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HOW IT'S HANGING

Roped access techniques were considered the least disruptive way of refurbishing hangers on the Tamar bridge. Ed Owen reports.

When it was built, the Tamar road bridge had the longest central span of any suspension bridge in the country, with a 335m main span, since overtaken by the first Severn bridge and the Forth and Humber bridges.

To comply with European Union rules and to add capacity and life to the structure between 1999 and 2001, it became the first major suspension bridge in the world to be strengthened and widened at the same time.

As a key structure on the highway network it is vital that the bridge is well maintained, cleaned and repainted regularly. The bridge carries up to 50,000 vehicles per day so there are inevitably constraints on lane closures for maintenance.

Cornwall County Council, acting for bridge operator Tamar Bridge and Torpoint Ferry Joint Committee, brought in the services of TRAC to clean and re-paint the hangers. TRAC's General Manager, Bill Wintrip is project manager on the job.

"The Tamar bridge hangers – the vertical cables that carry loads from the vehicle deck up to the main cables – are spaced every 9.1m across the bridge. In total there are 120 hangers, varying in length from 2m to 32m, each 54mm in diameter," he says.

"A survey in 2006 confirmed that repainting would be required to preserve the hangers."

Rope access allows a team of up to seven workers full access to the hangers and work can take place with only one lane of traffic closed. "The majority of our work will be carried out by the use of industrial rope access (abseiling), where we will descend down the hanger cables from the main cable," says Wintrip.

As with any work at height, safety is critical, "The work requires specific safety measures to contain our painting activities and all tools, paint and equipment are attached with lanyards," he says.

"The high level work is undertaken off-peak with some lane closures. Close liaison between the TRAC painting team and the Tamar Bridge Team is essential to monitor weather and traffic conditions and to ensure the safety of the operation and minimise traffic disruption."

When abseiling, to keep hands free for the painting, the teams work in pairs, one lowering the other to work on the hanger cable.

"There is a particular method for applying the paint – you can brush it, but as the hanger diameter is thin enough to get your hand around, we first clean the hanger to remove any contamination, then we use a sheepskin mitt to apply the paint. This way the painter can work the paint into the wire strands."

The paint is itself unusual. "It is a viscous metal-rich paint that does not set hard. Although it becomes dry to the touch it remains highly flexible and allows the hangers to flex without cracking the paint."

TRAC provides rope access services throughout the UK. "We have just finished work on the QEII Bridge to change all the gantry rail bolts. Similar painting work to the Tamar project is carried out on masts and towers.

"Some masts can be 350m tall, and we often apply the same type of paint to the masts' wire stays," says Wintrip.

The Tamar job began in late April, and will be complete in six weeks.

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