Footbridges are simple structures, and so is installing them. A few concrete pads, two steel lattice towers – prefabricated off-site, a couple of staircases, and a steel bridge deck that can be lifted into place overnight while the railway is closed.
Simple – and quick.
Except…bridges now have to be accessible to wheelchairs, young children in buggies and heavy luggage on wheels.
No problem – just replace the two staircases by gently sloping ramps.
Except…a footbridge deck is typically 6.5 metres above the ground. With a 1:12 gradient, the steepest allowed, that means the ramps have to be 78 metres long. Even folding them back on themselves and its still around 40 metres long. That’s a lot of space that’s needed.
OK then, so go for lifts instead.
That solution means concrete lift shafts, winding gear or hydraulic rams, a substantial electrical supply, pits under the lift shafts, fail-safe control gear, 24/7 monitored help line and still quite a bit of space.
Suddenly, it’s not as simple as it seemed.
And what if there is no space – even for a simple footbridge?
A case in point is the project to build a footbridge, on High Street in Lincoln, to provide pedestrians with an alternative route across the railway other than the existing level crossing. 35,000 pedestrians and cyclists use the crossing every day, and so do over 140 trains.
People are often seen running over the crossing once the lights sequence has begun, and even when the barriers have started to lower. CCTV footage taken from January this year shows a woman fall as she attempts to run over the crossing before the barriers close.
This misuse has resulted in the crossing being rated as number one on the level crossing risk register for the London North Eastern and East Midlands route, and one of the top five most dangerous crossings in the UK.
Network Rail therefore contracted Galliford Try to build a footbridge, complete with a lift at each end, to give pedestrians a safer alternative when the crossing gates were shut.
The first challenge was – where to put it? With buildings on both side of the road on the northern side of the railway, there was no obvious place.
Enter the lateral thinkers from Network Rail. If the buildings are in the way, then buy one of them and knock it down.
So that was what happened. Network Rail bought the former Sleep Shop building on the east side of the road and demolished the front third of it. This gave room for the bridge – the other side of the tracks was conveniently vacant next to a multi-story car park.
Commencing June 2015, the front bay of the three-storey building was demolished to create space for one of the abutments. During the process, asbestos was discovered on the concrete roof structure under the bitumen coating. At first, the team from Galliford Try attempted a scraping technique to remove the asbestos but, within hours, ceased the operation as air tests showed that safe working limits were being approached.
Following consultation with the Health & Safety Executive (HSE), an alternative technique was employed. The roof beams that contained the asbestos, each weighing 25 tonnes, were encapsulated in a glue-like liquid and plaster of Paris wrap and then lifted out by a 250-tonne road crane during an overnight road closure and nine-hour overnight rail possession last December. The beams were too large to remove directly from site for disposal, so were cut into two within an encapsulation tent.
Thereafter, a remote-controlled Brokk robot was used to demolish the front of the building, working from the third floor down. Brokks are ideal for demolition in confined spaces, and the use of larger plant was also unviable because of the close proximity of the site to the railway line. The contractors could not risk disturbing the track or allowing any debris to fall onto it.
With the site cleared, construction of the bridge towers could begin.
Well, almost. On investigation, the site was found to be riddled with services – 57 operational cables for signals, power, telecoms, points, heating and so on that needed to be relocated before work could begin.
Once the site was finally clear, piling for the tower foundations could start. Forty 273mm piles were driven down to a depth of eight metres, topped off with hefty concrete ground beams to support the structures. Lift pits were dug, 2.5 metres deep, and lined with concrete.
The steelwork for the two towers was lifted in during three Saturday night possessions from late January, as was the 21-metre lattice-girder bridge deck which had been manufactured in Doncaster by Carver Engineering Services. Once the steel steps were also in place, the towers were clad, using the bracket and rail cladding system, in weather boarding, Kingspan insulation board and then, after all of the cabling had been fitted, a final layer of Shackerley composite stone cladding.
Stannah lifts and associated hydraulics were installed in April, as were the glazed balustrading and handrail.
All of the concrete pouring and crane lifts had to take place during Saturday night possessions for safety. The cladding and the glazing of the balustrade, however, could be carried out in normal working hours.
The glazed balustrade is unusual. City planners didn’t want the bridge to look too imposing, so the glass was specified to give it a light, almost invisible, appearance.
Safety was so high on the agenda at High Street that the bridge was opened as soon as it was safe to do so, even before it was completely finished. Three weeks of late-night closures were required after the actual opening, during which the lifts were also brought into service.
“The bridge has been a challenging but satisfying project to undertake,” commented Wes McKee, rail director at Galliford Try, “because of the amount of night work and the complexities of getting plant and materials, particularly the steel bridge sections, to site in such a busy, central location.”
Rob McIntosh, route managing director for Network Rail, added: “Safety on the railway is our absolute priority and building a footbridge on this scale, in such a heavily used and built up area, has presented lots of challenges, but we have never wavered in our commitment to deliver this footbridge and separate pedestrians and cyclists from trains at High Street level crossing. What we need now is for people to use it, to make it part of their daily routine, and not take a chance by running over the crossing when the barriers are closing.”
But what of the part-demolished building that still stands alongside the new bridge? Network Rail has now received planning approval to demolish the remainder of 179 High Street and replace it with student accommodation in conjunction with joint venture blocwork LLP. As part of this development, a pedestrian route will be provided through Wigford Yard, better connecting the University campus and its new faculty building with this part of High Street. blocwork is a joint venture between Network Rail and bloc, established to maximise value from under-used property assets next to the railway. Generation of profits by the partnership will help contribute to the upkeep and renewal of the rail network.
Be that as it may, Lincoln now has a shiny new footbridge to keep its pedestrians safe and away from any temptation to take a gamble with their lives, which must be a job well done.