The annual Serpentine Pavilion in Hyde Park in London opens to the public this week. This year it is joined by four bespoke summer houses. The engineers behind the structures have spoken to New Civil Engineer about the engineering challenges.
The main pavilion is designed by architect Bjarke Ingels Group (BIG) and engineering consultants AKT II. It signifies an “unzipped wall” and is one of the tallest pavilions built on the site to date.
This year an additional four summer houses have also been built around the 18th century Queen Caroline’s Temple, a short walk away from the main pavilion itself. The four very different structures have each been designed by different architects – Kunlé Adeyemi, Barco Leibinger, Yona Friedman and Asif Khan – with consultant Aecom carrying out the structural engineering.
Each of the houses is constructed from different materials and has its own unique engineering challenges. However, they were all united by the restrictions put in place by the Royal Parks to have as light a touch as possible, meaning no cranes or deep foundations were allowed to be used and their weight had to be minimised. Each of the houses is built on a steel plate foundation which was brought to site in sections and welded together.
Work on the summer houses started in January of this year and construction of the four structures was limited to just three weeks. This led to the focus being on off-site construction.
The first Serpentine Pavilion was built in 2000 by the late Zaha Hadid. Previous collaborations have included Frank Gehry together with consultant Arup in 2008, and Selgas Cano last year in collaboration with Aecom.
The main pavilion
The main pavilion is 14m tall, 27m long, 13m wide and forms two highly curved walls which meet at the top, creating an arch which effectively spans 14m.
“The form, if you look on plan, is two sinusoids offset by half a wave,” said AKT II design engineer James Kingman. “The north wall is completely symmetrical, then by lofting those two curves to a common straight line at the top, that’s what creates this freeform surface.”
The ”blocks” in the wall are formed from Fiberline “Lay Light” panels – translucent glass fibre reinforced polymer (GFRP) sheets which have been bonded together to form 400mm by 500mm rectangular tubes.
The curved geometry of the structure was formed by offsetting the tubes from its neighbour, although the different lengths of the boxes was rationalised to a 50mm grid to simplify the construction. There are still, however, around 700 variations of blocks with varying lengths up to 2m long and wall thicknesses of either 3mm, 6mm or 10mm depending on the load it is carrying and the amount of light required to penetrate through it. There are 1,802 blocks in total.
The design of the pavilion was taken from a model in the specialist 3D software Rhino. The structure was then built up from a 2D frame analysis to multiple 3D models.
“We then went into a full blown 3D sophistic model,” said AKT II director Ricardo Baptista. “It was a super heavy model which took a number of hours to run, especially when you add a buckling analysis, non-linear analysis, second order effects. We didn’t go into a non-linear analysis straight away, we built it up as things got more fixed.”
The computer model was then physically tested by fabricator Fiberline at its facility in Denmark.
From the beginning of the project Baptista said the focus was on the detailing of the finishes. The 1.4km of extruded aluminium angles which connect the blocks together have been designed to be 35mm short of each end of the tubes to create a shadow gap and the 30,000 bolts, which connect the boxes together, were bespoke and countersunk to minimise their impact on the structure, he said.
The construction time on site was tight, said Kingman, so the emphasis was on offsite manufacture. As a result, the Fiberline tubes were manufactured in Denmark and then shipped to the UK. Here, Yorkshire-based specialist contractor Stage One, assembled the blocks into rows of four by three and drilled the holes for the connections. From there, the blocks were meticulously labelled and construction began on site.
In total the design was carried out in three months with around six weeks construction on site.
Kunle Adeyami’s structure comprises a steel frame with 30mm thick sandstone panels which clad the exterior like a rainscreen cladding. The foundation, like all the other foundations for the summer houses, had to be limited to thin steel baseplates to have ‘as light a touch as possible’, said Aecom director Jon Leach.
“How do we deal with the interfaces and the tolerance between the different materials?” he asked. “We had Grants doing the stone to an incredibly high quality and tolerance compared with the more furnished construction internally.”
One of the challenges with this structure, explained Leach, was sizing all of the different parts of the structure to ensure that they were within manageable limits due to the restriction in lifting equipment allowed on site.
“Tying to limit the size of each piece – that was more difficult with the stone,” said Leach. “We spent a lot of time with the Stage One engineers going through all of the shop models and agreeing with where the splices and connections would be and how that would then impact on tolerances, whether the joints in the steelwork would work with where the joints in the stone work would be. It was very hands on with all of the different materials.”
The curved structure designed by Barkow Leibinger is geometrically complex with a thin steel frame which has a bonded and nailed 4mm to 6mm stressed timber skin on the exterior to develop the composite action. The structure is around 8m by 5.7m on plan and 3.9m high.
“It was a very repeatable structure, but geometry was the thing that governed the design on that. We spent a lot of time exchanging digital models with the architect to make sure they were happy with the shape,” said Leach.
He explained that because of the complexities involved in the design, the team conducted a number of scale tests on models and then used an augmented reality headset to check the structure.
“The geometry is so difficult to generate and to check, so we used some augmented reality headsets to project the image into a room and we could walk around a 3D model,” added Leach. “Look at ways of using the new technologies and there’s a certain novelty value around then, but it was genuinely useful to do the design review with that one.”
Leach said this summer house was one of the more interesting houses to design. He said the team worked from images of models which architect Yona Friedman had built from paper and had marked up with pen. This allowed the team to have some creative input into the design to produce the finished effect.
The house comprises modules of 16mm diameter wire cubes, built up to 11.5m high. It is the tallest of the summer houses and to minimise working at height, construction of the cubes took place at ground level and were lifted up, another slotted in underneath and the structure welded together. An engineering model was produced, but in reality, explained Leach, it was all about structural principles and understanding the way the materials responded.
This design was inspired by the fact that Queen Caroline’s Temple was positioned in a way that it would allow it to catch the sunlight from the Serpentine lake, said architect Asif Khan.
Leach said that this was “beautifully simple as a concept” and because of this it was all about the seamless detailing of the wooden staves, but could be quick to build and would be demountable at the end.
The 4.5m high timber staves, he said, were able to be erected into curved housings at the base in a very short space of time, but the time consuming part was in the detail.
“The staves could be installed in a minute, but the time came in the fine tuning of it and lining up the top,” said Leach.