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Wind code blows the whistle on wobbly bridges


COSTLY WIND tunnel tests will be a thing of the past for routine bridge design, with the launch of the latest wind code, experts claimed last week.

Aerodynamic profiles of bridges can be assessed by the new BD49/01, via a simple sequence of calculations from basic data, which shows any danger of excitation, members of the Wind Engineering Society told a packed Godfrey Mitchell Theatre at the ICE.

Architect-designed footbridges, bowstring, suspended and cable stayed structures will not be covered by the guide.

'The new code is only applicable to standard bridges, but will provide designers with a tool to quickly and cheaply assess whether their structure has an aerodynamic problem, ' said Highways Agency quality services engineer Ron Ko.

Imperial College visiting professor Tom Wyatt warned that, when assessing the wind's angle of impact, taking a time averaged value is potentially unsafe.

'If the bridge has a flutter type growth rate, then resonance can be reached very quickly in some structures.' Where a gentle response is inherent, a time averaged value would be appropriate.

Wyatt later questioned the stability of UK viaducts. 'Those which have slender supports may satisfy vertical load and wind conditions, but the lateral resistance might need to be measured over several - rather than single - spans between good horizontal supports. There are many that need looking at in this country.'

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