By the 1880s, railway engineers in the UK had really got the bit between their teeth when it came to steel bridges. Up until then, it was the stone masons and the brickies who had ruled the roost with structures that have lasted to the present day and which will likely last for another century or two (with maintenance).
Up until then, metal bridges had been limited by the materials available and, to a large extent, by the vision of the engineers of the time. But come the 1880s – or at least the latter part – larger, chunkier structures were replacing the somewhat-too-flexible bridges that were beginning to show their limitations under heavier loadings.
The locomotive engineers, too, were flexing their muscles. Larger loads, larger locomotives. The bridges just had to keep up. When new lines were built in the back end of the nineteenth century, these too were on a bolder and chunkier scale. Nothing seemed to be impossible, so when the Chester Northgate to Hawarden Bridge Junction line needed to cross the River Dee, then this was just another obstacle to conquer. Construct a 165 metre long bridge with provision for all the tall trading vessels as well? Not a problem. The engineers just got on with it with a massive structure and a massive opening portion that swung majestically under steam power.
The Hawarden bridge was opened in 1889 after a two year construction period. The 85 metre opening span, designed by C.A.Hobson, allowed shipping to pass upriver to Chester and was at the time the largest such bridge in the UK. Weighing 764 (metric) tonnes, it could swing through 90° within 40 seconds.
Past its prime
But the world moves on. The tall ships to Chester stopped going to Chester – or anywhere else for that matter – and the bridge swung for the last time in 1960. The steam houses with their boilers have been demolished. The winches and chains remain as visible reminders of a splendid achievement. The bridge is fixed. Despite its name, the Hawarden swing bridge….. doesn’t.
There are a number of other things the bridge doesn’t do – or at least didn’t do before the major works that were carried out by AMCO Rail and Network Rail over the past two years.
For example, it didn’t allow trains with an axle load of greater than RA7 to pass over at more then 20mph and then only with one track loaded.
Although hardly on the seaside, Hawarden – and Shotton on the other side of the River Dee – are harsh estuarial and industrial environments.
The weather and seawater has not been kind to the bridge and so structural repairs as well as strengthening was required.
Network Rail’s aim was for the bridge to be strengthened so that it had an RA10 rating.
An extra three months
AMCO Rail was engaged to carry out the works with design partner Cass Hayward. An initial design required extensive additional steelwork to the soffit of the structure. This prompted a re-think and so sampling and testing of the steel within the existing bridge was commissioned.
Analysis proved that the existing steel was of sufficient strength to enable the majority of the soffit steel to be removed from the design. This successful challenge to standard analysis was critically important due to limitations on clearance and the Grade II listed status of the bridge.
Once the final design was complete, AMCO Rail was contracted to grit blast and paint, strengthen and carry out other general repairs to the structure.
AMCO Rail, along with AMCO Engineering (another part of the AMCO group) and Jack Tighes, an experienced grit blasting and painting contractor, then planned and executed works. Works started in Sept 13 with an initial 46 week program.
Early in the planning stages the analysis of the structure revealed that the bridge did not have sufficient capacity to carry full ‘traditional’ steel scaffolding. As a result all the scaffolding used was aluminium.
Even then, the works were carried out in two phases due to the capacity of the bridge.
There were further limitations on the works. Freight traffic was reduced to 5mph and two trains were not permitted on the bridge at the same time. Scaffolding was erected in stages so that strengthening to the top boom could take place before the soffit scaffold could be erected allowing the soffit to be grit blasted and painted. But as Tony McCann, Amco’s site agent, wryly observes from his years of experience: “You don’t know what damage you’ve got until you get the old paint system off!”
And indeed, following blasting it was established that a significant amount of condition-led repairs were required. In the end, these extended the contract by another three months.
Once the repairs and strengthening systems had been finalised, the work progressed much as any other grit blast and paint project. The weather was varied, of course, but because of the encapsulation system used, most of the site was protected. That’s not to say that working conditions weren’t challenging on occasions. Because of the tight structural clearances between the scaffolding and the running lines, working space could be somewhat cramped.
At first, access appeared to be a problem. Servicing the works from one end only with a massive 500kva generator some distance from the bridge prompted a thought to occur to Tony. Right by the bridge was a derelict building on Tata Steel’s land. This was down for demolition but, with appropriate words and inducements arranged by Network Rail land agents, Tata rewired and replumbed the building after which Amco made the place habitable for the duration of the contract. This, along with an area of land made available for plant, ensured a smoother operation.
Span 10 – the navigation span posed its own unique problems. Airbus A380 wings, which are manufactured at nearby Broughton, travel under Hawarden Bridge on barges around three times a week, on their way to Mostyn harbour where they are loaded onto a custom-built roll- on, roll-off ferry for the trip to France.
A cradle system, which could be pulled back to Pier 10, was developed to allow passage of this ultra-high- tech equipment under the vintage infrastructure. Under a protocol agreed with the Harbour Master and Afon Dyfrowy, the cradle was docked one hour prior to the passage of a wing.
Statistics of success
The official opening day (of the project, not the swing span) was on 12 November last year by which time the following statistics could be presented:
£8 million scheme (£4 million painting, £2.5 million strengthening and £1.5 million condition-led)
- Over 85,000 man-hours worked on the project;
- Only one, no-lost-time, minor accident;
- No RIDDORs;
- No environmental issues;
- Over 550 tonnes of grit used on the structure;
- Over 7,000 litres of paint applied to the structure;
- Over 12,000 tension control bolts used;
- Over 130 tonnes of additional steel on the structure.
Most importantly, the project objectives had been met. There has been the complete removal of operational restrictions. At just 25mph, it’s not a high-speed railway – but the bridge now has a full RA10 rating. Those engineers of the 1880s would have been proud of their descendant’ achievements. Sure, the bridge doesn’t swing, but that’s because of changing trading patterns. It still stands as a proud monument to what engineers can achieve.
There’s an unexpected twist in the tale. That building? The one that was to have been dropped by Tata? It’s had a new lease of life. As part of the Gateway Project, an ambitious Council-led scheme to provide thousands of new homes and new businesses in the area, a contractor has been appointed to install two kilometres of sheet piling along the river to provide flood protection.
They’ve found ready-made accommodation!