Precis of "Design & Monitoring of the Flintshire Bridge, UK"
published in Structural Engineering International, Vol.3, 1999by Peter Curran and Graham Tilly, Gifford & Partners.
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Precis of "Design & Monitoring of the Flintshire Bridge, UK"published in Structural Engineering International, Vol.3, 1999by Peter Curran and Graham Tilly, Gifford & Partners. |
This paper describes the design and monitoring of the Deeside Road link cable stayed bridge, undertaken by Gifford and Partners, which was installed and completed in 1998 (see attached figure). Instrumentation was included during construction to aid the management of the bridge both during construction and during its service life. One of the particular interests was the performance of the cables and anchorages, as there had been problems with similar designs due to rain/wind induced vibrations. Accelerometers were fitted to eight of the cables to monitor their performance. In addition load cells were fitted to several of the cables aimed at providing information about traffic on the bridge and fatigue loading on the anchorages. Several corrosion sensors were also included in post tensioned ducts, and in the splash zone, because of previous concerns about corrosion in tendons.
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Aerial view of the Dee Bridge. |
As part of the overall monitoring a load testing programme was undertaken, using vibrating wire strain gauges, in selected areas of the bridge. A static load test was carried out using eight 32 tonne aggregate lorries at pre-determined positions along the length of the bridge. Deck and tower deflections, stay loads, and strains in several components were monitored. Predicted responses were made beforehand, and compared with measured responses. In most cases the agreement was very good, (e.g. actual tower deflection 85% of predicted, deck deflection 90% of predicted. Only in the case of strains in several transverse beams was the agreement less good, with an increase by a factor of 2.34 on the predicted strain being measured. This was partly due to restraints imposed by the main longitudinal beams, which were not fully modelled. Overall these results provided a very useful confirmation of the design calculations.
When the paper was published there had been no instances of vibration in the cables due to combinations of wind and rain. However long term monitoring will confirm whether the damping system introduced has been fully effective.
Corrosion monitoring is recognised as a long term activity. It is hoped that the sensors will provide early warning of any electro-chemical activity before real corrosion develops.
Overall the inclusion of instrumentation in the bridge is providing the ability to manage the bridge more efficiently in inclement weather, and from long term monitoring any deterioration of the bridge, before major repairs are required.
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Guage in transverse beam. |
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Load test in progress. |