PD Naidoo & Associates, Johannesburg
SOUTH AFRICAN ENGINEERS AND PROFESSIONALS SCORE ACCOLADES AND A WORLD CLASS STADIUM
The months of anticipation are nearly over and the World Cup is in sight. Preparations for the stadiums, airports and 2010 fast-tracked infrastructure are at their final stages. A collective sigh of relief can momentarily be shared before the kick-off on Friday 11 June.
Much has been said about the legacy of 2010 and its intended spin off for South Africa beyond the duration of the world's largest sporting event hosted for the first time in Africa.
Only time will reveal the extent of its benefits or drawbacks. However, what has been achieved to date on 2010 construction projects alone shows just how much can be accomplished with the right mix of skill and will.
A closer look at the stadiums built in Durban, Cape Town, Port Elizabeth and Johannesburg demonstrates this.
Kick off in Soccer City
Take Soccer City as an example. Its sheer magnitude, as Africa's largest stadium, rising 60m into the air on the outskirts of Soweto, is matched in stature by its emblematic design, a design that will be showcased to the world in the broadcast of the opening game between Bafana Bafana and Mexico City.
Conceptualised to resemble a calabash, or hollowed-out gourd used for storage in many parts of Africa, the Soccer City stadium can seat up to 89 000 spectators.
It has taken approximately 10 million man-hours, 10 000 tonnes of reinforced steel, 9 000 tonnes of structural steel and 85 000 cubic metres of concrete to achieve the final product.
Its facade is composed of laminated fibre reinforced concrete panels in traditional earthen colours and punctuated by a combination of open and glazed panels to create a patterned finish resembling that of the traditional African pot.
And like a pot, the calabash structure sits in a depression that is the "pit of fire". This demarcates the security and turnstile line dividing the outer and inner perimeters.
The polycarbonate roof is cantilevered from a triangular spatial ring truss and covered by a sand-coloured PTFE membrane. An aerial view onto the stadium reveals 10 black lines cutting through the mass of orange seats which align with vertical slots pointing to the nine other World Cup host stadiums and the Olympiastadion in Berlin, Germany, the venue for the 2006 World Cup final.
From Design to Engineering
But what did it take to turn this chosen design into the final structure?
A discussion with Hans Koorn, Director at Consulting Engineers, PD Naidoo & Associates (PDNA), who were the principal consulting structural engineers for Soccer City, reveals the complexity of the project that started in February 2007 and achieved practical completion in the second week of March 2010.
Previous FNB Stadium in Soccer City location|
New stadium being built over the old |
Says Hans, "There were so many important connection points that had to be catered for. For example, the roof was manufactured in Italy, and we appointed German engineers as our sub-consultants to do the design of the roof. So there were many different countries working on it and it was all managed from here."
The design for Soccer City was chosen by Danny Jordaan, Chief Executive of the World Cup Local Organising Committee (LOC), from a portfolio of 10 proposals conceptualised by Architect Bob van Bebber of Boogertman Urban Edge & Partners in association with Populous.
The task of taking it from design to a purpose built stadium on the site of the existing FNB pavilion rested on the engineers in collaboration with the architects and the construction team.
Says Hans, "It was a shape that the architect had defined. In retrospect it was a good choice because it looks lovely, but it was an engineering challenge."
Using the 120 sloping facade support columns as an example, Hans says, "each column is 17 metres high and the top of the column is offset by 6,5metres from its base. Because gravity always works downwards, and engineers always like things to go in the same direction as gravity, we had to make sure that those forces come down to the base. So that was a huge challenge."
Furthermore, there was the slim profile that the architects wanted, in order to achieve the right aesthetics. Because of the slender shape of the facade column, a lot of reinforcement had to be used. According to Hans, a column would normally have 200kg per cubic metre of reinforcement.
For the Soccer City columns however, 860kg per cubic metre of reinforcement was used. This meant that the standard method of compacting concrete was not an option and so it was decided to use self-compacting concrete. According to Hans, very good concrete strengths and finishes were achieved this way.
Retaining its history
The decision to retain the existing FNB site was made for historical and financial reasons, but in many ways it did make construction of the new stadium more difficult. Historically, it was too important a stadium to demolish, having been the premier venue for football matches, the location for the 1990 mass rally following Nelson Mandela's release from prison and the 1993 setting for Chris Hani's commemoration.
However the load capability of the stadium was limited and it was designed for a small, cantilevered roof. Working around these limitations meant isolating the new bowl structure from the existing one so as not to put new loads onto the pavilion.
Software to overcome Structural challenges
Hans says, "If the old stadium wasn't there we would have designed the new seating structures to take part of the roof loads and changed our philosophy accordingly. As it is, there are huge loads coming from the facade and the roof."
Laminated fibre reinforced concrete panels |
"We're talking uplift loads of 580 tonnes and downward loads of 1000 tonnes on some of the piles which go down about 33 metres and are socketed a further 6 metres into rock. Those piles are 1.5 metres in diameter."
According to Hans, every single pile position was set out with co-ordinates using the CAD module of Civil Designer, an infrastructure design package developed and supplied by Knowledge Base. PDNA also use Knowledge Base's Civil Designer software package for their civil engineering infrastructure work.
Mandy Koorn, who brought her skills and expertise to the draughting process for the Soccer City stadium, says she must have produced 3 000 drawings and issued approximately 5 000 co-ordinates in the CAD module. These included the exact position of every pile as well as the setting out data of the geometry of the stadium.
Mid construction with view of structural aspects|
"The co-ordinate system in Civil Designer's CAD module is better than any other package I have worked on", says Mandy.
On a project of this magnitude and intricacy, with for example the steel manufacturers located in Italy, and so many points of connection between concrete and steel, there is no margin for error.
"Take the facade columns for instance," continues Hans. "Because the radius and diameter increases at the same time, the columns extend further part. All these three dimensional aspects required co-ordinates."
"The facade columns and the tie beams that hold them together to prevent long term deflections, have huge forces. As the tie beams go up they get longer. Their exact position on site had to be determined using co-ordinates."
Then there are the shafts. According to Hans, there are 14 large shafts that surround the stadium, taking all the horizontal and vertical loads, with anchors or tendons that are cast deep into the shaft. All the bolt and tendon positions had to be calculated using co-ordinates.
PDNA Consulting Engineers
As the principal structural engineers on the project, PDNA were required to attend regular coordination meetings with other consultants and sub contractors. Following their appointment and the tendering process for all the subcontracts, there were regular meetings held with the international team.
As a member of the principal team, Hans and his colleagues met every Monday for a design meeting at the offices of the Architects, Boogertman Urban Edge & Partners, and every Thursday on site, over a three-year period.
Asked about the history of his involvement on similar projects Hans says, "Previously Mandy and I were with KSS Consulting Engineers where I had acted as the technical consultant for the South African Football Association (SAFA) for the 2006 and 2010 Bid. Mandy did most of the drawings for that as well. So we have had a history with the stadiums in general."
Having to choose between being on the LOC technical team or working as a consultant on the detailed design for Soccer City, Hans chose the latter. At this stage he approached PDNA about a joint venture.
Says Hans, "The initial discussions were to form a joint venture, because they could offer us a lot of resources. The joint venture talks ended up becoming merger talks. When we merged we were about one tenth of the size of PDNA, so they effectively bought us out."
Close up on polycarbonate roof and panels|
That was about 4 years ago. Since then Soccer City has been constructed, accolades have been won and many hours have been channelled into this structure intended for use as a multipurpose stadium for rugby and other sporting events as part of the City's 2010 Legacy Programme.
The precinct around the stadium has been upgraded to incorporate a transportation hub and pedestrian mall. New roads and walkways have been built and the upgraded Expo Centre will house the International Broadcast Centre.
Since its birth in 1987 as the FNB stadium and its reincarnation as an African symbol of people coming together in the spirit of co-operation, Soccer City stands proudly as a South African example of our capacity to produce the best when it counts and be counted among the best.
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