I have changed trains at Birmingham New Street station more times than I care to remember, moving from one platform to another alongside up to 200,000 other passengers who use this busy station every day, and I have a confession to make.

Usually, I manage to negotiate the platform change without too much difficulty but my confession is that, on arrival at my destination platform, I become totally confused and disorientated. The points of the compass seem to dissolve in my head and I haven’t a clue from which direction my next train will be coming. So, reader, you will appreciate that writing an article about the enormously complex and very impressive changes that are currently taking place within and around the station has been a personal challenge. I even got confused about where the new atrium roof is situated but please do read on.

Unfortunately for Birmingham, its main line station does not have a good reputation with the travelling public. The existing station complex is made up of nine separate buildings including a car park, shopping centre formerly known as the Pallasades and office accommodation. It is dark, overcrowded and no longer fit for purpose with dingy underground platforms overarched by a 1960’s concrete structure that forms the concourse and the extensive shopping centre above. The station complex also acts as a barrier, dissecting the city centre with no recognised routes through, thus creating a north-south divide diametrically opposed to the national picture with the north side of the city being affluent and the south lagging behind. But this is all changing.

Seven-year programme

The £750 million scheme (around £600 million for the station build and a further £150 million for the re- branded Grand Central shopping centre and John Lewis above) to transform the station and the surrounding area is a seven year programme that started in 2008. The vision for such radical change was instigated by a collaboration of interested parties. The Birmingham New Street redevelopment project is being delivered by Network Rail and is funded by Network Rail, Birmingham City Council, the Department for Business Innovation and Skills, Centro and the Department for Transport. It is the city council’s view that radical development of the station complex will revolutionise neglected parts of the city with the potential to generate £2 billion into the local economy.

However, Network Rail is the station operator and so has the responsibility to coordinate the project and act as the developer for the works. At the outset, it was decided to bring in Mace as delivery partner. Chris Montgomery, Network Rail’s project director, explained that Mace brings a level of expertise in disciplines that Network Rail is not so familiar with, such as large-scale cladding and the construction of the atrium structure – skills that are clear to see when considering Mace’s most recent undertaking, the construction of the Shard alongside London Bridge station.

Following two years of design and planning, work started on site at Birmingham New Street in January 2010. The programme of work includes five station entrances and more public space both inside and outside the station.

At present there are only two entrances to the station. These new entrances will offer access through the station complex throughout the year, opening up access to all the surrounding areas and significantly reducing the north-south divide that currently exists.

Plastic bubble roof

All twelve station platforms are being de-cluttered and refurbished with new lifts and escalators. Additional space is being created for a new concourse area which, on completion, will be five times larger than the original station concourse. Much of this work is well under way but probably the most dramatic development to date is the creation of a transparent ethylene tetrafluoroethylene (ETFE) plastic bubble roof supported on curved tubular steel trusses which was completed in September and designed to bring more light to the new concourse area.

ETFE is the material used on the Eden Project in Cornwall, the outside of Bayern Munich’s Allianz Arena, and the Beijing National Aquatics Centre. It is also the material being used for the new station roof at Manchester Victoria station currently under construction.

Higher technical level

Completing the atrium structure and covering it in ETFE is the culmination of six years’ work and is without doubt a significant milestone.

To create the space necessary for the construction of the atrium and the concourse, Network Rail purchased two floors of a car park located at the front of the old station main entrance, spanning over the station platforms. One of the floors was demolished and the newly acquired space was used to equip the first part of the new station which opened in April 2013. As Chris pointed out, this was not a simple task and was certainly a challenge for the demolition contractors, Coleman & Company, which, he added, has done an excellent job in taking demolition to a higher technical level and demonstrating the skills necessary for today’s world.

Clearly, Coleman & Company had prepared carefully for the next challenge – demolishing 6,000 tonnes of concrete under the new atrium roof. Working together with JCB, they produced a “Mega Muncher” machine with hydraulic jaws which could reduce large concrete beams into rubble in a quick and effective manner whilst keeping noise levels down to an acceptable level and leaving the surrounding key structural columns in good order.

More than 4,000 tonnes of concrete has been removed so far using the Mega Muncher, with a further 2,000 tonnes to go to create the cathedral-like atrium which will form the centre piece of both the station and Grand Central shopping centre above.

Creating space

Demolishing the inner frame of the 1960’s concrete structure has created space for the new Atrium Concourse. The engineering challenge throughout this process was to avoid the structure from imploding. This was achieved by developing an understanding of how the building would behave both during and following such drastic surgery and taking the necessary steps to prevent this from happening.

This task fell to Atkins, which provided the structural analysis, led by Stephen Ashton, the engineering director for the project. He explained that the Atkins team developed a global stability model which enabled them to understand how the 1960’s structure would behave under the new loading when the work was completed. They also created a construction sequence analysis that identified five key stages of the construction programme and, with this combined information, they were able to understand exactly how the structure would behave during the various transitional phases of demolition and the changing loading.

As a result of this analysis, the beams are considered adequate for the new loading as are the foundations. However, the calculations indicated that some of the columns would need to be strengthened and so a reinforced concrete jacket was designed and constructed where required.

Flexing roof

Once they knew that the 1960’s structure was now adequate for its proposed purpose and the necessary space created for the atrium, the most dynamic part of the project – the new tubular steel and ETFE roof – could get underway. This roof is formed from two elongated domes which, in turn, transfer the roof loading onto a steel box girder perimeter beam.

Of course, roof loadings are variable due to rain, snow etc. and the roof structure will flex outward dependent on the loading. To compensate for this potential movement, which Atkins estimated could be up to 180mm, fourteen bearing plates, two of which are fixed while the others allow for some varying movement, were positioned under the perimeter ring beam before both it and the roof structure were lowered, carefully transferring the loading onto the original concrete structure. This work has now been successfully completed and the overall structure is being continually monitored for any unexpected movement.

To add another degree of complication, the new spherical roof is a different shape to the existing concrete frame. This means that, although the concrete beams that support the slab can be removed, the box girder beam cuts diagonally across the existing roof which leaves two triangular-shaped sections, one at each end of the roof. These will remain in place and their loading will have to be carried by the box-girder perimeter beams.

The solution required the development of a complex process involving a grillage of steel beams supporting temporary stressed hanger bars which were designed to support a total of eight existing concrete beams. The retained length of beam to be supported whilst they were being cut varied in length and weight from six to 17 metres long and 30 to 60 tonnes in weight. The new atrium box beam now has permanent hangers fixed to the soffit of the existing concrete structure. Once the hangers were in place, a second cut enabled the redundant concrete structure to be removed and for the loads to be effectively transferred to the perimeter ring beam.

Temporary work expertise

This temporary works solution took more than a year to plan and was successfully executed without incident. Jacking specialists Hevilifts were employed to carry out the stressing and Tony Gee & Partners undertook the temporary works design alongside the structural engineers, Atkins and AKT11.

Work is now well under way for the demolition of part of the former Pallasades, making way for the construction of the atrium which forms the centre piece of both the station and the new Grand Central shopping centre.

The demolition will also enable light to flood the new concourse from above and will eventually enable millions of passengers to appreciate the real benefits resulting from all this work – natural light!

The project delivery director for Mace, the principle contractor for the work, is Martyn Woodhouse and he is responsible for the day to day management of a diverse range of workers. On any one day there can be upward of 900 people working on the project for Watsons on the steelwork or Balfour Beatty on the platforms or Martifer on the cladding, just to name a few. In the New Year this number could extend to 2,000.

Martyn has had to deal with a sub-surface railway station with all the additional fire precautions involved. He has to cope with asbestos, working alongside an operational railway and the removal of more than 20,000 tonnes of materials. The team is very proud that nearly 98% of the materials removed from site are recycled. They are also have an excellent safety record partly, driven by a monthly 8am safety briefing to everyone present.

System commissioning

There is still a fair way to go until September 2015 when the total benefit of this work is revealed to the public. There are also 187 systems that will have to undergo a commissioning process before operational approval can be granted. However, the people of Birmingham can already appreciate the new stainless steel cladding on the outside of the emerging buildings. This cladding has been carefully angled so that it doesn’t reflect sunlight into the train drivers’ eyes at any time of the year, yet it is also angled so that the public can see the reflection of train and people movement all around them which is the underlying theme and intention devised by Foreign Office Architects.

The part that I am personally looking forward to is sitting in the new large concourse bathed in natural sunlight, waiting for the announcement of my next train which will be waiting for me when I proceed down to the appropriate platform which will be spacious, uncluttered and well lit and not at all disorientating. Now that IS something to look forward to.