35mm Long Footbridge with Conical, Radial and Elliptical Profiles

thumb_picture1In 2001 Intaspan completed the construction of a 35m long steel plate girder footbridge to span the River Lea on the Mossops Park development at Enfield. The footbridge, designed by Whitby Bird for the London Borough of Enfield, consists of a combination of conical, radial and eliptical profiles weighing 20 tonnes. Intaspan’s role was to manufacture and erect the bridge of foundations and approach ramps constructed by the main contractors Allenbuild.

The project was made particularly difficult by the very restricted access. It was impossible to place the craneage at the erection site, so an alternative method had to be devised. This was acheived by placing a 200 tonne capacity crane a distance of about 100m from the final site. Two support towers were mounted onto barges and the bridge span lowered onto the towers and towed up to the erection site. It was necessary to carefully position the bridge span over the bearings and then lower it into position by sinking the barges in a controlled operation, using 2" pumps which sank the span at a rate of 1000mm every 15 minutes. The rate of sinkage had to be carefully monitored to prevent the barges from grounding.

The bridge is an unusual design, rather like a cigar in elevation with an overall camber and like a butterfly in cross section. A free draining aluminium decking forms the light-weight wallking surface and stainless steel perforated panels form the parapets where the structure becomes very shallow.

Tha manufacturing process took 12 weeks with erection operations completed in just one day to minimise disruption to river traffic.