This year’s design for the Serpentine Pavilion has been described as a psychedelic chrysalis. Tom Webster, the structural engineer responsible for the design, has spoken to NCE about the challenges of such an iconic and bespoke project.
The commission to design the Serpentine Pavilion which sits in the front garden of the small but highly influential Serpentine Gallery in Hyde Park is a sought-after prize for any self-respecting designer. This year Aecom took on the challenge to design this highly bespoke and unusual pavilion, all in a matter of months from start to finish.
The 180m2 pavilion which is roughly a cruciform shape on plan was the idea of Spanish architect Selgascano which wanted to create a layered structure with an inner and outer shell of stained glass effect with light and transparency. It also includes secret corridors between curved and jagged structures wihich form entrances and exits. Structurally 12mm to 15mm diameter steel tubes form smooth arches and faceted portal frames between which coloured ETFE panels span to enclose the space.
The ETFE panels were not the designers’ first choice, however. PVC was initially considered and was thought preferable due to its better elasticity and capability to withstand cycles of being stressed and de-stressed – a key challenge in the demountable design. But as it was not transparent, it was ruled out. ETFE was the next choice but presented some key challenges.
“ETFE is actually quite brittle and so it has a relatively low capacity for strength before it reaches its plastic limit and it becomes like an old pair of tights – it doesn’t hold its shape well and it wrinkles,” explains Aecom associate director Tom Webster.
This problem was overcome by de-stressing the panels as much as possible, some are form found and some are draped allowing them to move up to 50mm in places.
There was also the problem of colour. Non-standard rolls of colour would have had to have been bought in bulk far beyond the needs of the project. The breakthrough for the team came when it discovered that it could digitally print the colour onto the surface of the material. Printing was carried out using a technique akin to the old dot matrix printers, building the colour up with patterns of differently spaced and sized dots.
“This was the turning point. If a panel was vandalised or broken we could simply print another that colour,” says Webster.
Rails on the tops of the steel frames support the edges of the panels and are shaped like a shotgun barrels, with the material fed down the groove between them. This enabled the colour of the structure to change between the frames.
The brief for the pavilion is always to have as minimal impact on the site as possible. Any foundations have to be removed, excavations backfilled and the grass regrown. The impact of water run-off from the structure has to be minimised with no additional loads put on the existing fragile drainage system.
As such the whole structure is supported by a 125mm thick, lightly reinforced concrete slab which varies in level by around 500mm from the entrance to the centre. An attenuation tank under the slab allows any excess water to be held and dissipated over a more controlled time period.