North Dene Footbridge carries a public footpath over six lanes of the A1 near the Angel of the North in Gateshead, Tyne and Wear. Our routine inspections had identified corrosion to reinforcement within the three main steel/concrete composite spans which presented a potential risk from spalling concrete falling onto live traffic on this very busy section of the network.
We carried out a concrete inspection and testing survey to find the cause and extent of the defects which we used to develop five scheme options ranging from insitu repair of the existing decks to full replacement of the structure.
Working together with our footbridge manufacturer, our design team devised an economical solution to replace the three main spans and one shorter access ramp of the existing bridge with new steel members. This option re-used the existing piers and abutments with minimal modifications.
The new main spans were designed to current cycle bridge standards, in this case slightly wider with a higher parapet to protect users from excessive wind. Bicycle wheeling channels were also added to the existing stepped access ramp to allow cyclists to more easily push their bikes up and down. This improved access for cyclists helps the local authority develop improved routes for cyclists in the surrounding area.
The reduced construction depth of the new steel main spans also allowed for an increase in headroom clearance over the carriageways beneath, bringing this up to the current standard for a new footbridge.
Images showing structure prior to demolition and installation
Through careful planning; dismantling and removal of the four existing spans was completed in just one overnight closure of the A1 by a specialist demolition contractor on our supply chain. This required the use of two cranes simultaneously, one on each carriageway, to avoid the need to de-rig and reposition a crane part way through the process. The sections of bridge were lifted out and transported to a recycling plant in whole sections to save time and reduce noise and disruption on site.
The new footbridge members were fabricated at Nusteel Structures Ltd specialist fabrication works in Kent and delivered to site with a full protective paint system and anti-slip surfacing ready-applied, leaving minimal finishing work to be completed on site. Again, all four spans were lifted into position in just one overnight closure.
By replacing one of the access ramps, in addition to the three main spans, temporary propping of this member was avoided which further reduced disruption to traffic.
All preparatory work, including some minor repairs to the existing structure, was carried out either from off the carriageway or during overnight lane closures with no delays to traffic. Nearby residents were kept informed of all stages of the work by letter. Specific working methods were selected which reduced noise levels to a minimum and any noisier operations were programmed to be completed before 11.00pm.
By working closely with specialist suppliers, local authorities and residents we managed to deliver a cost-effective solution to address the issues presented by a rapidly deteriorating structure whilst minimising disruption to road users. North Dene footbridge continues to provide a safe crossing point over the A1 for pedestrians and now also offers better access for cyclists and opportunities to expand the local cycleway network.
Watch the timelapse of the demolition and installation here: