A test for composites
ACTON Town's bridge D65A has been undergoing stress tests to research and measure the benefits of carbon fibre composites. The project is part of the DETR-funded LINK partnering programme which includes LUL, DML Composites, DERA, Structural Statics Ltd, Southampton University and MSL Engineering.
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| Partners: pictured above are those taking part in the Acton Town bridge project. From left to right, Kevin Jones, Concrete Repairs Ltd; Steve Smith, DML; Phil Webster, LU Site Inspector; Mark Wilkins, Structural Statics Ltd; John Campbell, LU Project Manager; Alan Kenchington, Structural Statistics; Cathy Wei, Dr Phil Irving and Steve James from Cranfield University; Dr Roger Davidson, AEA Technology; Dr Paul Hill, DML |
In late March, standard strain gauges as well as newly-designed fibre optic gauges (developed by AEA Technology and Cranfield University) were installed along two of the bridge's beams. These send data measuring the stress from trains crossing the bridge via a phone link to the partners.
In mid-April, carbon fibre composites were installed on the beams. Monitoring continued for an additional three weeks to accurately compare stress readings before and after. The results will be available in late May.
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| Stuck in: work done on the vent shaft at Shadwell by DML included the Resin Infusion under Flexible Tooling (RIFT) process. Adhesives are infused through the layers of carbon fibres to strengthen the structure. The process has been patented by DML |
John Campbell, LUL Project Manager, says: “We are hoping for a 25 per cent reduction in stress levels. We want to see if composites are a viable quick-fix solution. They could be used as a method to save replacement and extend the life of the asset by 20 years.”
Carbon fibre composites are not new. However they have been used mainly in the maritime industry. DML has used them extensively for repairs to Royal Navy ships where working space and time for repairs are at a premium – much like on the Underground.
In fact, DML has completed three strengthening projects for LUL using carbon fibres, including beams on Covered Ways 12 and 58, a bridge at Surrey Quays that was over-stressed and struts in a vent shaft at Shadwell.
Dr Paul Hill, Technical Manager at DML, says: “The structures on the Underground are unique, quite old and subject to a great deal of stress. Replacing them can be costly and time-consuming. Composites offer many advantages compared to traditional materials, including low density, high mechanical properties, flexibility and durability, while increasing or restoring load capacity.”
All the work is done with adhesives and no welding. This means the composites can be installed quickly, which fits within the timeframes of the Underground's engineering hours and avoids safety issues associated with hotworks.
Steven Smith, DML Project Manager, adds: “LUL has been a strong champion of composites, whereas for other companies and industries it's still seen as a novel approach. Hopefully the LINK programme will change that.”
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