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Toil painting

Maintenance Forth Bridge

Painting the Forth Bridge is a euphemism for an endless job. But a contract to apply offshore techniques to the structure should change that.

Diarmaid Fleming reports.

Sisyphus in Greek mythology was condemned by the gods to an eternity of toil in the underworld by pushing a rock up a hill, only for it to roll back down. He would then have to push it up again. In modern days, if Sisyphus and the Greek gods were around, he might have found himself working on the Forth Bridge with a paintbrush.

Painting the Forth Bridge has become a vernacular for neverending work. But Balfour Beatty and Network Rail are setting out to defy the gods of engineering.

Like all good myths, there is an element of untruth. Painting the Forth Rail Bridge from start to finish only to begin again immediately on reaching the other end has never really happened, says Network Rail project manager Ian Heigh.

'Back in the old British Rail days, there were always people working on it. A dedicated crew worked full-time on maintenance on the bridge, but there are parts of the bridge which have not been painted in a long time because of the Health & Safety at Work Act, which made access to some areas impossible, ' says Heigh.

But from the bridge's opening in 1890 until current safety standards came into play, its painters have used some unconventional and dangerous methods. In the last century, sometimes fortified with beer or malt, painters performed deathdefying gymnastics while often climbing the bare steel itself.

Some sat on plank seats tied to ropes tethered from the structure, while others used rope ladders and bosun's chairs until the practice was outlawed by the Health & Safety at Work Act in 1974 (NCE 8 March 1990).

Heigh says that lack of paint on the inaccessible spots did not affect the performance of the structure, but that the need to avoid Sisyphean maintenance promoted them to begin looking in the mid-1990s at a way to do one major job which would last.

'Structurally, the bridge has never been in danger. Before we worked on a 'need to do' basis and began developing a database of which parts of the bridge needed to be painted. Trying to do the whole bridge came to be considered as a possibility then, ' says Heigh.

The old paint applied over the years ranges from coats of leadbased paint to alkyd systems.

'We want to remove all of that back to a blasted surface, onto which we apply a zinc phosphate primer, then a glass flake epoxy paint coat with a top coat of acrylic urethane, ' Heigh explains.

A detailed programme of testing of the steelwork was needed to see what the paint was to stick to. 'We took samples dotted about the bridge, 150mm by 50mm plates and did elongation and shear tests. Because of the simplicity of the process when the steel was made, there is little variation and it is good quality, equivalent to modern Grade 50D.

Preparation of the steelwork is critical for the project. Painting onto a surface with impurities will lead to problems later on.

Although the structure is in good condition, the opportunity is being taken to carry out any repairs to the steelwork provided by probably biggest paint-stripping job in the world.

McGregor Energy Services is doing this work, while Palmers and Pyeroy have subcontracts for gritblasting and painting.

After blasting back to the steelwork, the primer must be applied rapidly. In the windy marine environment 'gingering', or light rusting, takes place within four hours. 'If you miss it, you have to go back and flash-blast to remove the gingering, ' Heigh adds. Paint must be applied within seven days, with application only after the primer has been subject to a cleandown and a detailed inspection.

Getting the paint right is one thing, but getting to paint at all is the biggest challenge on the job.

'The actual painting is the easy bit. The logistics and access are the hard parts, ' says Balfour Beatty Civil Engineering (BBCEL) project manager Malcolm Hyatt.

Stepping out onto the bridge is a stomach-churning experience for anyone even slightly wary of heights. From the main access walkway below the railway line the difficulties faced by the site team become clear. Scaffolding on the project has been erected by SGB and Palmers, with abseilers nonchalantly twirling 100m or more above sea level.

Erected sections cling like ivy to parts of the structure, and are covered in Shrinkwrap - a robust plastic which wraps like clingfilm around the scaffold sections. 'We are trying to create a factory environment - and encapsulation helps us protect the environment, ' says Hyatt.

'It can take three months to put an access system in place for painting which takes only two or three weeks. The Shrinkwrap is used to provide containment when the old paint is removed. After gritblasting, it is simply sucked up by large vacuum cleaners, ' adds BBCEL sub-agent John McArthur.

Aluminium scaffold tubing is used on some sections to save weight. Dead loads from the scaffold and live wind loads from the sheeting are significant and are checked for impact on the bridge by Network Rail's consultant Pell Frischmann.

Getting the scaffolding and materials to site has been another huge challenge with different solutions required. On the Fife side, land access to one of the bridge's masonry caissons has enabled hoists to be installed, but landing platforms have had to be built at caissons in the middle of the Forth to allow materials be brought by barge. Some parts of the bridge can only be supplied by rail during possessions.

The weather has a major impact on the works. Even on a mild day, the wind can be sharply felt high up on the bridge. Condensation forms on steel at 0infinityC, so painting cannot take place in cold weather, but it is the wind which causes the greatest difficulties.

'The weather is the biggest problem. As a general rule, when the wind speed is above 40mph (64km/h) we cannot work on the bridge, and risk assessments have told us that in some areas we cannot work when it is over 20mph (32km/h), ' says Hyatt.

'But the length and size of the bridge means there are different microclimates, so when it's too windy to work in one place we can often do work elsewhere.'

Safety is paramount: the project has won a regional safety award and has had no threeday reportable injuries to date.

The works also have to contend with over 180 train movements a day on the bridge, adding to the complexity of the task.

The contract awarded in 2002 is to an RT24 'emerging cost' form, which pays the contractor for the work done. This has been in operation for two years. A target-cost, open-book contract will be negotiated when BBCEL and Network Rail have some experience under their belts and greater certainty about what is involved. The work, which involves an estimated 20,000m 2of painting, is likely to cost around £10M a year and will continue until 31 March 2009.

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