships negotiated 32 opening or swing bridges, 40 locks and 25 aqueducts journeying between ports at Bowling, Glasgow and Grangemouth.

By contrast the unusual 51km 'contour' Union Canal, which opened 32 years later, boasted 62 masonry arch bridges and 24 aqueducts, but no locks at all. Its engineer Hugh Baird followed - to an accuracy of 25mm - the now 73.14m contour level providing a route for coal barges from central collieries direct to Edinburgh. The two canals were later linked at Falkirk, where an 11 lock staircase overcame the 35m height difference.

Both waterways were unceremoniously closed in the early 1960s when road engineers first opted to save a few thousand pounds by routing the A80 at low level over the Forth & Clyde and, a few years later, cut just $23,000 of their construction bill by severing the Union Canal with the M8 motorway.

Millennium momentum

A 'sold out' sign signals the success of half built flats at Edinburgh's new 'Canalside' development - a site that, until last year, had not seen a canal for 40 years. And, across the country at Kirkintilloch near Glasgow, a town until recently boasting only a blocked canal basin of rubbish strewn stagnant water, a newly erected roadside sign proclaims it 'Scotland's Canal Capital'.

These are but the advance guard of an expected $580M worth of wide ranging business developments attracted to the Millennium Link - a coast to coast network of the refurbished Forth & Clyde and Union Canals now in full flow again after near half a century of neglect and abuse. 'And I am optimistic our forecast of creating 4,000 new jobs will be exceeded.' says director of British Waterways Scotland, civil engineer Jim Stirling.

Stirling's wry smile conceals the years of frustration as he lobbied for finance. A decade ago, thoughts of reopening stretches of BWs onetime prime asset were the dreams of narrowboat enthusiasts only.

But, by the time Stirling's team had worked up a $148M plan to remove over 30 obstructions, and rebuild or replace 120 structures, the tide was starting to turn.

Such projects were being seen by BW, and its government master, as transforming rundown areas into corridors of opportunity. But matching such ideals with the cash to create them still faced traditional challenges.

The project's potential main funder, the Millennium Commission, initially rejected the scheme as too costly, so Stirling's team value engineered its construction, pushing into later phases extensive dredging. A revised $113M plan did the trick, though by the time the $46M Millennium Commission grant was confirmed, the deadline had passed for expected European Union match funding and BW had to wait for the next round.

By February 1999 - three years late - Stirling finally had all the cheques he needed and transferred the worry beads to his chief civil engineer George Ballinger with orders to complete in two years a construction project programmed for five. No time extension was possible as most funding came dependent on the original spring 2001 completion date.

The canal network had boasted 100 bridges, 49 aqueducts and 40 locks. Yet there was little along the 110km route that did not now need either restoring, rebuilding or unearthing. Locks leaked heavily, and most of the Union Canal's 62 masonry arch bridges needed major refurbishment as did the aqueducts. Virtually all the Forth & Clyde's 32 swing or lift bridges had been replaced by infill road embankments with canal water culverted through.

Near where the two canals converged at Falkirk, a boatlift would span the 35m vertical height difference to provide a novel link, replacing the original flight of 11 locks now buried beneath roads.

But Ballinger's plan to let only a few contracts at a time working linearly through the network, was scrapped in favour of the big bang - awarding virtually all 25 in one go.

Losing three years of planned construction played havoc with programming. 'If just one contract was delayed so was the entire link, ' recalls Ballinger. 'Some sections only just made it.'

The two refurbished canals, still awaiting their Falkirk Wheel central link, were reopened on schedule last year and Stirling confesses to being 'stunned' at their early success as a catalyst.

'If all this was about just restoring canals, we would have wasted $113M, ' he claims. 'It is much more about the social and commercial regeneration of an area blighted by high unemployment.'

Cog control

Whether engineers call the wheel a moving structure or a piece of canal machinery, all are agreed that the really clever bit is a row of five differing sized cogs hidden behind the arm nearest the aqueduct.

The prime challenge in changing from free hanging gondolas - as on the original ferris wheel - to fixed units supported each end within the propeller shaped arms, was simply keeping them horizontal.

As the arms rotate, the wheeled gondolas try to remain level by running against a single curved rail track fixed to the rim of the hole in the arm supporting it. But wheel friction, and the inertia triggered by 250t of disturbed water, would result in the gondola sticking and tilting.

It is estimated that, after just 40 seconds, the resulting 4infinity tilt could cause the gondola to tip over totally. The row of cogs, between axle and gondolas, now prevents this possibility by keeping both troughs horizontal throughout the arms' rotation.

The wheel is perfectly balanced and its axle can be turned by 10, 7kw geared motors located around it for a cost of just $14 a day. As the wheel rotates, two small cogs on each arm turn against a stationary larger cog fixed to the aqueduct pier behind the axle.

These small cogs also connect with two outer cogs, the same diameter as the central one and located in each arm's gondola support hole. Outer cogs, and the gondolas rigidly fixed to them, always rotate at the same speed as the turning wheel - effectively keeping the gondolas horizontal.

This simple yet innovative mechanism, devised by RMJM architect Tony Kettle, had to be demonstrated to the client and funders. So he modelled the cog arrangement with Lego 'borrowed' from his eight year old daughter Sarah, quickly proving the technique's effectiveness.

'Sarah was impressed that I could assemble something without instructions, ' says the architect.

Butterley's Colin Castledine, a civil engineer, admits it was a 'brilliant idea', but adds with a smile: 'The gear ratios on his model were all wrong and the gondolas would still have turned over.'

Flood setback

Although the official opening wil still go ahead, operation of the wheel has been delayed due to damage caused by vandalism.

The wheel's sensitive electronic and hydraulic equipment was flooded when vandals smashed through padlocked lockgates, releasing over 80M litres of canal water to cascade on to the structure.

Project team

Client: British Waterways Scotland

Main contractor: MorrisonBachy Soletanche JV

Structural consultant: Arup

Architect: RMJM

Wheel subcontract: Butterley Engineering

Civils consultant: Tony Gee & Partners

Mechanical consultant: Bennett Associates

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