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Engineering the Serpentine Pavilion

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Jon Astbury talks to AECOM principal engineer Michael Orr about the challenges of erecting one of architecture’s most short-lived but intensely scrutinised structures

The annual Serpentine Pavilion has been a staple in architecture’s summer calendar for over a decade. Popping up at the end of June to great press fanfare before serving as an events venue until October, this architectural experiment by a newcomer to the UK, while now in the company of many other pavilion programmes, maintains its pedigree, and not only for attracting some of the profession’s biggest names. 

Used as we now are to their rapid appearance, the background work that goes into these architectural one-liners is to a degree taken for granted. Built in just seven weeks, a whirlwind process of architectural resolution, material procurement and construction goes into the Serpentine Pavilion, all based on a design that months before may have been little more than a sketch.

Smiljan Radić was the most extreme. There was little more than a sketch of the egg shape

I meet AECOM’s principal engineer, Michael Orr, at the firm’s London office in Aldgate Tower in a small VR/AR booth, whose interior can be transformed into this or previous years’ Serpentine Pavilions, complete with the surrounding galleries and trees. Since taking over from Arup, Aecom has worked as the project’s structural engineer in collaboration with David Glover, AECOM’s former global chief executive and now chief executive of Intelligent Engineering. Their first pavilion was Sou Fujimoto’s in 2013. It may seem something of an odd fit for AECOM, more commonly associated with vast infrastructure and masterplanning projects, but there is a palpable sense that the Serpentine Pavilion project is a badge of honour, and one that offers the corporate a refreshing shift in scale and working methods. The Serpentine Pavilion is, after all, about the details, be they of the construction variety or the administrative. 

There are some curious samples lying around: a broken section of Fujimoto’s giant climbing frame that failed its stress-test; a charred box from BIG’s ‘unzipped wall’, scorched from tests to ensure it wouldn’t catch fire; and some concrete tile samples for this year’s pavilion. 

‘We do anything and everything that is required,’ says Orr, who has worked on the project since 2016. This ranges from the straightforward issues of DDA compliance and fire regulation that those who haven’t worked in the UK will not be aware of, to devising the entire structural resolution for more conceptual designs. 

‘I think Smiljan Radić was the most extreme example,’ says Orr. He explains that there was little more than a sketch of the egg shape for the engineers to transform into a working structure for Radić’s 2014 pavilion. ‘The people who worked on that had a lot of fun working out what was wanted.’ At the other end of the spectrum was BIG, which sourced all of its pavilion’s constituent fibreglass boxes from Fiberline Denmark, with whom the firm had an existing relationship. ‘They were by far the most thorough, and retained a lot of the design control,’ says Orr, adding that the relationship was more like a traditional one between architect and engineer. It becomes clear that the whole Serpentine Pavilion project exemplifies the relationship between engineer, architect and contractor in microcosm, and is rewarding in the way it challenges how these relationships work.

Serpentine 2018 fea 2675

Serpentine 2018 fea 2675

Orr is tactful about how he negotiates his collaboration with international ‘star’ architects. ‘It depends on their character, and that’s part of the fascination. It’s always the same outcome – but the characters are completely different.’ 

That the Serpentine Pavilion architects have so far not built in the UK, of course, has practical implications: pushing a design back-and-forth to, say, Francis Kéré in Berlin is relatively easier than working with Tokyo-based Sou Fujimoto. This year, the design by Mexico-based Frida Escobedo (five hours behind London, ‘we try not to get too far ahead of her,’ says Orr) may not be pushing any structural or formal boundaries, but it has required its fair share of problem-solving.

The pavilion is a simple, four-walled enclosure, cut through with three internal walls that support a curved, trapezoidal roof. The walls are constructed using concrete roof tiles, in a take on the perforated celosía (lattice) method of wall construction popular in Mexico. Some 10,000 tiles are used to form the pavilion, which is aligned with the gallery’s walls, and along a north-south axis, which conceptually turns it into something of a giant sundial. A sliver of enclosed space not covered by the roof forms a 5mm-deep mirror pool, which can be drained to maximise the pavilion’s usable area for events and adds another layer to the plays of light.

For Escobedo, the structure was driven by the roof tiles – they dictated how large the walls were as well as determining the overall aesthetic

The nature of the Serpentine Pavilion project dictates the use of offsite, and often modular construction, and each year the defining element of each design will be its modules or its overall shape – both presenting their own challenges. SelgasCano’s design, using sheets of coloured plastic, was ostensibly fairly simple. More tricky was finding a fire-resistant material that could achieve the desired effect. Kéré’s 2017 pavilion initially revolved around brick modules; but these had to be swapped for the distinctive blue-painted timber in order to actually stand up.

‘Getting that colour involved a crisis meeting with everyone looking at hundreds of samples of blue,’ recalls Orr. So, things may not always go entirely as planned, but each designer comes with an essential form or module, be it an egg shape or a specific colour or material finish, that the engineers then strive to keep as close to what is imagined as possible. For Escobedo, it is the roof tiles and, as Orr says, ‘the structure was driven by the tiles themselves’. That is to say they would dictate structurally how large the walls were, as well as determining the overall aesthetic.

Realistically, each tile needed to be the same to meet both the budget and timescale of the project. A bespoke production run was necessary to create holes in the tiles prior to their firing in order to avoid cracking when they were fixed. And the tile order needed to be placed well in advance to have them ready in time.

Escobedo has experimented before with takes on the celosía using a variety of arrangements, but here a simple stretcher-bond pattern was decided upon, which could be achieved using one type of tile drilled with four holes (feedback from manufacturers indicated this was the maximum achievable, with one in each corner). The tiles are then slotted, Connect Four-like, onto a series of steel bars to hold the walls in place. 

Aj as floor plan

Aj as floor plan

By February, the design was largely resolved, with Condron Concrete of Tullamore, Ireland, on board to create the custom tiles. With these modules created, the rest is relatively straightforward. Unusually, given the emphasis on offsite construction, this year the superstructure will be welded on site. Orr explains: ‘As everything is quite slender, if you had bolted connections it would’ve just all become about the connections.’ He adds: ‘We’ve got seven weeks, but two weeks is garden works and pouring the foundations, so that’s really only five weeks to get the superstructure in place.’ Each wall module meets at the top with a thin steel section, and along the uppermost edge is a steel cover plate, concealing LED lighting that will illuminate the wall at night.

Given the short timescale, contractors are involved practically throughout the entire process, and Orr speaks of all the ‘little tips’ picked up through this process. When sitting wall modules on top of each other, for example, the contractor added locating pins to ensure each was located correctly with a few millimetres of tolerance. The highest degree of accuracy will be required for the pool space, drained via a series of ACO Drain strips that sit flush with a level of screed 5mm below the rest of the pavilion. Any slight problems here and tiny islands could form. The roof is a simple steel frame, topped with steel plates to form a butterfly roof for drainage and finished on the underside with polished stainless steel to generate the desired reflections. 

And of course, what all of this modular construction also allows for is for the very smooth deconstruction of the pavilion. Come October, the superstructure’s welds can be ground away, the modules separated and tiles removed, ready to go to wherever the pavilion moves next.

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