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Heavier Cleddau Bridge passes storm test

CLEDDAU BRIDGE at Milford Haven last week came through the first major test of its tuned mass damper since recent strengthening and resurfacing work to its steel box girder structure.

Storm force gusts up to 125km/h buffeted the bridge whose dynamic properties have changed since a £4M programme of column head strengthening, transverse web stiffening and resurfacing (NCE 23 October).

The bridge closed from 9.30am to 6pm last Friday because the gusts were causing a traffic hazard, said bridge owner Pembrokeshire County Council's senior engineer Darren Thomas.

'This is the first big storm to hit since the strengthening was finished and the extra weight of new surfacing was added, ' he said 'But there was no sign of any excessive movement, no indication of any problems at all.'

Cleddau Bridge became notorious in 1970, when it was the first of the new generation of lightweight steel box girder structures to collapse during erection.

Its 213m main span was reconstructed with a suspended centre section housing one of the first tuned mass dampers (TMDs) to be fitted to a road bridge in the UK (NCE 28 November 1974).

This was intended to minimise wind induced deck movement when the very exposed slender, lightweight structure was hit by Atlantic gales.

Four Koni hydraulic dampers fitted to the TMD have also been refurbished and refitted.

Structural engineer Flint & Neill is anxious to verify that the TMD is still effective.

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