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Helix bridge lifted over M8

The main span of a new £5.1M, 90m long footbridge weighing 230t was lifted across the M8 in Scotland last week by the biggest mobile crane available in the UK.

The motorway was closed at 8.30pm last Friday and the bridge was in place by 9pm. The motorway was reopened to traffic at around 3.00am on Saturday, some three hours earlier than planned.

"We have been on the project for many months now," said Raynesway Construction project manager Graham MacAlpine, "and it all went like clockwork."

The 1200t mobile crane with 600t super lift was brought on site last Tuesday and took two and a half days to assemble. More than 45 articulated lorries were used to deliver the crane components to site.

The footbridge is a distinctive helical truss design with a 70m main span, designed by Buro Happold.

"There are 12 tubes which wind round the structure in a criss cross effect. Inside there are straight tubes top and bottom which form the chords," said Buro Happold associate director Simon Fryer.

"It’s like a normal truss but the bracings are formed by the helix. It’s complicated geometrically."

The bridge replaces an existing footbridge which was built to serve the first motorway service station in Scotland in 1965. This bridge is now in a poor condition and lacks wheelchair access.
The new bridge also serves a park and ride scheme.

"What we’re trying to do is develop the interchange," said Transport Scotland deputy project director for construction Graham Porteous.

"We’re trying to get people out of their cars. People will be using the bridge to get across from the carpark on the south side to the bus interchange."

The M8 is the busiest motorway in Scotland carrying 51,000 vehicles daily.

Before the lift, the structure was assembled at ground level and lifted into position fully glazed and painted. Polycarbonate glazing was used as it is low maintenance. A maintenance walkway sits on the roof.

"The whole thing was geared round minimising disruption," said Fryer. "It was lifted with all bits fitted on.

"So many people will see it –most people in Scotland will know it. It’s an unusual and eyecatching design on a very busy road."

Watch the bridge lift at www.nce.co.uk/video

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