Glulam timber, glass and steel – paired into an elegant and transparent double curved canopy, covering a lush green sunken garden. Concave meets convex: enter The Campus Canopy. This one-of-a-kind structure, designed by Benjamin Thomas of MOLA Architecture, arises on the premises of The Campus, Cherrywood, Dublin. A seemingly simple design: three V-shaped columns carry a curved timber grid covered with glass. But there is more than meets the eye: if it wasn’t for a significant dose of creativity, partnership and technical ingenuity – this canopy wouldn’t be standing here.
After the preliminary design phase of the architect, Octatube was invited to do the pre-engineering. This is our first gridshell project involving structural timber. A range of design workshops organized with the client all evolved around the central question: how can we get this built – keeping it technically feasible and yet remaining close to the design intent?
Our team of structural engineers took up the task of optimizing the complex geometry, and thus defining the shape of the timber gridshell. Criteria were identified that assessed each option (e.g. weather exposure, connections and production). The results were recorded in a matrix, in order to choose the best option. Timber is a beautiful material to work with, but it raises material-specific challenges - especially when using it structurally.
The edge beam: a game of hiding connections
The timber typology of the Campus Canopy consists of three beams: the edge beam, the primary beam and the secondary beam. The slim edge beam goes all around the canopy and consists of a single curved beam, except at the corners, where the beam is double curved. It slightly changes shape throughout and has different inclinations (for maintenance). This beam was particularly challenging from a structural point of view, as timber doesn’t resist torsion very well. Forces had therefore to be transferred between the edge beam elements by a large steel connections.
Even looking from up close, there are no steel connections visible between the different edge beams – you’ll only see timber. We managed to hide the connections using a steel insert, emphasizing the fluidity of the design. The same was achieved in the primary beams (the beams that go from front to back). All primary beams are different and they change in shape and curvature/radius. However, the connections to the edge beam are fluent.
Cold bending on a natural material
A lot of testing was done in the mock-up phase. It was particularly informative for the torqued panels that would be cold bent on site. Quite the challenge given the double curvature of the structure. Single curved panels are relatively easy to work with, but panels that are curved on four edges are extra challenging. Additional iterative calculations were therefore necessary to keep resulting local tensions under control.
As the canopy needs to be walkable for maintenance, the combination of cold bending and the point load was critical. Ideally, thin glass is used for cold bending, whereas thicker glass is desirable for the point load. It was a search for the right balance.
Bespoke solutions for maintenance
How to maintain a canopy with such strong inclination? Bespoke solutions were necessary to tackle this challenge. We incorporated fall arrest brackets in the canopy, they were attached with long screws. A challenge in itself because, how to insert straight screws in a curved beam? A solution was found in brackets with a recess in the beams. Besides fall arrest we incorporated rope access as well, from which the maintenance should be done by trained personnel.
Rigid columns vs. breathing canopy
When the temperature changes, and the wood expands, the glass can move slightly on its profiles – the roof can breathe. This is also accommodated in the columns, fabricated, transported and installed as single V-shaped pieces. It comes down to the details and although these robust columns might suggest otherwise, it truly is precision work. The way it is fixed in the foundation, the distance between the foundation and the roof, the distance between the elements of the column: it is a meticulous interplay. If they don’t come together perfectly, the construction wouldn’t function. Given the big welding assemblies of these columns, and the fact that welding causes heat (and thus deformations), it is a true feat how everything came together in the end.
Partners in this project: MOLA Architecture, Cleary Doyle Construction Lt, Scollard Doyle Construction Consultants & Billings Design Associates