Sometimes only made-to-measure will do. Just ask the project team that’s been exercising its logistical dexterity for the past six months to resolve the failings of a landmark Yorkshire bridge. Time and tide have been overcome, bringing operational benefits to the network and a loo for the signaller who perches on top of it.
The 18th and 19th centuries saw many commercial vessels ply their trade on the River Ouse. Although the opening of the Aire & Calder Navigation in 1826 greatly reduced traffic levels, tall sailing craft still had to be accommodated when the North Eastern Railway came to engineer a crossing of the river, just east of Goole, for its line linking Gilberdyke with Thorne Junction.
Designed by Thomas Harrison, its five 116-foot fixed spans were erected by Butler & Pitts of Leeds whilst Newcastle firm W G Armstrong & Co constructed Span 2 across the navigation channel – a swing span of 250 feet, driven by hydraulics. By the time of its opening in 1869, similar technology had been deployed on many movable rail bridges but this one was reputedly the second largest on the planet.
As built, the swinging span comprised three hogback wrought-iron plate girders, 16 feet 6 inches at their deepest point. Its pier was formed of six cast-iron cylinders arranged in a circle, each 90 feet from top to bottom and sunk about 29 feet below the river bed. A seventh column at their centre acted as the pivot for the bridge’s rotation. The span’s entire weight of 670 tonnes was borne by a ring of conical live rollers. Opening and closing it took just 50 seconds and relied upon an accumulator storing the power needed to work the hydraulics. This was charged by a 12 horsepower steam engine.
Whilst the success of the engineering was undeniable, the structure occasionally succumbed to forces beyond its control. In 1973, Pier 3 was effectively lost and its adjacent spans damaged when a craft collided with them. Significant remedial works were required. And 17 years later, the Upside girder of Span 3 had to be replaced after a vessel pushed it off its bearings.
More recently, the inadequate strength of the bridge and its deteriorating condition – specifically, corrosion in the web of the main girders and their connections to the transverse beams – have driven the imposition of speed restrictions: 60mph for passenger traffic and 30mph for freight, with RA9/10 limited to just 10mph. Operational flexibility has also suffered through a prohibition that precludes trains passing on the structure. Network Rail recognised the need to tackle these constraints and engaged Pell Frischmann to undertake the three-year design lead-in for the bridge’s first major refurbishment.
Since the Sixties, permanent telecom feeds for the signal box above Span 2 have dropped down from cables slung across the water between two masts. Signalling indications came via disengagers at the ends of the swing span, meaning they were lost when the bridge opened. Facilities for the signallers were basic – with no mains supply, bottled water had to be delivered. Calls of nature involved a walk off the end of the bridge.
Pipeline specialist Clancy Docwra Ltd was awarded a services upgrade contract in June 2009 and spent the following autumn installing ducts beneath the river bed – one from bank to bank carrying signalling, telecoms and FTN (Fixed Telecom Network) cables, and two more to provide the mid-river jetty with fresh and foul water pipes as well as electricity and S&T cabling. The latter will overcome intermittent reliability issues with the disengagers. A highly accurate GPS system ensured the drilling equipment surfaced at precisely the right place, avoiding timber piles that have remained in the river since the bridge’s construction.
Preparatory works for the refurbishment got underway following the appointment of Carillion Civil Engineering as principal contractor last March. These would culminate in an intensive six-week blockade starting on 2nd October. Recognising that every new piece of steelwork – all 400 tonnes of it – would have to fit first time, four designers from Pell Frischmann were immediately mobilised to fully dimension the bridge, right down to each rivet centre. That process took three weeks.
The compound accommodating Carillion’s project team alongside site management colleagues from Network Rail was established through the latter half of June, after which Lyndon Scaffolding began to wrap a platform and encapsulation around the fixed spans. Once this was complete, grit blasters and painters came in to start work on the main girders’ outer face and underside of the transverse beams. Span 2 wasn’t touched as ‘Rules of the Route’ possessions did not provide sufficient time to erect scaffolding, confirm it was safe and ensure the bridge could still swing.
Darryl White, Network Rail’s Scheme Project Manager, explained that the principle behind the strengthening design was to create a U-frame action, stiffening the bridge to maximise the compressive stresses allowed in the main girders. Three basic elements were involved – diagonal plan bracing between the transverse beams and main girders, additional web plates on the main girders towards the ends of each span where the existing web was under-strength, and full-height stiffeners to transfer the load from the top flange – also under-strength – to the transverse beams. Fitting 400 stiffeners was deemed the lesser of two evils – the alternative being to take out every rivet from the top flange and then over-plate it. All this steelwork, each piece individually measured and designed, was fabricated by BritCon Ltd and arrived pre-painted.
The blockade programme encompassed almost 700 items, all meticulously sequenced. A multitude of “little things” brought great complexity as every action was interlinked with others. Some of the web plates had a cut-out to accommodate transverse beams – these had to go in before the stiffeners which could only be installed after the p-way had been relaid as they were to be transported by roadrailers. The stiffeners incorporated a gusset plate to carry the new walkways which in turn supported lever arm mounts for the rodding that pulls the disengagers apart. You get the idea.
Some fluidity was brought to the programme by river traffic. Closing the waterway was not an option as shipping enjoys a right of way. On average, at least one vessel passed through daily, costing about 1½ hours in work time on the swing span. During the three weeks it remained open, a crane barge from Alan Oliver Work Boats ferried materials to and fro, mooring in the eastern channel. Outgoing craft – of which there was less notice than those heading upstream – passed on the western side of the jetty. When the span was closed, a radio message providing an hour’s warning of a vessel’s approach triggered a procedure to clear everyone off the swing span and then open it before confirming to the pilots that the channel was clear. No chances were taken, even though this generally took just 20 minutes.
Prior to the refurbishment, the track was carried on waybeams with direct cast-iron fastenings. Issues had developed with both vertical and horizontal alignment as well as significant wear to the rail ends where the swing and fixed spans met. Considerable effort was made to minimise the gap there. To ensure the new rails could only expand in the direction of breather switches beyond the bridge and on the swing span, a series of back-to-back components fixed them rigidly to the structure. Amongst these were two Pandrol Vanguard units to hold the rail in its correct position and reduce vibration, and a pair of rail locking mounts – fabricated steel pieces bolted through the web.
More problematic was expansion of the bridge itself which runs east-west. A temperature difference of 20C can arise between the north and south-side girders, especially in the winter. Very occasionally, this has produced sufficient distortion to jam the swing span. For six months, expansion detection systems and heat monitors were set up to provide some indication of how temperature and movement were correlated. According to John Billcliffe, Carillion’s Construction Manager, this data helped the team to optimise the gaps at both ends of the swing span when the rail was cut. A four-coat winter paint system was applied, with Pearl Grey (‘white’ effectively) chosen as the top coat’s colour to reflect heat and minimise thermal expansion.
The design for the new rail bearer beams identified the position of every hole for the specially-developed guide rail mount – which was navigated through the approvals process in just three months – and 1,600 Pandrol Vipa units. These make use of resilient rail pad technology to attenuate vibrations which would otherwise be transferred to the supporting structure.
Once on site and fitted with their hardware, the bearers for the western spans were lifted onto the end of the bridge by a 250-tonne Mammoet crane, located in the corner of the compound. They were then hauled into place by means of a winch block sitting on the abutment and a pulley system at the end of Span 3. Slip plates on the transverse beams and a temporary ‘ski end’ bolted to the bearer prevented any snagging. This was an onerous process, taking a couple of hours each time. For spans 1 and 2, a Monster Bug from Hydrex was used to transport the bearers from a crane delivery point on the approach embankment to the abutment where another winch system took over.
Concrete transition ramps were installed off the ends of the bridge, above which are breather switches and collector rails to gather in any derailed vehicle. Once the p-way work was concluded, fitting of the stiffeners could get underway. For the fixed spans, BritCon had developed a lifting mechanism using a beam, sitting on the top flange, and a block and tackle. At upwards of 400kg, the size of the swing span’s stiffeners precluded this approach, instead requiring the use of RRVs.
More to come
The full tale of this project is one that’s hard to tell, such are the number and depth of its challenges. I’ve not even touched the hydraulic system’s knuckle rams, pipework and cut-off valves that have had to be bagged, removed or renewed. The team involved has not felt obliged to think inside the box, for which it must be commended. Many benefits have accrued consequentially.
And it’s not over yet. Although the blockade was lifted on 13th November, non-critical bolting is still being completed and finishing touches applied to the paintwork. The signal box will soon be liberated from its GRP cladding and dressed more appropriately; there are handrails and a new walkway to install; services await connection to bring relief to the signaller. Spring will be with us again by the time the cable masts are down, the scaffolding dismantled and the compound demobbed.
At a time when the industry is rightly coming alive to the advantages of standard modular components, here is a scheme that had to embrace ‘bespoke’. But painstaking planning and dedicated contractors have brought the project in for a respectable £6 million. And what’s been delivered has a long-lasting tailored fit.