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Hyder Special Structures project manager on Hammersmith Bridge.

Hammersmith Bridge may be seven decades older than the Tamar Bridge near Plymouth, but it has taught Simon James a few lessons that came in useful while designing the refurbishment of the latter.

'I've learned an awful lot about construction sequencing and traffic management,' he says. 'Now I look at Tamar with a fresh pair of eyes.'

Project manager on Hammersmith since June last year, James has doubled up as joint project manager for the detailed design of the strengthening and widening works on Tamar for the last five months. Hammersmith is due to re-open in September 1999, by which time work should have begun on the Tamar project.

Although he has worked on several historic bridges, James acknowledges that Hammersmith is something special. He waxes lyrical about the structure's innovative suspension chains, usually assumed to be wrought iron like most of the 110 year old structure.

'In fact they are very early examples of structural steel. They are made up of alternate interlocking eight and nine leaf links - and the thickness of leaves in the eight element links is increased proportionately to keep cross- sectional area constant throughout.'

This week work starts on the trickiest part of the historic structure's latest refurbishment - the replacement of seized roller bearings on the bridge's northern tower.

What Hyder is planning for the Tamar Bridge is a much more ambitious operation.

Faced with the need to strengthen the bridge to take 40t trucks and increase its capacity while keeping at least three lanes of traffic open, Hyder opted to add extra lanes cantilevered outside the line of the existing suspension cables. These would be supplemented with extra cables: not, as in the case of the 25 April bridge in Lisbon, with extra suspension cables, but with straight cable stays.

'In fact my first involvement with the project was nearly three years ago, when I helped optimise the cable stay locations,' James says. 'We believe it is the first time in the world that a classic suspension bridge has been strengthened in this way.'

With two lanes of traffic diverted on to the cantilevers, the existing composite deck will be removed 'in longitudinal slices' and replaced with an orthotropic steel deck.

'This won't be my first such deck,' James reveals. 'I've just spent six years as project manager on a telescope in Hawaii - which has a similar deck as its lowest floor'.

Since joining Hyder in 1990, James has been something of a bridge specialist. Telescopes apart, he has helped assess the Britannia Bridge in Anglesey and a rail bridge over the River Exe, as well as being involved in the detailed design of a major viaduct on the A13. Even his one venture into buildings featured a cable stayed factory structure in Germany.

Things were different during his two years with Whitby & Bird, where James was mainly involved in building refurbishment in London. Before that, however, his eight years with Sir Owen Williams & Partners were marked by several bridge projects - though none as complex as Tamar or as politically sensitive as Hammersmith.

'Tamar is a landmark structure, a very impressive sight, ' James concludes. 'But Hammersmith is beautiful - even if it isn't very big.'

Dave Parker

(see feature p34)

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