Rail Industry Focus

A toast rack of ribs

As RTM was being printed, the final rib of Manchester Victoria’s grand new roof was due to be lifted into place. We caught up with project manager Jed Hulme of Severfield, the Bolton-based company that is one of the biggest structural steel businesses in Europe, just after the ninth and biggest of the 15 ribs had been installed – a major milestone in the £44m redevelopment of Manchester Victoria.

“It was a successful lift,” Jed Hulme tells us. “We’d been preparing for this lift for six or seven weeks, and we were all geared up and ready to go.”

Hulme is project manager for steel company Severfield, which has been installing the ribs to support the stunning £16m new roof at Manchester Victoria. The ribs have been installed during short 3.5-hour overnight possessions, because the OLE used for the Manchester Metrolink light rail system has to be isolated.

When RTM talked to Hulme, every rib had been installed within that possession window with no late handbacks. “There was no reason for us to think this one, Rib 9, would be any different – but we were primed because it was the biggest rib of the 15.”

The ribs (each 1.2m deep and 500mm wide) are far too big to be delivered in one piece – Rib 9, for example,  was delivered in five pieces, each an average of 20m long and weighing 20 tonnes. The rib sections were transported from Severfield’s Bolton factory into Manchester city centre by Eddie Stobart and JB Rawcliffe & Sons Ltd, before being manoeuvred onto the site through a 4m wide gate.

Hulme said: “We bring them to site in separate modules, and we build what we call a level jig, level with the floor on site, high enough off the floor so the guys can get underneath to weld the ribs.”

Welding and the ‘toast rack’

Sections A and B were welded together, then C, D and E, to form two ‘units’.

Hulme explained: “Once those were welded, and everything’s been tested and painted, we then lifted each section up into what we call the ‘toast rack’, which is a pre-formed jig structure that stands at the side of the flat jigs.”

Each unit is lifted into position, to form the rib as it will eventually be in situ, then the two units are welded together to form the final rib.

This was all done in the 10 days before the possession, followed by blasting, priming and painting of the rib connections to make it ready for the final lift.

That occurred on the morning of 3 August, using a 750-tonne LR 1750 crawler crane. The team had previously been using a 1,200-tonne LTM 11200 telescopic crane from Mammoets, the UK’s largest.

Hulme explained: “The LR 1750 crane we used for Rib 9 has got a 56-metre main boom and a 56-metre buffing jib, which makes it more versatile for us to stretch out to a possible 92-metre radius, and we can actually move the crane because it’s tracked. So, when we pick something up, we can move it into position before it then leans out to put the rib into place.”

The strops were attached to the rib, the crane located in its correct position, and then the rib was lifted out of the toast rack while the team ensured everything was balanced correctly and in the right position.

“Then it’s a waiting game,” Hulme said. “We were in the hands of Network Rail and MRDL, the Metrolink operators. As soon as they gave us the green flag, we were allowed to slew around.”

The new roof doesn’t actually touch the existing building – the ribs are supported by ground-level buttresses and a column, from which they cantilever to the building. This avoids putting excess loads onto the existing historic structure.

Rib 9, because of its length, has two columns and two pinned connections. “Ribs 1-8 have only one pinned connection, so there was an extra operation involved in this one,” Hulme said. “The rest had been cantilevering over the middle column. This one, because the cantilever was over 30m, had to have another column at the end. This will happen on Rib 10 and Rib 11 as well.”

The team dropped the rib down onto the second column, pinned it off, then dropped down onto the base to locate the Macalloy bars into the concrete buttress.

Hulme explained: “We then had to tie the girder off with two tying purlins at strategic points – our designer Mick Slack tells us where we have to put them – so we’ve got some stability within the structure as soon as we release the big crane.

“When we’ve got the crane ready, and once everything’s been tied off, and everything’s secure, we release the strops from the rib and then slew the crane back, and then hand back to Network Rail.”

Before the next rib could be installed, more stability purlins had to be installed within the structure, between Ribs 8 and 9.

Finishing the job

Following the successful Rib 9 lift – “an incredible achievement for us”, Hulme said – the final six ribs start descending in size again. Rib 10 and Rib 11 were both done in one weekend – August 9 and 10 – taking advantage of the fact that the Arena was closed for bi-annual maintenance. That lift involved a 500-tonne crane located outside the station, lifting items over the existing roof, while the big crane in the car park was used to lift Rib 10 into place.

The final four ribs were done weekly, until the last one was finished on 7 September. Hulme expects the Severfield team to be on site for another two to three weeks doing final infill purlins and gable steelwork frame, plus bolting-up checks and painting.

Severfield is supplying and erecting about 1,900 tonnes of structural steelwork for the project – not just the roof ribs, but also the mezzanine floor to link the station to the Arena, as well as lifts and a ‘feature staircase’.

The team has been using ‘4D’ construction sequence models to ensure the deliveries are precisely planned and tracked, as the logistics and site management aspects have been among the most challenging parts of the job.

Asked how challenging the Manchester Victoria roof structure has been compared to previous jobs he has worked on, Hulme told us: “It’s pretty much business as usual – in that we don’t do ‘usual’ structures. We do the structures no-one else wants to do. The last job I worked on was the Orbit structure at the side of the Olympic stadium. Up to this one, that’s been the most fascinating job I’ve ever worked on.”

The roof

Work has also now begun to install the roof’s 21,500 sq m of ETFE (ethylene tetrafluoroethylene) panels: a lighter, cheaper, self-cleaning alternative to glass, as used at Manchester Piccadilly and Birmingham New Street stations and the Eden Project in Cornwall. Vector Foiltec is the contractor for those works.

The whole project is due for completion in early 2015. The main contractor is Morgan Sindall, with BDP Architects. Hyder Consulting are the structural engineers.

Ian Joslin, area director for Network Rail, said: “The new concourse will be lighter, brighter and more modern than the old one and will complement the original station building’s beautifully restored architecture. When it opens next year, Manchester Victoria will be a station of which the city can be proud of.”

Hoisting and positioning

The precise choreography of the hoist and positioning were achieved using Severfield’s own 3D laser technology, which allows for the pinpoint alignment of complex connections so that structures fit to tight tolerances.

Boxes are made up of four pieces of plate section nested and cut to their unique profile and assembled as an open lid box, welded fully inside then closed with top plate and welded on the outside. Once fully welded to the correct shape, Severfield sets all the connections to tight tolerances. To achieve this, it employed its own leading-edge shop assembly method, developed over the last decade, that employs 3D models and laser technology, shooting xyz coordinates to the bolt holes, which in turn provide a confident fit-up on site.

Source: Severfield

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