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Flexible friend

Engineers replacing a worn out bridge in Lancashire are calling on an innovative concrete arch structure.
NCE reports

The Construction by Lancashire County Council of the county’s first FlexiArch flat pack modular arch bridge system is currently underway in Burscough, Lancashire.

The new structure is needed to replace the existing Flax Lane Bridge which council engineers have ruled unsafe for traffic. It was closed to vehicles in April 2010 and then to all traffic, including pedestrians, in June.
Installation of the 6.8m wide road bridge began earlier this month onto pre-prepared springing blocks and foundations.

Six elements

The FlexiArch system consists of 6 arch ring elements, each of 1m width, composed of 23 tapered pre-cast blocks linked on their upper surface by a cast in flexible membrane which allows the arch ring strip to fall into its desired self supporting arch shape as it is lifted from the flat bed HGV transporter. The system is completed by the provision of two pre-cast spandrel walls.

The system was developed by Northern Ireland firm Macrete. It allows a conventional arch to be built without expensive temporary support.

The bridge in Burscough spans 8.3m and crosses a fast moving water course which has the capability to swell significantly following heavy rainfall.

Distinct advantage

Avoiding placing works in the river channel was therefore a distinct advantage.
Consideration has been made by the designers for protected species and other mammal access along the water course.

Following installation of the arch rings, the bridge arch will be back filled with in-situ concrete, the spandrel walls will be brick faced, brickwork parapets constructed and the carriageway works completed.

The scheme is being constructed and managed by Lancashire County Commercial Group along with Lancashire County Council’s Area South Design Team. The road is expected to be re-opened in June 2011.

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