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Serpentine Gallery Cracking a design maze

Challenge and compromise have characterised the design and construction of this year’s Serpentine Gallery Pavilion in London’s Hyde Park. Max Thompson reports.

Architect Sou Fujimoto’s design for this year’s Serpentine Gallery Pavilion in London’s Hyde Park comprises a mesh of 400mm square steel frames arranged to create a cloud-like structure. The structure takes the form of an irregular, semi transparent ring, apparently floating above the ground, and accommodates a café and venue space.

The building is relatively small, occupying a footprint of 350m2, but tight timescales and engineering and fabrication issues have created challenges for the project team, which is now seeing the project come to fruition.

One of the earliest designs for the cloud mesh consisted of a “modular mesh” of cubic steel frames with 400mm long sides.

But in Aecom’s London office - some 14,000km away from Fujimoto’s Tokyo studio - project engineer Tom Webster foresaw problems. He calculated that limiting the size of the frame sides to 400mm meant that the structure would require around 37,000 lengths of steel tubing and up to 7,000 joining ‘nodes’.

Time was tight. “We had six weeks to design, six weeks to fabricate and six weeks to install,” says Webster. “To fabricate that amount of steel in that amount time wasn’t going to be possible so we looked at some way of creating the same form with fewer steel members,” he explains.

The solution suggested by the Aecom team was to swap a proportion of the 400mm sided frames for others with 800mm sides and in doing so considerably reduce the amount of steel needed.

As well, it became apparent that 800mm sided shapes had the advantage of being easier for workmen to access. The steel is being fabricated by Yorkshire based Stage One.

Fujimoto also originally wanted the shapes to be formed by 15mm sided solid steel square tubes, but again, lead-in times said otherwise. Webster and his boss, chief executive of Aecom’s building engineering division, David Glover, tabled a compromise using an off-the-shelf 20mm square profile.

Getting buy-in from the architect was never going to be easy.

“Being remote from the client and the engineering team, I think they felt defensive at first,”says Webster.

“They were developing their concept, then we came aboard and said ‘Hang on chaps, you have to think about welding time and procurement time.’

“David flew over to talk to Sou Fujimoto and took a whole load of our development work with him…to let them touch it, feel it; to make them feel involved in that process.

“As soon as they understood that they came on board and the rest of the design followed very quickly.”

Those very early days, concedes Webster, had their moments: “In any project there is a bedding-in period when you get to know people and how they work; but on this we had to do this bedding-in period in a matter of hours.”

The decisions to use larger 800mm sided shapes cut the amount of steel needed down to 27,000 individual lengths and 3,500 ‘nodes’.

Those nodes are welded half joints with an additional 15mm diameter rod running through the core of the steel, the ends of which slot into adjoining tubes (see diagram).

Another factor was deciding how much of the 18m x 18m structure could be built within the 25m x 25m area set aside for construction, and how much could be prefabricated.

Stage One settled on 56 prefabricated modules and used state of the art laser cutters and a host of skilled welders to create them. The modules varied in size, but the largest was 18m x 2.4m x 3m, matching the dimensions of the biggest available flatbed truck that would be needed to transport them from York to London.

Like its 12 predecessors the 2013 pavilion had to be demountable so the connections between the modules was an issue: “We didn’t really want a series of welded up nodes that you would have to break or cut to dismantle the system,” explains Webster.

So, they developed a joint. Where the largest modules are connected to each other an 8mm hole was drilled and tapped allowing the two units to be bolted together.

nodes

Webster, who includes the Spartak Moscow Stadium and Rio de Janeiro’s 2016 Olympic structures in his portfolio, describes the gallery as the most complex building he has ever worked on. “It’s got more structural members than the Eiffel Tower,” he says. Incredibly, though, there has only ever been one engineering drawing.

“We have done one drawing to date so they could set out the ground floor,” he says. “Everything else, the engineering and the architecture, is all in a building information modelling (BIM) environment,” Webster says.

For Glover, being immersed in the BIM environment has been the most intriguing feature of the project: “Ten years ago, maybe even five, we would have struggled. But from day one we were working in a big 3D model, analysing it, rendering it and sending it straight to production at Stage One.”

The process started with the original geometry coming in from the architect in Rhino3D-modelling software. Aecom then exported it to its own ‘parametric script’.

“The parametric scripts lets us do whatever we want,” says Webster. “In this case it was programmed to reduce the density of the cubes.”

The remodelled design was exported into Excel and fed into Aecom’s analysis software to check how it behaved under various forces and stresses. Once passed, it was put back into the Rhino software and sent to Fujimoto for final sign off.

But while state-of-the-art parametric computer design was fundamental to the scheme’s success, the Aecom team was fascinated to see how Sou Fujimoto relied on good old-fashioned, hand-made, scale models to test certain concepts.

“They work very much in the physical model world,” says Webster. “Their office (in Japan) is more like a craft workshop, whereas ours looks like a computer lab,” he adds.

“We sat there for two days making models,” says Glover. “They made a model of the 15mm tubing out of balsa wood to understand if it was going to be critical; the model helped them realise that at a bigger scale, it was not.”

Despite its architectural licence the pavilion is ultimately a venue and as such it has to comply with building regulations. Fire escape signs were one potential headache; Webster describes them as “inartistic and unwanted”’. In the end as the building is open on two ends with obvious means of escape, minimal signage was permitted.

Another issue was how to offer the 750,000 or so visitors expected to visit the pavilion some protection from the elements.

Doing so without compromising its transparent, cloud-like mesh proved troublesome.”It took a lot of design development. The original design was a polycarbonate disc sat in the middle of each cube,” says Webster.

polycarbonate discs

Because this required “nasty ,connections” to the uprights the design evolved to consist of overlapping polycarbonate discs; each cut just over half way and clamped in position.

Glover has worked on six Serpentine galleries beginning with Frank Gehry’s timber pavilion in 2006. The previous five were with his former company Arup including last year’s pavilion, designed by artist Ai Weiwei and Herzog & de Meuron. But when he jumped ship his high-profile client went with him.

For Webster the Serpentine appointment is a game-changer as far as his company goes: “We have a bad press, people think we are just a bunch of project managers. We are not.”

Glover agrees: “Aecom is viewed by some as a big multinational, ‘acquiring’ company, and people want to know if it has a design culture.

“For me,” says Glover, “the Serpentine Gallery shows there is ‘design’ in the company.”

The thirteenth Serpentine Gallery pavilion opens on 8 June. Go and judge for yourselves.

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