2015 BOUWEN MET STAAL

Transcription

1 Interview Mike King, Principal Arup, Singapore Bigger spans by small steps As a keynote speaker at the IASScongress (International Association for Shell and Spatial Structures) in Amsterdam, August 17 th till 20 th, structural engineer Mike King (1968) talked his audience through the engineering of the Singapore National Stadium, the world s largest free spanning dome structure. Behind the scenes King, currently Principal at Arup s Singapore office, looked back on his earlier work and discussed the influence latest digital technologies have on today s method of design, engineering and steel manufacturing. Over his 21 years with Arup, King has specialized in long-span structures for major stadiums, airports, sports arenas and train stations. King worked in New York, London, Singapore and his native country Australia after graduating as a civil engineer at the University of Wollongong. His work includes one of the three bidding teams for the Olympic Stadium in Sydney, which tender wasn t selected, the Bangkok Asian Games Stadium and the Toronto Airport, the latter being a design driven more by reducing commercial and program risk than creating an engineering marvel. King: The structure itself isn t that adventurous or complex, yet beautiful in its simplicity as well. Manchester Stadium Kings involvement with the Manchester Stadium for the 2002 Commonwealth games (athletics) stands out due to its early example of adaptability. Also known as the Etihad Stadium it was built in 1999 and subsequently converted into the City of Manchester Stadium for the sole purpose of soccer. A rectangular football pitch, an ellipse running track and all visitor areas were initially planned, so the stadium could permanently change into a football stadium. Three sides were made in 1999 and after the games the fourth side was built and an extra lower seating tier was actually dug in the ground, so the 41,000 seats 4 Oktober 2015 BOUWEN MET STAAL 247

2 Foto: Darren Soh athletics arena was upgraded to 48,000 seats situated close to the pitch. In 2015 a third ring was added. Beijing Airport Beijing s Airport Terminal 3 by Foster + Partners is more distinctive for its building speed than its structure, says King. The Chinese government simply decided that the project had to be completed in Omitting any delays on building permits and working along 24/7 working shifts the gigantic building was actually finished earlier than calculated for start of the 2008 Olympic Games. Built to facilitate a capacity of 50 million passengers a year (by 2020) the roof is 3 km long and 1 km wide. The roof structure of 360,000 sq. m is a Mero -type steel space structure with cantilevers and cantilevering steel columns. All without bracing and movement joints. King s Cross Entrance Building Renowned for its modern intervention King s personal favourite however is the diagrid-shell roofed new entrance building for London s King s Cross Station set against the historical 1852 train station building. Designed in the project plan s were put aside as too costly a project until the 2012 Olympics came through while meanwhile a poor temporarily construction from the 1970 s remained. By 2012 the project finally was finished within the same scheme, as part of the overall restoration of King s Cross. From scratch the project was a necessary joint collaboration between the architect (John McAslan and Partners) and Arup s engineers. King: John and I designed it together to the most efficient form. I can see my own signature. It would have been different without me, of which I m mostly proud of. With its single-span structure measuring 54 m from centre to circumference, and covering an area of basically three Olympic swimming pools, one of its achievements was overcoming a strictly limited number of foundation locations and avoiding loading the adjacent historic rail hall building. The kind of reverse waterfall of white painted steel has 16 perimeter columns and is clad with 1,200 solid and 1,012 glass triangular panels. London Aquatics Centre Again for the London 2012 Olympics King s work on Zaha Hadid s London Aquatics Centre was altogether different. King: The form which symbolises water in movement through symmetric arches, was already defined. The structure was subordinate and we filled in the blanks. The 160 m long and approximately 80 m wide BOUWEN MET STAAL 247 oktober

3 King s Cross Entrance Building. Foto: Darren Soh Interior of Beijing s Airport Terminal 3. Manchester Stadium (Etihad Stadium). Foto: David Millington photography Foto: Darren Soh roof, weighing at 3,000 t, was constructed using aluminium roof cladding, 3,000 t of structural steel, and 70,000 bolts. King memorizes: It was built during the global economic crisis and contractors weren t very keen due to its immovable deadline, complexity and financial and program risks. At first there was concern that no one would tender for the project, but through a competitive dialogue process, at which point the steel structure was discussed, the final contractor was found. The steel nodes were complex because of the many joints which come together but the roof trusses aren t, because they re mainly designed as 2D straight elements. The purlin system is the only element of bent steel structure and are single bent in one plane from standard beam sections for economy. Singapore Sports Hub The 55,000 seats National Stadium of Singapore (photo p. 4 and 5) is the centrepiece of the Singapore Sports Hub project completed in The roof is a dome structure spanning 310 m with a rise of 85 m from ground level. The roof structure is the largest dome roof in the world covering a stadium and supports a symmetrical movable roof in two halves. The structure is formed by a series of arches shaped triangular steel trusses varying in depth from 5 m at the centre to 2.5 m at the base and a post-tensioned concrete ring beam support. These trussed arches are constructed from S355 steel elements and span in multiple directions and cross the roof opening to form a braced dome structure. Due to the movable roof there is a varying load on the structure and fatigue has been considered. King: To manage the design of the huge multi-element structure parametric design software was used as well as software specifically developed for the project to optimise and exchange information between architect and engineer, and then to fabrication. King agrees that todays methods of design and engineering do have an impact on buildability. The new possibilities of the latest digital technologies influence performances and design but are accelerating at that. Where does this leave the steel fabricator? A lot is still fabricated by hand with manual welding and sometimes with quite old, robust but reliable equipment. Surely it goes with the territory of the work- 6 Oktober 2015 BOUWEN MET STAAL 247

4 London Aquatics Centre, including two tribunes during the 2012 Olympic and Paralymic Games. Foto: Darren Soh shop as well: Within the Manchester project there were these masts of forty meters long with a huge arrow on top which gathered all the cables. When visiting the steel manufacturer I noticed at the end of a lane a humongous kind of spear, completely hand welded, lying with the peak in the ground. I thought it was the foundation of an oil platform. And the steel fabricator said: But that s your mast. That s the gap. We re making a virtual reality. Engineering happens at a desk through a small screen, with a model, that s easily manipulated with clipping, enlarging and turning around. The steel thicknesses are defined by the forces, it doesn t matter how big or small, the software generates and regenerates. But in fact we re acting with real, big elements. Connections can sometimes be bigger than a room. How do you cross that gap? By taking small steps. One of the issues indeed is the scale and complexity. We have automatic welding machines on long straight runs, but still there s manual work. For the Singapore National stadium we had 20x50 mm thick hollow sections welded onto base plates at the supports. The tubes can be cut by cnc-processing. But the industry does not have yet the robotics that can weld them together in this configuration. Steel manufacturers will need to make a step change. The obstacle we have to overcome is the certainty in quality, of the thickness of the welding, whether there are cracks or not. I guess when that level is reached within software and robots, we have the leap we need. Neighbouring disciplines Also the building industry can pick up ideas from neighbouring disciplines experiments. King refers to a shell structure (15x6x4 m) in plywood developed at the Singapore University for Technology and Design. Without drawings it was assembled from machine numbered plywood plates which were cnccut at the factory. A script was taken from the Rhino model providing the best cut out of standard sheets for minimum waste. Completely random cut but digitally numbered with all the holes in the right places in the wood and for the steel connections. The work was carried out by a furniture manufacturer, outside of the building field, while it was assembled largely by students. A fantastic example of what s possible. In general: We have to tool up to larger scales. Automation is necessary but requires investments from the steel industry. They have to be prepared. As an example: We ve designed a beautiful modern shaped sculpture in London looking high tech, especially in stainless steel. It was high tech in analysis and in engineering, but the tubes were made using old lathes from WW II. It s not unusual for the industry, this mix of high-tech design and low-tech construction. Is it still possible to calculate these complex structures by heart? Just roughly. With the new possibilities in complex free forms you can t optimise without software. In Singapore we calculated the connection designs with finite element models, not only on elastic behaviour but also second order effects and plastic behaviour. BOUWEN MET STAAL 247 oktober

5 London Aquatics Centre in its final stage, after removing the tribunes. Foto: Stratford Legacy An independent checker, comparable to the Prüf-engineer, had to deal with approximately 2,5 million pieces of information: 25,000 members, at each end two on each with axial forces and lateral shear forces, torsion et cetera, so six cases. Impossible without a computer. Does your work become easier with these modern means? That concerns me. When you ask a young architect or a graduate to draw his idea, he or she mostly grabs a laptop and not a pencil. It looks great, but is it still buildable? I think the seniors must assist the young grads. Ultimately, we re building things. You have to go on site and see. I m still learning everyday. But, to answer the question: it has not become easier. The pressure has gone up. You have more complex projects with extensive engineering and a client asks for more alternatives in shorter time frames. Parametric design is inevitable with these fast paced requirements. Exchange and consult Crucial in working with parametric design is exchange, to make sure all is well in time and under budget at the delivery end. Therefore communication, as an information carrier to and from architects, engineers, contractors and steel manufactures must also be digitalised and the production must be automated in the same language. King: In doing so we expect all parties to benefit. If you don t get on board with the right tools and equipment, you re out. Obstacles are the amount of software packages, mostly incompatible. Which to choose? I also think designers, engineers and manufacturers must consult each other. When a connection is designed with welds and the steel contractor switches to bolds, according to company tradition, there can be a problem in terms of structural weight and structural behaviour. This goes for constructing the Singapore Stadium as well. The erection of the roof had a special temporary working method, from one side to the other with the roof supported on specific temporary towers. At every stage of its erection the structure had to be verified to determine the locked-in stresses. One tendering steel contractor offered a variant erection from one end and progressively de-propping the erected western portion of the roof as he was still completing the eastern portion, claiming to build faster and therefore cheaper. But then the original structure would have had to be recalculated and redesigned because of extra bending and stresses resulting in more steel say 140 kg per sq. metre instead of 110 kg s and more laborious connections. Finally we could convince the client not to change. Proofing that communication still is crucial. On the other hand: during the same engineering period we had some technical questions. The steel contractor to whom the project was awarded, Yongnam, was very eager to build the stadium from a very early stage prior to being awarded the contract. When asked for their advice they showed up with eight to ten senior persons with whom we optimised the scheme and structure. So you see, a large part relies on human contacts, skills and people s work. 8 Oktober 2015 BOUWEN MET STAAL 247