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Station masterpiece

Atkins | 18 Sep 2015 | Comments

Technical excellence, flexibility and a collaborative approach were all crucial requirements for the Atkins design team as they engineered the award-winning Birmingham New Street Station.

Like any epic journey, turning Birmingham’s 1960s reinforced concrete railway station into a futuristic transport hub, would be full of twists and turns. “We were running four design programmes in parallel, all at different stages and each affecting the building and that was quite complex,” says Stephen Ashton, Atkins’ engineering director on the £750 million project.

Birmingham’s 1960s reinforced concrete railway station
Birmingham’s 1960s reinforced concrete railway station.

Starting in February 2008 Atkins’ original contract was for detailed design of the station redevelopment for client Network Rail. This would open up the dark and gloomy underground platform complex and increase passenger capacity in the station through the creation of a new concourse, improve vertical access to the platforms which sit below ground level, and deliver an enlarged station building. All of which was to be enveloped in an iconic futuristic roof structure.

“On day one we hit the first major challenge. Following a review by the Department of Transport of the GRIP 4 design it was agreed to implement some changes to improve and enhance the concourse layout and so we were instructed to redesign a significant proportion of the scheme,” explains Ashton. Changes to the layout including a new eastern entrance were requested and so Atkins got started on this, as well as progressing the original detailed design contract in order to ensure that the client and principal contractor Mace could keep the project on schedule. As these first two design streams got underway the team carefully watched to ensure that any changes to the outline design were incorporated into the detailed design workstream.

A few months later in September the architectural contract for the façade and roof structure was awarded to Foreign Office Architects (FOA). A third design stream then commenced as the team worked to move this section of the project through early design stages. However from the outset it was clear that the chosen design would have a major impact on the work that had already been undertaken. “The FOA design changed the concept in that the original façade and roof design consisted of a glazed frame with its own foundations but the new structure used stainless steel cladding that hung off the existing building,” says Ashton.

The glass roof had been replaced with a transparent polymer called ETFE (Ethylene Tetrafluoroethylene) which was to sit on 30m long structural steel arched trusses
The glass roof had been replaced with a transparent polymer called ETFE (Ethylene Tetrafluoroethylene) which was to sit on 30m long structural steel arched trusses.

The glass roof had been replaced with a transparent polymer called ETFE (Ethylene Tetrafluoroethylene) which was to sit on 30m long structural steel arched trusses. “We had this whole new loading system coming into the building with new roof structure and cladding combined with the removal of the central part of the existing reinforced concrete frame. This means we are changing how the building moves, how loads were being applied and therefore we needed to analyse the building to ensure that the end product was stable,” said Ashton. From this the Global Stability Analysis (GSA) tool was born.

This digital model enabled the team to mimic the impact of local design changes across the whole structure, running computational analysis as major changes were made. Ashton says that throughout the project there were six key construction stages where the model was used as a construction tool to ensure stability through the build and advise on temporary works design. In the case of the new roof the team sought to ensure that loading was carried vertically through the existing reinforced concrete columns. “As a result of all these loading changes we ended up strengthening 52 columns with concrete jackets of 100-200mm thick depending on the loads,” says Ashton.

Commercial impacts

If things were not complex enough commercial considerations then threw another bump in the road when in 2010 Birmingham City Council negotiated an exciting deal to bring John Lewis into the Pallasades shopping centre above the station. News that the company would open its biggest store outside London at 250,000 sq feet was announced in February 2011.
“Once the negotiations had concluded and John Lewis agreed to come to Birmingham, Network Rail added in the south side development and that was the addition of the new building along with the redevelopment of the Pallasades shopping centre, which is now Grand Central,” explains Ashton.

The fourth major design programme was born and once again it had huge implications for the design of the station redevelopment. The new steel framed building appears to step in to the existing structure at the southern end where the careful and piecemeal demolition of the existing 22 storey Stephenson Tower made space for it. Some of the existing structure at roof level also had to be taken out allowing the new structure to expand over the top of the station like a mushroom. However there were still limits on how much load the existing concrete structure would be able to absorb from the new steel frame.

“What you don’t want to do is to add stresses in the existing structure by causing any deflections in the concrete beams and columns as the new structure and foundations settle with the load. What we have had to do is design a jacking system that was installed between the new steel columns and existing concrete beams along with a deflection monitoring system. The jacks are adjusted so that there is controlled deflection of the existing structure and hence no change in its loading,” says Ashton.

He explains that the connection between the new steel framed structure and the existing concrete beams needed bearings too, to account for the load induced movements, such as thermal movements, of concrete and steel structures. “We designed the bearing and the movement system for the joints to make it so that you don’t know these are two different buildings. We also designed the foundations to the John Lewis building to a very tight settlement criteria such that the settlement that occurs from the loading was minimised. We didn’t want the new building settling significantly compared to the existing building,” says Ashton.

Design of the various elements then continued to progress at different rates so integration was a project buzzword. Ashton says that having senior members of the engineering team leading the coordination efforts was critical as each took responsibility for their discipline: “We ran a separate team on the John Lewis building so in some areas we had two drawings per area which we then had to integrate such that we only had one set.” With over 3,500 drawings prepared as part of the detailed design and another 500 for the John Lewis building the task was enormous.

Quick changes

Even more challenging was that as contractors started onsite it became apparent that the limited available as-built drawings did not accurately reflect the true condition of the building. “We had requested intrusive surveys for the start of the detailed design but the client was not able to undertake a significant number of these because it would mean closing parts of the station and Pallasades Shopping Centre which could not be done. So the decision was made to undertake those intrusive surveys during construction,” says Ashton.

This meant making a lot of design assumptions about the existing building from the size of columns to percentage of reinforcement. Although the team made conservative estimates to be sure of the structural integrity they also assumed that the building was in relatively good condition which unfortunately turned out not to be the case. In some areas poor construction work on the 1960s building meant that the concrete contained a lot of voids, various concrete elements had deteriorated and rebar became exposed. Original movement joints for the building were not where the plans said they were.

“Contractors were onsite telling us that the building was not like the drawings, so we were forever going out to site to validate or update our drawings,” says Ashton. But the clock was ticking. Phase one opening for the first half of the new concourse was set for April 2013 and with full phase two opening in September 2015, Atkins quickly brought in more resources to ensure that work could progress. “Our design team for the construction stage flexed in size in response to the project demands with a peak of 180 during phase one,” says Ashton.

This kind of fluctuation in staff numbers happened several times throughout the scheme and Ashton estimates that over 800 design staff have worked at Birmingham New Street since work began in 2008. Critical to this flexibility was the work of engineers in the Atkins Global Design Centre in Bangalore, India. “They have done a really good job in supporting us,” he says, but points out that it was a group effort with Atkins’ offices from all over the UK contributing.

The GDC team was ramped up as the work progressed and with program being the key focus, a dedicated team of architects, engineers and technicians worked relentlessly ensuring that high quality designs were delivered.

“The key for successful delivery from the GDC was the engagement with the client and contractors. Design team leads interacted with the client representatives, project managers from MACE and various suppliers located in the UK and other parts of the world,” explains Raja Narwari, Atkins’ GDC practice manager for Rail Solutions. “This allowed the design teams to fully coordinate the designs and give a thorough consideration of buildability.”

With so many changes cropping up, Ashton confirms that having a good relationship with the contractor was vital especially as changes had to be made during the construction phase. “It wasn’t an alliance in contractual terms but we have worked collaboratively to come up with the best solution possible while protecting the design. We wanted to help make the construction as easy as possible whilst assuring the integrity of the structure,” says Ashton.

Ashton continued: “Looking back this has been a fantastic journey during which the Atkins team has applied fundamental engineering principles, knowledge and experience to enable the transformation of this extraordinary building – a structure made up of nine interdependent concrete frames over eight levels, a final concourse footprint five times larger than Euston station along with the addition of the steel framed JLP building over four levels and 187 M&E systems to be commissioned.”

And what a structure it is. Birmingham finally has a gateway that befits its status as the UK’s second largest city and what is more the improved accessibility with four entrances rather than two, is opening up the southern part of the city. “This station will draw more people to Birmingham and lead to regeneration of the southern part of the city. It will have a big impact on those who live and breathe Birmingham,” says Ashton.

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